Effects of land use change on soil physicochemical properties in selected areas in the North West region of Cameroon

Effects of land use change on soil physicochemical properties in selected areas in the North West... Background: Land use changes from natural ecosystems into managed ecosystems may have deleterious effects on soil structure and quality. This study characterise the soils under, and assesses the effects of different land use systems on selected soil physicochemical properties in the North West region of Cameroon. Six land use systems including: natural forest, natural savanna, grazing land, afforested land, farmland and Eucalyptus plantation were identified. Ninety soil samples were collected from each at the 0–15 cm depth. Fifteen soil physicochemical properties were measured. Results: The conversion of natural forest or savanna to farmland reduces the silt contents, moisture content, organic matter, organic carbon, total nitrogen, available phosphorus, pH, cation exchange capacity and exchangeable bases, but increases bulk density, electrical conductivity, exchangeable acidity and sand content significantly (P < 0.05). The results revealed that deforestation and subsequent cultivation of soil had negative effects on the measured soil properties. Conclusions: Land use change has ruined soil quality in the North West region. To reverse soil degradation and promote restoration, emphases should be placed on promoting the use of sustainable land management practices within the savanna, grazing, agricultural and forest management systems. Keywords: Soil quality indicators, Land use change, Soil degradation, Africa, Cameroon changes are indicators of forest resource dynamics within Background a landscape. The dynamics of LULC change associated Land use/land cover (LULC) changes influence the bio - with the anthropogenic activities are occurring rapidly geochemistry, hydrology, and climate of the earth. Eluci- in tropical landscapes. Recent international concerns dating the impact of LULC at the local to regional scales place high attention on monitoring changes in tropical on soil quality status is not direct but rather complex to resources and reporting on those factors (such as agricul- guarantee any generalizations (Hoogsteen et  al. 2015). ture) influencing these changes (such as deforestation), Across sub-Saharan Africa, natural resources remain for consideration of novel scientific and policy inter - central to rural people’s livelihoods (Roe et  al. 2009). ventions (goal #15 of the 2030 Agenda for Sustainable Nonetheless, natural (rainfall and temperature) as well Development). To understand the dynamics of ecologi- as anthropogenic (farming, grazing, burning) forces can cal processes and the impacts related to these changes in exert pressure on these resources, thereby influencing LULC, an assessment of the effects of these changes on spatial and temporal scale changes on a landscape. LULC soil quality is important. According to the United Nations Convention to Com- *Correspondence: tvasong@yahoo.com bat Desertification (UNCCD), 24 billion tons of fertile Department of Development Studies, Environment and Agricultural soils are lost due to erosion every year, while 12 mil- Development Program, Pan African Institute for Development-West Africa lion hectares of land are degraded through drought and (PAID-WA), P.O. Box 133, Buea, South West Region, Cameroon Full list of author information is available at the end of the article © The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Tellen and Yerima Environ Syst Res (2018) 7:3 Page 2 of 29 the encroachment of the desert (this is 23 hectares per sea level. Three study sites were selected following a minute) where 20 million tons of grain could have been stratified random sampling technique. Each stratum rep - grown. Epule et al. (2011) stated that Cameroon’s forests resents a particular topographic zone [the lower altitude are part of the Congo Basin and it is ranked the second (<  900  m); the mid-altitude (900–1500  m) and the high largest tropical rainforest hot spot in the world after the altitude (>  1500  m)] within the North West Region. The Amazon Basin in Latin America largest. FAO (2010a) representative study sites selected include Ndop (lower remarked that Cameroon’s forest contains about 2696 altitude), Nkwen (mid-altitude) and Awing (high altitude) million metric tons of carbon in living biomass. This (Fig. 1). indicates that deforestation is even more intimidating The topography greatly influences the climate with a for the environment. Even so, FAO (2010a, b) reported tropical transition from the rainy humid and continu- that Cameroon forests occupies about 28 million hec- ously warm climate in the South to an extremely unpre- tares (ha) of land and of this number, about 220 thousand dictable (regarding temperature and precipitation) (ha) are lost each year; this is equivalent to about − 1.0% but somewhat dry and hot climate of the North. Abso- of annual forest cover loss. Evidence, though anecdotal, lute annual average precipitation ranges from 1700 to reveals that the population growth in Cameroon and 2824  mm. The high altitudinal areas are cold (<  15  °C) scarcity of arable land has exacerbated food insecurity such as Awing and Santa whereas the low altitude zones and water scarcity. FAO (2009) forecasted that the high are hot (average 27 °C) such as Ndop plain and Ako Sub population density with continued demand for arable Division. There are two distinct seasons: the rainy season land in Africa would amplify deforestation pressure. In (mid-March to mid-October) and the dry season (mid- fact, land degradation is a very serious challenge as it October to mid-March). The vegetation here results from leads to hunger, poverty and is at the root of many con- the prevailing soil conditions, altitude, human activities flicts (FAO 2017). Progress towards meeting the sustain - on the environment and climate. The region lies within able development goal # 15 of the 2030 agenda requires the savannah zone where grasses and shrubs predomi- an understanding of the drivers of soil degradation. nates. The dominant soil type is Oxisol (rich in oxides of It is reported that an ample surface area of African Fe and Al and has a characteristic reddish color) which forests has been lost, with a significant influence result - encourages erosion (pseudo sand and pseudo silt) and ing from small scale agriculture (FAO 2009; Harvey results to gullies on bare surfaces while the valleys are et al. 2004). In fact, Cheek et al. (2000) and Harvey et al. covered with alluvial deposits (Yerima and Van Ranst (2004) projected a 96.5% future loss of the original for- 2005a, b; Yerima 2011). est cover within the Bamenda Highlands, with its climate change implications. The need for sustainable land use- Land use/land cover systems identified in the North West ecosystems conjures the protection and enhancement Region of soil quality through designing efficient site specific Six LULC systems were identified and presented as actions to control erosion and restore soil quality, thereby follows: improving the conditions and productivity of the agro- silvipastoral landscapes in the western highlands region i. Farmland: It is characterized by the cultivation of of Cameroon. The objectives of this study include: (i) to crops such as cabbages, onion, carrot, pumpkins, characterize the soils under the different land use sys - and green pepper. Annual crops such as maize, pota- tems; and (ii) to assess the influence of land use change toes, beans, and pea, are most commonly cultivated on selected soil physicochemical properties in the North (Fig.  2). Subsistence farming characterizes agricul- West region of Cameroon. ture in the study area, and the main cropping system is mixed, although rotation, inter-cropping, mono- Methodology cropping and fallow systems are also common. Description of the study area ii. Natural forest land: It is composed of various indig- This study was conducted in the North West Region enous trees, shrubs, and bushes like Podocarpus of Cameroon which lies between latitudes 5°45″ and falcatus (Zigba) (Fig.  3). The forest is usually found 9°9″  N and longitudes 9°13″ and 11°13″  E. It covers an in protected areas where it is restricted from farm- area of about 17,400  km and is bordered to the North ing or livestock grazing. However, the culture has and West by the Republic of Nigeria, to the South by not allowed replanting (reforestation) and the newly the West and South West Regions and to the East by the germinating seedlings are being destroyed by farm Adamawa Region (Manu et al. 2014). The topography of encroachment and animals browsing and trampling. the Region varies greatly from depressions lower than Due to high deforestation rates, these forests are 400  m above sea level to high mountains, 3000  m above found in patches, often located in valleys and small Tellen and Yerima Environ Syst Res (2018) 7:3 Page 3 of 29 Fig. 1 Topographic map showing the locations where soil samples were collected within the North West Region of Cameroon depressions which often harbor streams and other cies include: pine, Zigba (Podocarpus falcatus), large water bodies. diameter rattans (Laccosperma secundiflorum and iii. Natural savanna: It is composed of short grasses and L. robustum species), mahogany (Swietenia macro- usually located within protected areas (Fig.  4). This phylla King), iroko (Milicia excelsa), Pygeum (Prunus land use system is used for grazing in areas where Africana), mango (Mangifera indica) and other plant no property right exists. It is believed to have been species that have food, fuelwood, medicinal, timber, created due to the shrinkage of the forest cover as a etc., attributes (Yerima 2011). result of deforestation due to human and animal dis- vi. Grazing land: It consists of short grasses (pasture) turbance. and used for cattle grazing and is considered a com- iv. Eucalyptus plantation: It predominantly consists of munal land (Fig.  7). Under such interference, it has two commonly known exotic eucalyptus species in become very difficult to find natural settings in the the region (Eucalyptus salinga and Eucalyptus gran- area (Yerima 2011). dis). These tree stands are indiscriminately planted on water catchments and are gradually replacing Soil sampling and analysis native tree species of the NW region (Fig. 5). The soils were characterized following procedures v. Afforestation area: It is represented by an afforested proposed by (Yerima and Van Ranst 2005a). Soil sam- research unit created in 2010 (6–7  years ago), char- ples were collected from the six main land use systems acterized by fast-growing environmentally friendly described above (Natural forest, natural savanna, farm- tree species for fuel and timber (Fig.  6) to reduce land, afforested land, grazing land and Eucalyptus plan - pressure on the endangered native tree species which tation). Under each land use, soil samples were obtained are at risk of extinction. Some of these plant spe- from a plot, with dimensions of 20 × 20 m (400 m ), at a Tellen and Yerima Environ Syst Res (2018) 7:3 Page 4 of 29 Fig. 2 Collection of soil samples from farmlands on varying geo- Fig. 3 Protected man-made forest at the Yongka Western Highlands morphic surfaces (a); a common tillage practice on farmlands in the Research Garden Park (a); the collection of soil samples from a natu- North West Region (b) rally protected forest adjacent to Lake Awing (b) constant depth of 0–15 cm, following a “Z-layout” design. soils were analysed at the Soil Science Laboratory at the Soil samples were taken from the four corners and center University of Dschang, following standard procedures of each layout. Approximately 1  kg of composite sample and methods as described below: was collected from each location and placed into plastic bags. They were then transported, air-dried at room tem - Physical properties perature, crushed, homogenized, and passed through a Moisture content (MC) was calculated using the gravi- 2  mm sieve before laboratory analysis. A total of 90 soil metric method where soil samples were placed into samples (six land use types x five replicates per sample ceramic crucibles and weighed to get the fresh weight plots x one soil depth class: 0–15  cm  ×  three altitudi- and then oven-dried at 105  °C to constant weight for nal zones) were collected within the study area, from about 24  h and the dry weight recorded. These values June to July 2015, for analysis. Undisturbed soil samples were then used to calculate the moisture contents of the were taken with a core sampler that was 7.5  cm long soils using the formula: and 6.4  cm in diameter for bulk density determination. 100 (fw − dw) Soil quality indicators comprising of the three standard MC (%) = dw groupings including: physical (moisture content, bulk density); chemical (pH, total nitrogen, available phospho- where MC soil moisture content (%), fw fresh weight (g) rus, exchangeable bases, cation exchange capacity, C/N of soil sample, dw dry weight (g) of soil sample. ratio, electrical conductivity) and biological (organic mat- Bulk density was measured following the core method ter content) proposed by Yerima and Van Ranst (2005a), described by Yerima and Van Ranst (2005a, b), where for soils in the tropics, were selected for analysis. The samples contained in the core rings of known weight, Tellen and Yerima Environ Syst Res (2018) 7:3 Page 5 of 29 Soil bulk density was then determined using the follow- ing formula: BD = M/V, where BD bulk density, M mass of oven dry soil (g) and V volume of core (cm ). Soil textural fractions (sand, silt, and clay) were ana- lyzed following the Bouyoucos hydrometer method, where 15  g of 2  mm air-dried soil was weighed into 500  ml beakers and subjected to treatments for remov- ing organic matter using H O , followed by dispers- 2 2 ing the soils with sodium hexametaphosphate (Pauwels et  al. 1992). The resulting compositions were placed on a mechanical shaker and allowed to shake for 3  h. Sus- pensions were then transferred into sedimentation meas- uring cylinders and brought to the 1000  ml mark using distilled deionized water. The mixtures were well stirred using a mechanical rotator to bring the particles into sus- pension. A hydrometer was then used to obtain readings after 40 s (first reading, R1) and 2 h, (second reading, R2) respectively. Calculations were done using the following Fig. 4 Natural savanna grassland located near a palm plantation equations: at Nkwen, Bamenda (a); the collection of soil samples from natural savanna land at the Yongka Park (b) R1 % (Silt + Clay) = × 100 (A) The first reading (R1) gave the silt + Clay content R2 − R1 But % Clay = × 100 (B) Therefore, % Silt  =  A  −  B while % Sand  =  100  −  % (Silt + Clay). After getting the percentage sand, silt and clay, the soil textural triangle was used to classify the soil texture. Chemical analysis Moisture correction factor was calculated using the fol- lowing formula: 100 + MC (%) mcf = where mcf moisture correction factor and MC soil mois- Fig. 5 Eucalyptus salinga plantation at Awing ture content (%). Soil pH was measured both in water and KCl (a 1:2.5 soil: H O/KCl ratio) using a glass electrode Thermo- height and diameter were weighed and the fresh weights Russel pH meter, calibrated using buffer solutions of pH recorded, then oven dried at 105 °C for 24 h, after which 7 and 4 for H O and KCl, respectively. Soil total nitro- the dry weights were also recorded. The volume of the gen (TN) was determined using the Kjeldahl distillation core was determined using the following formula: method (Pauwels et al. 1992) where 1 g each of air-dried soil samples were placed into 500 ml Kjeldahl flasks, fol - 2 3 V = π r h cm , lowed by the addition of 5 ml of distilled deionized water. A scoop of digestion accelerator mixture (sulphuric–sali- where V  =  volume of core (cm ); π  =  3.14; cylic acid mixture) was then added to each flask. Five mil - r = radius = diameter/2 (cm); and h = height (cm). liliter of concentrated H SO was added and the mixture 2 4 Tellen and Yerima Environ Syst Res (2018) 7:3 Page 6 of 29 Fig. 6 Nine year old Eucalyptus saligna tree stand (a); 8 years old Podocarpus (Podocarpus falcatus) tree stand (b); collection of soil samples under a Jackfruit tree stand (c); collection of soil samples under a mixed fruit tree stand (Prunus domestica, Mangifera indica) at the Yongka Highland Research Garden Park (d) was allowed to digest for 1 h in a fume cupboard by gen-0.03 N NH F were used to extract available phosphorus tle heating until the vigorous effervescence subsided to from the soil samples. Phosphorus was determined color- ensure that the digest was free of charred organic matter. imetrically using the ammonium molybdate blue method. The digest was then allowed to cool followed by addition In this process, 2 g of < 2 mm air-dried soil samples were of 20 ml of distilled water. After ensuring settlement, the weighed into clean dried test tubes. Fourteen ml of the supernatant solutions were decanted into 100  ml volu- extracting solution was added and vigorously shaken for metric flasks. The process was repeated and 5 ml of 40% 30  s, using an electrical shaker and immediately filtered NaOH and 100 ml of distilled water were added. The dis - into other previously prepared test tubes carrying funnels tillate was collected and mixed with 5 ml of the boric acid and Whatman # 42 filter papers. For colour development, (H BO ) solution-indicator mixture. The distillate was 5 ml of the extract and standards were pipetted into a set 3 3 titrated with 0.01  M H SO from green to pinkish end- of test tubes. Then, 5 ml of colour development reagents 2 4 point and the titer value recorded. The soil TN was calcu - (Ascorbic acid), and mixed reagent (Ammonium molyb- lated using the formula: date, Potassium Antimony tartrate and sulphuric acid) were added to each test tube. The samples were allowed 2.8 to stand for 15  min for complete color development. Kjeldahl N (%) = (T − B) × M × Absorbance was then measured using a colorimeter, set where T ml of standard acid with sample titration, B ml of at a wavelength of 882 nm. 2+ 2+ + standard acid with blank titration, M molarity of sulphu- Exchangeable bases (Ca, Mg, K , and Na) were ric acid, S weight of soil sample (g), and 2.8 a constant. extracted using 50  ml of ammonium acetate (1.0  M Available phosphorous (Av.P) was determined follow- NH OAc) solution buffered at pH 7. Potassium (K ) and ing Bray-II method where solutions of 0.1  N HCl and sodium (Na ) in the extract were determined using the Tellen and Yerima Environ Syst Res (2018) 7:3 Page 7 of 29 sample was distilled and the distillate in the conical flasks titrated with 0.01 M H SO from a burette. The CEC was 2 4 then calculated using the following formula: EC 100g soil = (V − Vo) × 1.6 where V the volume of sulfuric acid added to the sample, Vo the volume of sulfuric acid added to the blank, and 16 a constant. Electrical conductivity (EC) was determined following standard procedures proposed by Pauwels et  al. (1992) where a 1:5 soil-solution ratio (10  g of  <  2  mm soil and 50  ml distilled ionized water) was agitated for an hour and the readings from an EC meter, calibrated with 0.01 N KCl, recorded. + 3+ Exchangeable acidity (EA) (H  + Al ) was determined for samples with pH < 5.5. In the procedure, 1 N KCl was added to the flasks containing 1  g of  <  2  mm soil sam - 3+ + ple for displacement of the Al  + H ions. EA was then determined by titration of extracts with 0.02  N NaOH for the neutralization of the acidic ions in the extract using three drops of phenolphthalein as an indicator. The exchangeable acidity was then calculated using the fol- lowing formula: −1 EA meq 100g = 40 × t × (Vx − Vo) + 3+ where EA the exchangeable acidity (H   +  Al ) −1 (meq 100 g ), t the exact molarity of NaOH used, Vx the volume of NaOH added to the sample, Vo the volume of Fig. 7 Collection of soil samples from grazing land at Ntambang (a) NaOH added to the blank. and Santa (b) C/N ratio was obtained by taking the ratio of S percent carbon to nitrogen in each sample as follows: SOC (%) 2+ C/N = flame photometer while magnesium (Mg ) and calcium TN (%) 2+ (Ca ) in the extract were determined by complexomet- where C/N the ratio of carbon to nitrogen, SOC the con- ric titration. centration to carbon (%) in the soil sample, TN the con- Cation exchange capacity (CEC) was determined fol- centration of total nitrogen (%) in the soil sample. lowing the extraction method were soil samples were also Soil organic carbon (SOC) was determined following saturated with ammonium acetate buffered at pH 7 to the Walkley and Black wet oxidation method (Walkley displace the exchangeable bases as explained in the case and Black 1934) where 5 g each, of the soil samples, were of the determination of exchangeable bases. However, for first placed into a wide-mouth Erlenmeyer flask, followed CEC determination, the column of each sample was then by the addition of 10  ml of 1  N Potassium dichromate thoroughly washed with 95% alcohol to discard excess (K Cr O ) into each flask, in a fume cupboard. Twenty 2 2 7 ammonium acetate that saturated the complex. This was milliliter of concentrated sulphuric acid (H SO ) was 2 4 verified using Nessler’s reagent. Sixty milliliter of KCl was then added to each flask and the solution mixture was then added to each tube to allow potassium to replace allowed to stand for at least 30  min. One hundred and ammonium ions on the exchange complexes. The fil - + fifty milliliter of distilled water was then added to each trate containing the NH4 ions was collected into 100 ml flask followed by one drop of the indicator Barium diphe - volumetric flasks and brought up to 100 ml mark by the nylamine sulfate. The solution was then titrated with addition of KCl. Twenty-five milliliter of each sample ferrous sulfate solution while stirring the mixture to the were transferred into distiller’s tubes and NaOH added end-point (when the brown colour changes sharply to followed by 2–3 drops of the end-point indicator, phenol- green). The amount of ferrous sulfate required for each phthalein. Forty ml of boric acid were placed into conical sample for complete combustion was read and recorded. flasks and distilled water added to the 100 ml level. Each Tellen and Yerima Environ Syst Res (2018) 7:3 Page 8 of 29 The difference between the amounts of FeSO added for formation of pedogenic horizons. Hence, a characteristic the samples compared to that added to the blank titration lack of genetic horizons (Fig. 8). determines the amount of combusted carbon. A correc- Yerima (2011) stated that these soils differ in such tion factor of 0.39 was used to account for the incomplete characteristics as texture, effective depth, gravel content, combustion of organic carbon. The percent carbon con - compactness and water infiltration rates. At Ndop, (low tent of the soil samples was then calculated using the fol- altitude), the soils were observed to be rich in alluvial lowing formula proposed by Van Reewijk (2002): deposits and this is corroborated by the fact that Ndop plain is an intermontane basin in the Bamenda High- V 1 − V 2 lands. The soil types observed here include; Inceptisols, % OC = M × × 0.39 × mcf Entisols, and Oxisols. It was suggested that due to these where M the molarity of ferrous sulfate solution (from variations in soil types across elevation, important differ - blank titration), V1 the ml of ferrous sulfate solution ences in physical, chemical and biological characteristics required for blank, V2 the ml of ferrous sulfate solution exist at regional scale. required for sample, S the weight of the air-dry sample in gram, mcf the moisture correction factor, while 0.39 a Effect of LULC change on soil physical properties constant. Table 1 presents the means (± SD) while Table 2 presents a summary of ANOVA for soil MC, BD and particle size Statistical analysis distribution in the soil surface layer (0–15 cm) across dif- The data were analyzed using descriptive and multivari - ferent LULC systems and altitudes. The results for the ate statistics using SPSS version 21.0 for windows. Data individual soil quality attributes include: distributions were checked for normality and then lo g transformed when they were skewed. Pearson’s cor- Soil moisture content (MC) The results also show that relation was used to analyse the relationship between soil moisture content significantly varied with land use selected soil physical and chemical properties. The means types (P  <  0.01) and with elevation (P  <  0.01) (i.e. MC and standard deviations of the selected parameters were increases with increase in altitude (Table 1). Generally, at compared to show their distribution across different land all the elevations, the soils under Eucalyptus saligna plan- use/land cover systems and altitudes in the region. Anal- tation had the highest moisture contents compared to the ysis of variance ratio (ANOVA) was used to test for sig- other land uses/land cover systems except for those under nificant differences between the means, with treatments natural forest land cover systems at the high and low alti- (land use) and group (elevation) set as the independent tudes (Fig. 9). These results corroborate with the findings variables, to determine which parameters varied signifi - of Getachew et al. (2012). cantly with each treatment (Brejda et al. 2000a, b). Soil moisture content (%) at the surface (0–15  cm) showed significant differences (P < 0.01) between the soils Results and discussion of the different land uses/land cover for all the elevation Descriptions and characteristics of soils in the study area (Table 2). At high altitude, the mean soil MC (%) differed In Awing and Santa (high altitude), the soils were pre- significantly (P  <  0.01) between farm and natural forest sumably Inceptisols because they were young soils with only. The study show empty patches with predominantly some colour changes and have rocks at very shallow fern plants under Eucalyptus plantations compared to a depths. In Bamenda (mid-altitude) and at the Yongka dense, continuous layer of undergrowth including Cyno- Park in particular, the soil type varied and was found to don dactylon, Podocarpus sp. found under native forest include: Oxisols, those that possessed loamy and clayey stands (Fig.  10). At mid-altitude, the mean soil MC (%) texture, slightly acidic, contain little or no weatherable under natural savanna forest cover differed significantly minerals, traces of water dispersible clay and extreme (P  <  0.01) from those under E. saligna plantation. Also, weathering of most minerals other than quartz to kao- the mean soil MC (%) under the E. saligna plantation dif- linite and free iron oxides, and have low CEC (< 16 cmol fered significantly (P < 0.01) from those under the affor - (+)/kg); Inceptisols, those that have rocks at vey shal- estation plantations in the Yongka Western Highlands low depth, and were young soils; and Entisols, those that Research Garden Park and grazing land use systems. At lack pedogenic horizons and occur on slopes. The Oxi - low altitude, the mean soil MC (%) under Natural Forest sols presented their characteristic reddish-brown colour, cover differed significantly (P < 0.01) from those under all indicating the presence of oxides of Fe, while Entisols the other land use systems except E. saligna plantation. were observed at the foot of the slope, in areas with fre- Also, the mean soil MC (%) under natural savanna forest quent water saturation and on shoulder slopes where the cover and grazing land use differed significantly (P < 0.01) rate of erosion was presumably higher than the rate of from those under natural forest. Generally, the lower MC Tellen and Yerima Environ Syst Res (2018) 7:3 Page 9 of 29 Fig. 8 Soil profiles showing; Entisol with thin A horizon (a); inceptisol (b); inceptisol with thick A horizon (c) and Entisol exposing stony horizons that constraint plant growth (d) in the North West Region (Source: Yerima (2011)) (%) in soils under E. saligna plantation compared to those Although House (1992) stated that the presence or under natural forest may be due to the observed sparse or absence of understorey is a factor of the density of the absence of undergrowth (Fig. 11). stand and of the rainfall regime, Zerga (2015) reported a In agreement with Aweto and Moleele (2005), the similar finding in Ethiopia and indicated that the domi - sparse or absence of undergrowth and the light canopy nant leaf litterfall under Eucalyptus stands prohibits the of Eucalyptus trees in plantations can lead to higher growth of other plants due to its allelopathic effect. The rate of soil water evaporation, whereas the dense under- latter explained that chemicals from the leaves of Euca- growth in the native forest could lower soil temperature lyptus trees reduce the soil nutrients that are necessary and reduce evaporation to enhance soil water infiltration. for undergrowths, hence, enhancing soil degradation These results also agree with the findings of Cao et  al. through erosion, nutrient and water depletion. It was also (2010) who reported low soil moisture contents, ranging observed in this study that the establishment of euca- from 20.2 to 30.5% in the topsoil (0‒10 cm) under Euca- lyptus plantation not only suppresses undergrowths but lyptus spp. plantations, aged from 3 to 13 years in China. also affects the performance of cultivated crops adjacent The sparse or absence of undergrowth is an indication to the plantation stands, probably due to this allelopathic of reduced biodiversity under Eucalyptus plantations. effects. Tellen and Yerima Environ Syst Res (2018) 7:3 Page 10 of 29 Table 1 Mean (± SD) of soil MC, BD and particle size distribution in the soil layer of 0–15 cm across different land use/ land cover systems and altitudes Soil property Altitude Land use types Virgin forest Virgin savana Farming Park afforesta- Grazing land Eucalyptus P value tion forest a ab b ab ab MC (%) High (> 1500 m) 8.69 ± 0.34 6.96 ± 0.84 5.06 ± 1.33 – 6.96 ± 0.84 6.97 ± 3.31 * ab ac ac ad ce b Mid (900–1500 m) 5.55 ± 1.16 2.78 ± 0.12 3.90 ± 0.85 3.49 ± 0.686 2.42 ± 1.42 5.83 ± 2.02 * a b b b ab Low (< 900 m) 6.98 ± .1.984 2.31 ± 0.83 3.03 ± 1.56 – 2.30 ± 0.83 4.77 ± 0.68 * Total 7.07 ± .1.81 4.01 ± 2.26 3.99 ± 1.41 3.49 ± 0.69 3.90 ± .2.438 5.86 ± 2.51 * 3 a b b b b BD (g/cm ) High (> 1500 m) 0.51 ± 0.03 0.84 ± 0.09 0.89 ± 0.09 – 0.84 ± .009 0.756 ± .151 * a b c bd c bd Mid (900–1500 m) 0.57 ± 0.11 0.87 ± 0.10 1.11 ± 0.24 0.94 ± 0.09 1.19 ± 0.17 0.80 ± .072 * a b c b d Low (< 900 m) 0.79 ± 0.11 1.45 ± 0.00 1.08 ± 0.20 – 1.39 ± 0.08 0.80 ± 0.07 * Total 0.63 ± 0.15 1.05 ± 0.30 1.04 ± 0.21 0.94 ± 0.09 1.14 ± 0.26 0.78 ± 0.11 ab ab b ab ac Sand (%) High (> 1500 m) 28.50 ± 0.58 37.50 ± 1.95 28.38 ± 7.15 – 37.50 ± 1.91 37.0 ± 5.35 * a a a a a a Mid (900–1500 m) 36.50 ± 5.80 34.00 ± 6.93 34.50 ± 4.98 36.92 ± 4.46 32.00 ± 4.97 35.4 ± 9.99 NS ab ab b ab ac Low (< 900 m) 38.00 ± 0.00 37.00 ± 0.00 41.88 ± 5.69 – 31.50 ± 8.43 35.2 ± 6.702 * Total 34.33 ± 5.31 36.17 ± 4.09 34.86 ± 7.67 36.97 ± 4.46 33.67 ± 5.93 36.0 ± 7.427 ab ab b ab ac Silt (%) High (> 1500 m) 57.00 ± 0.00 48.00 ± 2.00 56.13 ± 6.49 – 48.00 ± 2.00 48.0 ± 5.657 * a a a a a a Mid (900–1500 m) 47.00 ± 5.89 52.00 ± 5.77 48.00 ± 5.94 45.50 ± 4.10 53.00 ± 6.93 49.0 ± 10.7 NS ab ab b ab ac Low (< 900 m) 43.00 ± 0.00 47.00 ± 0.00 42.00 ± 5.76 – 51.50 ± 9.15 52.00 ± 5.29 * Total 49.00 ± 6.88 49.00 ± 3.91 48.61 ± 7.98 45.50 ± 4.10 50.83 ± 6.46 49.20 ± 7.81 a a a a a Clay (%) High (> 1500 m) 14.50 ± 0.58 14.50 ± 1.00 15.12 ± 0.99 – 14.50 ± 1.00 14.63 ± 2.77 NS a a a a a a Mid (900–1500 m) 16.25 ± 2.87 13.50 ± 1.73 17.17 ± 2.69 17.25 ± 3.77 14.75 ± 2.75 15.25 ± 2.96 NS a ab ab ab b Low (< 900 m) 18.50 ± 0.58 16.00 ± 0.00 16.00 ± 1.69 – 16.75 ± 2.22 12.7 ± 3.50 * Total 16.42 ± 2.31 14.67 ± 0.50 16.25 ± 2.17 17.25 ± 3.77 15.33 ± 2.18 14.50 ± 2.98 Means in the same row followed by the same letters (a, b or c) are not significantly different at 1% significance NS non significance, MC moisture content, BD bulk density * Significant at P < 0.01 Table 2 Summary of ANOVA for BD, MC, and particle size distribution in relation to land use and elevation Source of variations df BD MC Clay Silt Sand MS P MS P MS P MS P MS P Land use (LU) 5 0.485 0.000 23.725 0.000 17.158 0.023 37.487 0.391 20.638 0.689 Elevation (E) 2 0.653 0.000 71.025 0.000 10.801 0.181 111.44 0.049 55.171 0.197 LU * E 8 0.113 0.000 4.987 0.034 9.176 0.16 124.66 0.002 102.48 0.005 Error 80 0.019 2.246 6.177 35.486 33.329 MS is the mean square, P is the p value, df is degree of freedom Soil bulk density The results also showed that soil bulk and further depicts the altitudinal variations. In terms density significantly varied with land use types (P < 0.01) of absolute values however, the results for this research and across elevation (P < 0.01) with significant interactions showed that soils under farmland had the highest bulk between subject effects (land use and elevation) (P < 0.01) density (0.894 and 1.450  g/cm ), while those under the (Table 2). Generally, at all altitudes, the soil under natural natural forest had the lowest bulk density, (0.517 and 3 3 forest had the lowest bulk density (g/cm ) compared to 0.790 g/cm ) in the top 0–15 cm soil layer at high and low the other land use s/land cover systems, followed by the altitudes respectively. At mid-altitude, soils under graz- soil under E. saligna plantation, while soil under farmland ing land use system had the highest bulk density (1.185 g/ and grazing land had a higher bulk density (Fig. 10). These cm ) while those under the natural forest land cover sys- results corroborate the findings of Getachew et al. (2012) tem had the lowest bulk density (0.570 g/cm ) in the top Tellen and Yerima Environ Syst Res (2018) 7:3 Page 11 of 29 this altitude, bulk density (g/cm ) showed no significant difference between soils under natural savanna and those under farmland, grazing land, and E. saligna planta- tion, respectively. Also, bulk density (g/cm ) showed no significant difference (P  >  0.01) between the soils under farmland and E. saligna plantations. At mid-altitude, bulk density (g/cm ) also showed significant differences (P  <  0.01) between the soils under natural forest and all the other land use/land cover systems except natu- ral savanna and E. saligna plantations. At this altitude, bulk density (g/cm ) showed no significant difference (P  >  0.01) between soils under natural savanna and all other LULC systems except grazing land. At low alti- tude, bulk density (g/cm ) differed significantly (P < 0.01) between the soils under natural forest and all the other Fig. 9 Estimated marginal means of soil moisture content (%) in the land use/land cover systems except those under the E. soil layer of 0–15 cm across different land use/land cover systems and saligna plantation. However, at this altitude, bulk density altitudes (g/cm ) showed no significant difference between soils under natural savanna and those under grazing land. Soil bulk density represents a measure of soil compac- tion and health. Kakaire et al. (2015) stated that a higher soil bulk density means that less amount of water is held in the soil at field capacity, while a lower soil bulk den - sity means soils are less compacted and are able to retain more water. These results corroborate the findings of Ravina (2012) who reported a higher soil bulk density of 1.24  g/cm under Eucalyptus spp. plantation compared to 0.66  g/cm under a native forest in a Brazilian soil (0–15  cm). In addition, Kolay (2000) indicated that bulk density of productive natural soils generally ranges from 1.1 to 1.5 g/cm . Since the soil bulk densities found in all the land uses were lower and within this range, it can be concluded that the soil productivity in the area is good. Furthermore, since the soil bulk densities found in the Eucalyptus plantation, grazing land, and farmland were Fig. 10 Estimated marginal means of bulk density (g/cm ) in the of higher than those under native forest, it can be concluded 0–15 cm soil layer across different land use/land cover systems and that the conversion of forest to Eucalyptus plantations, altitudes farmland and grazing land increases soil bulk densities probably due to increased soil compaction. The find - ings from the study confirm those of Aweto and Moleele 0–15 cm soil layer. It can be suggested that deforestation (2005), who concluded that Eucalyptus spp. plantations and subsequent tillage practices resulted in soil compac- increased soil bulk density more than the native forest in tion, low infiltration and hence increased in bulk density Botswana. for surface soil in North West Region of Cameroon. Simi- lar finding has been reported in other areas around the Particle size distribution Although not significant, the world (Getachew et al. 2012; Javad et al. 2014). results show that particle size distribution varied with Nonetheless, bulk density (g/cm ) showed a significant LULC systems across the different altitudes. However, the difference (P  <  0.01) at all altitudes, between the soils of interactions between subject effects were only significant the different land uses/land cover system for the surface (P < 0.01) for sand and silt contents (Table 2). 0–15  cm soil layer (Table  1). At high altitude, bulk den- sity (g/cm ) differed significantly (P  <  0.01) between the Sand content soils under natural forest and all the other land use/land At high altitude, the soils under both natural savanna and cover systems except E. saligna plantations. However, at grazing land use systems had the highest percentage of Tellen and Yerima Environ Syst Res (2018) 7:3 Page 12 of 29 Fig. 11 Eucalyptus plantation showing sparse undergrowth (a); absence of undergrowth with light canopy (b); native forest showing dense under- growth (c); dark forest canopy with mushroom growing on plant remains (d) sand content (37.5%), while those under natural forest and cropland had the lowest (28.5 and 28.4%, respec- tively) (Fig.  12). This is probably due to the fact that there was no existing land uses where savanna vegeta- tion was protected against disturbance either by burn- ing or grazing in the area. The lower sand content under farmland may be attributed to tillage practices and dif- ferential segregation by erosion on inceptisols. However, at this altitude, mean percentage sand content at the sur- face (0–15  cm) layer showed no significant difference (P  >  0.01) between the soils under all the land use/land cover systems. At mid-altitude, the soils under afforesta - tion land use systems in the Yongka Park had the high- est percentage of sand content (36.9%) while those under grazing land had the lowest (32%). Although the graz- Fig. 12 Estimated marginal means of sand (%) in the 0–15 cm soil ing land had low sand proportions at this altitude, mean layer across different land use/land cover systems and altitudes percentage sand content at the surface (0–15  cm) layer showed no significant difference (P  >  0.01) between the Tellen and Yerima Environ Syst Res (2018) 7:3 Page 13 of 29 soils under all the land use/land cover systems. This can indicator for evaluating soil degradation under different be due to the fact that the soils are oxisols, originating land use systems. from a granitic parent material, characterized by colloidal fractions and dominated by low activity clays and sesqui- Silt content oxides (Yerima and Van Ranst 2005b). At high altitude, the soils under the natural forest land The soils under afforestation land use system in the cover system had the highest percentage of silt content park are varied, which is probably a representation of the (57%), while those under farmland was intermediate different stages of soil development. The park area was (56%) (Fig. 14). Those under the natural savanna, grazing formerly a grazing land, with an unstable geomorphic land and E. saligna plantation had the lowest percentages surface, which resulted in soil erosion and exposure. The and of equal values (48%). However, at this altitude, mean gullies observed under the afforestation stand with Arto - percentage silt content at the surface (0–15  cm) layer carpus heterophyllus (Jackfruit) is associated with the showed no significant difference (P  >  0.01) between the concentration of runoff water from the road (Fig. 13). soils under all the LULC systems. At low altitude, the soils under farmland had the It was noticed that the area under natural savanna highest percentage of sand content (41.9%) while those forest cover at high altitude was also used for grazing. under grazing land use systems had the lowest (31.5%). The frequent burning of grass during the dry season by Again, at this altitude, mean percentage sand content at the surface (0–15  cm) layer showed no significant dif - ference (P  >  0.01) between the soils under all the land use/land cover systems. There was no existing land uses where natural forest cover and savanna vegetation was protected against disturbance either by burning or graz- ing in this area. Therefore there were high similarities with nonsignificant differences in soil properties under the different land uses in this area. Generally, the results showed that sand content increased when converting natural forest to cropland, and this is most likely resulting from the preferential removal of clay and silt and residual accumulation of sand in soil surface resulting from pref- erential segregation and evacuation of the smaller silt and clay particles, by accelerated water erosion. These results are in agreement with the findings of Javad et  al. (2014) who attesting to the results of Ayele et al. (2013) reported Fig. 14 Estimated marginal means of silt (%) in the 0–15 cm soil layer that sand content is a physical parameter affected by across different land use/land cover systems and altitudes soil erosion and, hence, can be measured and used as an Fig. 13 Artocarpus heterophyllus afforested stand (a); gully erosion under the Artocarpus heterophyllus stand (b) Tellen and Yerima Environ Syst Res (2018) 7:3 Page 14 of 29 cattle herdsmen and trampling effects due to overgraz - ing is suggested to have influence soil structure as burn - ing destroys and removes soil organic matter, thereby loosening of soil particles and encouraging water ero- sion on gentle slopes. In addition, the E. saligna planta- tion here was located on steep slopes, with abundant leaf litter and no vegetation understory. It can be suggested that the silt content under natural savanna, grazing land and E. saligna plantation were lower due to accelerated water erosion. The lack of ground cover and understory may have contributed to initiating erosion which selec- tively washes away clay and silt. At mid-altitude, the soils under grazing land use systems had the highest percent- age of silt content (53%) while those under the afforesta - tion land use projects in the Yongka Park had the lowest Fig. 15 Estimated marginal means of clay (%) in the 0–15 cm soil percentage (47%). At this altitude, mean percentage silt layer across different land use/land cover systems and altitudes content at the surface (0–15  cm) layer showed no sig- nificant difference (P  >  0.01) between the soils under all the land use/land cover systems. The soils under the natural savanna land cover had the lowest percentage afforestation stand were located on the shoulder of the (13.5%). At this altitude, mean percentage clay content at slope and signs of severe erosion (rills and gullies) were the surface (0–15 cm) layer showed no significant differ - observed, compared to those of grazing land. Geologi- ence (P > 0.01) between the soils under all the land use/ cally, on a midslope, the rate of soil erosion is increased land cover systems. At low altitude, the soils under the and the topsoil layer is greatly reduced. At low altitude, natural forest land cover system had the highest percent- the soils under the E. saligna plantation had the highest age of clay content (18.5%) while those under E. saligna percentage of silt content (52%) while those under farm- plantation had the lowest (12.8%). At this altitude, mean land use systems had the lowest (42%). At this altitude, percentage clay content at the surface (0–15  cm) layer mean percentage silt content at the surface (0–15  cm) showed no significant difference (P  >  0.01) between the layer showed no significant difference (P > 0.01) between soils under all the land use/land cover systems. However, the soils under all the land use/land cover systems. Here the percentage clay content was relatively lower than the soils under the E. saligna plantation were located on those of sand and silt in all the land use/land cover sys- the toe slope (flat surface) and signs of severe deposition tems across the different altitudes. When fine particles (siltation, floods and stagnant water bodies) were gener - of soils are high, EC may increase. However, increased ally observed in the area after heavy rainfall. Geologically, EC in soils is predominantly due to the presence of solu- on the toe slope, the rate of soil erosion is minimal and ble salts (Yerima and Van Ranst 2005a), but which is not the topsoil layer is mostly comprised of mineral deposits found in the study area, and this may cause instability of transported principally by water (erosive agent) from top soil structure. and shoulder slopes. However, soils under farmland use systems are prone to erosion comparatively. Soil texture Generally, the results show that the soil tex- ture in the study area ranged from loam to silt loam, which Clay content is very good for agriculture. Specifically, the result shows The result shows that at high altitude, the soils under that on one hand, the soil texture under natural vegeta- farmland use system had the highest percentage of clay tion cover and farmland use systems in the NW region content (15%), while those under E. saligna plantation changed from silt loam to loam, as elevation decreases was intermediate (14.6%) (Fig. 15). Those under the natu - (Table 3). On the other hand, the soil texture under graz- ral savanna, natural forest, and grazing land had the low- ing land use system and E. saligna plantation changed est percentages and of equal values (14%). At this altitude, from loam to silty loam as elevation decreases. This is sug - mean percentage clay content at the surface (0–15  cm) gested to be due to pedogenic processes including degra- layer showed no significant difference (P > 0.01) between dation (surficial erosion) and aggradation (cumulization) the soils under all the land use/land cover systems. (Yerima and Van Ranst 2005a). At mid-altitude, the soils under the afforestation land Ideally, the conversion of forest into cropland is known use projects in the Yongcak Park had the highest per- to deteriorate soil physical properties and making the centage of clay content (17.3%) while those under the Tellen and Yerima Environ Syst Res (2018) 7:3 Page 15 of 29 Table 3 Soil texture in the 0–15 cm soil layer across different land use/land cover systems and altitudes Soil property Altitude Land use types Virgin forest Virgin savana Farming Park afforestation Grazing land Eucalyptus forest Texture High (> 1500 m) Silt loam Loam Silt loam – Loam Loam Mid (900–1500 m) Loam Silt loam Loam Loam Silt loam Loam Low (< 900 m) Loam Loam Loam – Silt loam Silt loam land more susceptible to erosion since soil structure Effects of land use change on soil chemical properties (macroaggregates) is disturbed. Soil erosion can mod- Generally, the chemical properties of soils show vari- ify soil properties by reducing soil depth, changing soil ations under the different land uses across the differ - texture, and by the loss of nutrients and organic matter ent altitudinal zones of the study area. Table  4 presents (Lobe et al. 2001). the mean (±  SD) while Table  5 present the summary of Table 4 Mean (± SD) of soil pH, SOC, TN, and Av.P in the 0–15 cm soil layer across different land use/land cover systems and altitudes Soil property Altitude Land use types Virgin forest Virgin savana Farming Park afforestation Grazing land Eucalyptus forest ANOVA pH H O High 5.35 ± .288 5.90 ± 0.20 5.21 ± 0.538 5.90 ± 0.200 5.57 ± 0.183 * Mid 5.63 ± 0.125 5.65 ± .057 5.48 ± 0.540 5.70 ± 0.159 6.10 ± .316 5.56 ± 0.130 * Low 6.50 ± 0.230 6.50 ± .000 5.87 ± 0.205 6.00 ± .496 5.77 ± 0.221 * Total 5.82 ± 0.551 6.02 ± .380 5.51 ± 0.520 5.70 ± .159 6.00 ± 0.335 5.61 ± 0.183 pH KCl High 4.45 ± o.288 4.65 ± 0.06 4.34 ± 0.27 4.65 ± 0.06 4.36 ± 0.23 * Mid 4.65 ± 0.10 4.50 ± 0.00 4.58 ± 0.06 4.46 ± 0.12 4.60 ± 0.22 4.56 ± 0.11 * Low 5.55 ± 0.17 5.30 ± 0.00 5.01 ± 0.32 4.88 ± 0.30 4.58 ± 0.15 * Total 4.88 ± 0.53 4.81 ± 0.36 4.63 ± 0.34 4.46 ± 0.12 4.71 ± 0.23 4.49 ± 0.19 Δ pH High − 0.90 ± 0.00 − 1.25 ± 0.17 − 0.88 ± 0.37 − 1.25 ± 0.17 − 1.21 ± 0.25 Mid − 0.98 ± 0.15 − 1.15 ± 0.06 − 0.91 ± 0.56 − 1.24 ± 0.14 − 1.50 ± 0.34 − 1.00 ± 0.16 Low − 0.95 ± 0.06 − 1.20 ± 0.00 − 0.86 ± 0.18 − 1.25 ± 0.38 − 1.20 ± 0.16 Total − 0.94 ± 0.09 − 1.20 ± 0.10 − 0.89 ± 0.41 − 1.24 ± 0.14 − 1.29 ± 0.32 − 1.13 ± 0.22 SOC (%) High 6.50 ± 1.62 4.83 ± 0.36 3.31 ± 0.57 4.83 ± 0.36 5.79 ± 2.11 * Mid 4.58 ± 1.61 2.10 ± 1.15 3.04 ± 0.87 2.83 ± 0.88 2.50 ± 0.83 3.46 ± 0.95 * Low 3.10 ± 0.81 3.10 ± 0.00 1.83 ± 0.90 1.90 ± 1.18 3.05 ± 0.53 * Total 4.73 ± 1.93 3.34 ± 1.33 2.77 ± 0.99 2.83 ± 0.88 3.08 ± 1.52 4.31 ± 1.89 C/N ratio High 21.91 ± 0.76 14.58 ± 2.39 13.06 ± 4.50 14.58 ± 2.39 24.74 ± 15.25 Mid 16.95 ± 8.63 9.10 ± 3.82 17.68 ± 6.53 12.05 ± 4.76 13.37 ± 6.31 17.36 ± 7.18 Low 11.18 ± 3.34 23.85 ± 0.00 8.65 ± 3.94 11.13 ± 9.31 14.00 ± 4.18 Total 16.68 ± 6.67 15.84 ± 6.78 13.78 ± 6.43 12.05 ± 4.76 13.03 ± 6.18 19.64 ± 11.28 TN (%) High 0.30 ± 0.06 0.34 ± 0.07 0.27 ± 0.06 0.34 ± 0.06 0.27 ± 0.11 * Mid 0.29 ± 0.08 0.22 ± 0.03 0.18 ± 0.03 0.25 ± 0.07 0.20 ± 0.03 0.21 ± 0.05 Ns Low 0.28 ± 0.01 0.13 ± 0.00 0.21 ± 0.05 0.19 ± 0.06 0.23 ± 0.04 Ns Total 0.29 ± 0.05 0.23 ± 0.09 0.21 ± 0.06 0.25 ± 0.07 0.24 ± 0.08 0.24 ± 0.08 Av.P (ppm) High 16.1 ± 3.00 19.1 ± 13.3 20.1 ± 10.3 19.1 ± 13.3 13.4 ± 7.19 Ns Mid 14.6 ± 3.74 15.6 ± 4.91 15.5 ± 7.65 9.83 ± 3.53 9.33 ± 4.16 11.1 ± 4.31 Ns Low 13.3 ± 2.25 5.30 ± 0.00 13.2 ± 5.61 8.90 ± 2.40 11.9 ± 2.39 Ns Total 14.6 ± 3.02 13.3 ± 9.59 16.1 ± 8.17 9.83 ± 3.53 12.4 ± 8.87 12.2 ± 5.28 Means in the same row followed by the same letters are not significantly different at 1% significance Ns non significance, MC moisture content, BD Bulk density * Significant at P < 0.01 Tellen and Yerima Environ Syst Res (2018) 7:3 Page 16 of 29 Table 5 Summary of ANOVA for pH, SOC, TN, and available P in relation to land use and elevation Source of variations df Av.P SOC TN C:N ratiopH H O MS P MS P MS P MS P MS P Land use (LU) 5 71.178 0.167 8.659 0.000 0.010 0.018 96.951 0.076 0.669 0.000 Elevation (E) 2 302.101 0.002 40.292 0.000 0.065 0.000 103.16 0.116 1.943 0.000 LU * E 8 39.388 0.892 2.539 0.035 0.008 0.027 149.80 0.003 0.286 0.008 Error 80 44.179 1.14 0.004 46.552 0.101 MS in the mean square, P is the p value, df is degree of freedom ANOVA for soil pH, SOC, TN, and Av.P in the 0–15 cm soil layer across different LULC systems and altitudes in the study area. Effects of land use change on soil pH H O, pH KCl and Δ pH The results also showed that soil pH significantly varied with land use types (P < 0.01) and across elevation (P  <  0.01) with significant interaction between subjects effects (P  <  0.01) (Table  4). According to Landon (1991) ratings, the soil pH for all the land uses in this study were low to medium (slightly acidic), probably due to the par- ent material (granitic) which is acidic in nature and are characteristic of oxisols. The results show that the soil under farmland use had relatively lower pH H O and pH KCl values and lower net charges compared to those of the other land uses/land cover systems in the area. In gen- Fig. 17 Estimated marginal means of pH KCl values in the 0–15 cm eral, soil pH decreased with increase in altitude (Figs. 16, soil layer across different land use/land cover systems and altitudes 17 and 18). This may be largely due to the use of chemical fertilizers including urea, potash, and N, K, P (20:10:10), as well as the high use of weedicides such as roundup, by farmers in the area which contain high amounts of cations that helps to neutralise the negative charges. The results show that there is a net negative charge for all the soils in Fig. 18 Estimated marginal means of net charge (Δ pH) values in the 0–15 cm soil layer across different land use/land cover systems and altitudes the area under study. The weathering of the granitic par - Fig. 16 Estimated marginal means of pH H 0 values in the 0–15 cm ent material, which results in iron and aluminum oxides, soil layer across different land use/land cover systems and altitudes as well as leaching of more soluble soil minerals and basic Tellen and Yerima Environ Syst Res (2018) 7:3 Page 17 of 29 cations, may have caused the slight acidity of the soils in soil, with increased efficiency as altitude increases, in the the study area. The net charge was less negative under North West Region of Cameroon. This result contradicts native forest systems compared to grazing, savanna, Euca- the findings of Kizilkaya and Dengiz (2010) who reported lyptus plantation and afforestation systems. a significant increase of pH from 6.03 in soils under natu - At high altitude, the soils under farmland use system ral forest to 7.71 in soils under cultivated land in Turkey. had the lowest mean pH value (5.2) while those under Although these are two different environments, this dif - natural savanna and grazing land had the highest mean ference may be due to the fact that sustainable agricul- pH value (5.9). At this altitude, mean pH values at the tural land management practices such as the application surface (0–15  cm) layer showed a significant difference of organic manure, mulching, rotation and limited tillage (P  <  0.01) between the soils under natural forest and were adopted in the cultivated land in Turkey while those natural savanna, as well as between those under farm- in our study area did not adopt sustainable land manage- land, natural savanna and grazing land use systems. The ment practices. It could also be due to the high basic fer- results also show that the soils under natural forest cover tilizer applications. Low soil pH impeds the CEC of the and E. saligna plantation had a relatively lower pH val- soil by altering the surface charge of colloids (finest clay ues (pH < 5.5) in this area. This is because Low pH slows particles and soil organic matter) (McCauley et al. 2005). down the breakdown of litter due to low microbiological Low CEC implies that soil will have less exchangeable activity (Yerima and Van Ranst 2005a). cations required as crop nutrients, nutrients are weekly Similarly, at mid-altitude, the soils under farmland use adsorbed and hence may be leached out. systems had the lowest mean pH value (5.4) followed by those under E. saligna plantation (5.5), while those under Effects of  land use change on  soil organic carbon (SOC) natural savanna and grazing land had the highest mean and organic matter (SOM) The results also showed that pH value (6.1). This similarity in pH values can be due SOC significantly varied with land use types (P < 0.01) and to the fact that the land use under natural savanna was with elevation (P < 0.01) but the interaction between sub- also used for cattle grazing. At this altitude, mean pH jects effects was not significant (P >  0.01) (Table  5). Fol- values at the surface (0–15  cm) layer showed a signifi - lowing the ratings by Yerima and Van Ranst (2005a), the cant difference (P  <  0.01) between the soils under farm - results show that all the soils under the different land use land and grazing land use systems, as well as between systems across the different elevations were medium to soils under E. saligna plantation and grazing land use high in SOC content. However, the percentage of OC con- system. The relatively high pH values under grazing centration for soils under natural forest as well as those land may be due to the high cow dung wastes depos- under E. saligna plantations were higher compared to all ited on the fields. Interestingly, at low altitude, the soils the other land use systems at all elevations (Fig.  19). In under E. saligna plantation had the lowest mean pH addition, the results indicate that OC in soils increased value (5.7) while those under natural forest and natural with increase in elevation in the N.W region. These results savanna had the highest mean pH value (6.5). Humphrey corroborate the findings of Yerima and Van Ranst (2005a). and Amawa (2014) also reported a similar finding in the study area. At this altitude, mean pH values at the surface (0–15 cm) layer showed a significant difference (P < 0.01) between the soils under natural vegetation (forest and savanna) cover and those under farmland and E. saligna plantation. Generally, the slightly acidic nature of the soils under all the land use/land cover systems may be due to the weathering of granitic parent materials and the intense leaching of basic cations. Also, the low pH values in farm- land could be due to high tillage frequency, high rates of inorganic fertilizer applications (especially ammonium fertilizers), low amount of organic matter as a result of erosion or due to aluminum toxicity. In fact, the sig- nificant differences of mean pH values at the surface (0–15 cm) layer between soils under cultivated land and those under natural vegetation across different altitudes Fig. 19 Estimated marginal means of soil organic carbon (%) in the indicates that the conversion of natural vegetation cover 0–15 cm soil layer across different land use/land cover systems and altitudes (forest and savanna) to farmland decreases pH of the Tellen and Yerima Environ Syst Res (2018) 7:3 Page 18 of 29 At high altitude, the soils under natural forest land matter mineralization associated with low temperatures cover system (protected forest) had the highest mean soil and decrease microbial activity. organic carbon content (6.50%) followed by those under At mid-altitude, the soils under natural forest land E. saligna plantations (5.79%) (Table  4). Those under cover systems still had the highest mean SOC content farmland use systems had the lowest mean percent- (4.58) followed by those under E. saligna plantation age of soil organic carbon content (3.31%). At this alti- (3.46%) (Table 4). Although the mean percentage of SOC tude, the mean percentage of SOC content at the surface contents for soils under farmland use systems were low (0–15 cm) layer showed a significant difference (P < 0.01) (3.04%), those under the natural savanna land use sys- between the soils under natural forest and farmland. tems had the lowest mean percentage (2.10%) compared Also, the results showed a significant difference (P < 0.01) to all the other land use/land cover systems. However, at between the soils under E. saligna plantations and those this altitude, the mean percentage of SOC content at the under farmland. However, there were no significant dif - surface (0–15  cm) layer showed significant differences ferences (P  >  0.01) between soils under natural savanna (P  <  0.01) between the soils under natural forest cover and grazing land. This may be due to the fact that the nat - and savanna, afforestation, and grazing land use systems. ural savanna land cover systems were observed to be sub- Although the natural savanna land cover system was jected to conditions similar to grazing land use (burning within the Yongka Garden Park, the results showed that and cattle grazing) in the area (Fig. 20). More so, the rela- the soil was low in soil organic carbon content compared tively higher soil organic carbon contents at higher eleva- to those under the natural forest cover. This can be sug - tions may be due to a slow down in the rate of organic gested to be due to the fact that the land was previously Fig. 20 Sheep and cattle grazing on grazing land (a); cattle grazing on Eucalyptus plantation (b); fire disturbance on grazing land (c); burnt tree trunks showing evidence of fire disturbance on Eucalyptus plantation (d) Tellen and Yerima Environ Syst Res (2018) 7:3 Page 19 of 29 used for cattle grazing, and soils in the area were gener- content compared to native ecosystems, since cultivation ally low in organic matter before the establishment of increases aeration of soil, which enhances decomposition the park (9 years old, after many years of cattle grazing), of soil organic matter (Kizilkaya and Dengiz 2010). due to unsustainable land use practices and soil degrada- These results conform to the assertion that SOC stocks tion. Results from interview with researchers from the are sensitive to land use and cover change (Guo and Gif- park, on the land use history of the area reveals that after ford 2002; Wiesmeier et al. 2012) probably because of the several years of intensive exploitation, prior to the estab- alterations of both carbon inputs (amount and quality lishment of the Park, mining of the soil organic carbon of litter mass) and losses (decomposition and minerali- and nutrient stocks was an issue, which led to a decline zation). Soil carbon improves the physical properties of in fertility, compaction of surface soils and slow and soil, increases the cation exchange capacity (CEC) and poor regeneration of vegetation on land left for fallow. water-holding capacity of the soil, and contributes to the They added that issues of water and fuelwood scarcity structural stability of soils by helping to bind particles in the nearby community were prominent at the time. into aggregates (Leeper and Uren 1993). It can be sug- This result is in line with the findings of Humphrey and gested that, anthropogenic activities that accentuate SOC Amawa (2014), who stated that intensification of agri - loss in the soil including tillage (hoeing, plowing), bio- culture and the use of inappropriate cultural practices mass burning, residual removal, overgrazing, and drain- including the cultivation on fragile (steep) hill-slopes, age, are responsible for the distribution of SOC contents setting of bushfires, overgrazing by cattle, building of observed, at different elevations, under the different land settlements, and increased consumption of the regions use/land cover systems in the N.W region. fuelwood, has lead to environmental and soil degradation Since carbon is a fundamental constituent of soil in the area. In fact, Yerima (2011) elucidated that soils in organic matter (Ogle et  al. 2005), the trends in effects the park are acidic in nature, have low nutrient contents of soil organic carbon under the different land use/land with compact and dense structures that are an impedi- cover systems in the N.W region mirrors that of SOM ment to plant growth. These are tangible reasons attract - and hence carbon storage of soil. It is well recognized ing afforestation initiatives and other sustainable land that SOM increases structural stability, resistance to use practices that promote conservation of biodiversity rainfall impact, the rate of infiltration and faunal activi - in the area. Hence, it is unarguable that the SOC values ties (Roose and Barthes 2001). SOM, of which carbon is reported in this study only presents a picture of the ongo- a major part, holds a great proportion of nutrients cati- ing land regeneration efforts that may require a longer ons and trace elements that are of importance to plant period of time to show its actual image. growth. According to Leu (2007), it prevents nutrient At low altitude, the soils under natural forest and those leaching and is integral to the organic acids that make under natural savanna land cover systems had the high- nutrients accessible to plants while acting as a soil buffer est mean soil organic carbon content (3.10%) followed to resist strong changes in pH. It is widely accepted that by soils under E. saligna plantations (3.05%) (Table  4). the carbon content of soil is a key element in its overall Those under farmland use systems had the lowest mean health (Yerima and Van Ranst 2005a). percentage of soil organic carbon content (1.83%). How- ever, at this altitude, the mean percentage of soil organic Effects of land use change on soil total nitrogen Soil total carbon content at the surface (0–15 cm) layer showed no nitrogen is typically used as an important index for soil significant differences (P > 0.01) between the soils under quality evaluation and reflects the soil nitrogen status all the land use/land cover systems. This can be attributed (Sui et al. 2005). Similar to soil organic carbon, soil total to the higher soil temperatures, which increases the rate nitrogen content (%) also exhibited obvious differences of mineralization due to increase in microbial activity. In at the surface (0–15  cm) layer under different land use/ addition, the area is located at the toe slope where the dif- land cover systems across the three elevations (Table  4). ference in slope gradient influences erosion, flooding and The results also showed that soil total nitrogen did not subsequent deposition of inorganic materials downslope. vary significantly with land use types (P < 0.01), but var - Deposition of inorganic materials through erosion bur- ied significantly with elevation (P  <  0.01). However, the ies the topsoil which is normally rich in organic matter, interaction between subjects’ effects was not significant hence the true picture of soil organic carbon is blurred (P < 0.01) (Table  4). Generally, the results show that soil at low altitude. As the soils under natural savanna were total nitrogen contents increase with an increase in eleva- subjected to grazing practices, it is possible that the soil tion in the N.W region (Fig. 21). samples collected were influenced by animal waste dep - The study showed that at high altitude, both the soils osition, hence the high SOC value recorded. Further- under savanna and grazing land use systems had the more, cultivated soils generally have low organic matter highest mean soil total nitrogen content (0.36%) followed Tellen and Yerima Environ Syst Res (2018) 7:3 Page 20 of 29 the surface (0–15 cm) layer showed no significant differ - ence (P > 0.01) between the soils under all the land use/ land cover systems. Although the level of nitrogen ferti- lizer use as agric-input was high in the region, the total nitrogen contents are low in farms, probably because of the poor nitrogen retention ability of the soils under farmland uses and the loss of organic matter which is a source of nitrogen. At low altitude, the soils under natural forest land cover systems also had the highest mean soil total nitrogen content (0.28%), while those under savanna land use had the lowest values (0.19%). At this altitude, mean soil total nitrogen at the surface (0–15  cm) layer showed significant differences (P  <  0.01) only between the soils under natural forest vegetation and those under natural savanna land cover systems. This can be due to Fig. 21 Estimated marginal means of nitrogen (%) in the 0–15 cm the fact that soils under savanna cover were disturbed by soil layer across different land use/land cover systems and altitudes human activities including; burning and grazing, which greatly influence the soil organic matter and hence soil nitrogen content. by those under natural forest cover (0.30%), while those under farmland system had the lowest. At this altitude, Effects of  land use change on  soil C/N ratio The results mean soil total nitrogen at the surface (0–15  cm) layer also show that the C/N ratio had no significant differences showed no significant difference (P  >  0.01) between the with land use types (P > 0.01) and with elevation (P > 0.01) soils under all the land use/land cover systems. It was but the interaction between subjects effects was signifi - observed that pasture density under grazing land use cant (P  <  0.01) (Table  4). However, the results indicate systems at the higher altitude was higher compared to an increase in C/N ratio with an increase in elevation in that at lower altitudes. This has a direct relationship with the N.W region except for soils under savanna and farm- organic matter content. Again, the similarities in results land use systems (Fig.  22). The quality of organic matter between savanna and grazing land may probably be due is expressed in form of the C/N ratio. According to rat- to the similarities in observed conditions (burning and ings by Yerima and Van Ranst (2005a), the results show cattle grazing) under the two land use systems in the that the quality of organic matter in all the soils under the area. The high amounts of nitrogen in soils under graz - different land use systems across the different elevations ing land may be due to the burning of grass that produce ranged between good quality, medium, and low quality. At ash which is rich in nitrogen and other major nutrients. It high altitude, the mean C/N ratio for soils under natural is well known that fire simulates cycling of nitrogen and thus, relatively high amounts of nitrogen in the ash could be found under such disturbed land use sites. Grazing land is also subjected to deposition of cow dung waste, which enhances the soil organic matter content. A high soil organic matter content strongly correlates with high nitrogen content. However, strong fires on sandy soils may give long-lasting loss of soil surface humus and nitrogen, which may lead to site impoverishment. Also, studies have suggested that grazing can promote nutri- ent cycling because livestock feces and urine provide large amounts of soluble nitrogen that is readily avail- able to plants for growth and livestock excretions can promote soil organic matter (SOM) mineralization rates (McNaughton et al. 1997). At mid-altitude, the soils under natural forest land cover system had the highest mean soil total nitrogen content (0.29%) while those under farmland had the low- Fig. 22 Estimated marginal means of C/N ratio in the 0–15 cm soil est (0.18%). At this altitude, mean soil total nitrogen at layer across different land use/land cover systems and altitudes Tellen and Yerima Environ Syst Res (2018) 7:3 Page 21 of 29 forest, savanna, and grazing land, as well as those under E. saligna plantations, reveals that the quality of organic matter was low (C/N > 14). Only soils under farmland had the medium quality of organic matter (C/N = 10–14). At mid-altitude, the mean C/N ratio for soils under savanna forest cover reveals that the organic matter was of good quality (C/N  <  10), while those for soils under afforestation plantations and grazing systems were of medium quality (C/N  =  10–14). However, those under natural forest, farmland and E. saligna plantations reveal that the quality of organic matter was low (C/N > 14). At low altitude, the mean C/N ratio for soils under farm- land reveals that the quality of organic matter was good (C/N  <  10), while those for soils under natural forest, E. saligna plantations and grazing land were of medium quality (C/N  =  10–14). However, those under natural Fig. 23 Estimated marginal means of available phosphorus (ppm) in the 0–15 cm soil layer across different land use/land cover systems forest cover reveals that the quality of organic matter was and altitudes low (C/N > 14). Soil C/N ratio is a sensitive indicator of soil quality. The soil C/N ratio is usually considered as an indicator at the surface (0–15 cm) layer showed no significant dif - of soil nitrogen mineralization ability. High C/N ratios ference (P  >  0.01) between the soils under all the land in soils can retard the rate of organic matter and organic use/land cover systems. These results are consistent with nitrogen decomposition by limiting the ability of soil the findings of Awdenegest et al. (2013). microbial actions, whereas low C/N ratios in soils could At mid-altitude, the soils under natural savanna, and accelerate the process of microbial decomposition of those under farmland had the highest mean soil avail- organic matter and nitrogen. However, Wu et  al. (2001) able phosphorus concentrations (15.6 and 15.5  ppm, reported that low soil C/N ratio is not conducive to car- respectively), while those under natural forest and E. bon sequestration. Therefore, it can be concluded that saligna plantation land cover systems were intermediate soils under natural forest, grazing land, and E. saligna (14.6 and 11.1  ppm, respectively). Those under affores - plantations slow down the decomposition rate of organic tation and grazing land use had the lowest values (9.83 matter and organic nitrogen by limiting the soil micro- and 9.33  ppm, respectively). It can be concluded here bial activity ability and can best sequester carbon in the that residue ash may have enhanced the P concentra- region as a means to combat climate change. tions under natural savanna, and those under farmland because burning was a cultural phenomenon under Effects of  land use change on  soil available phospho - these land use systems in the area. Also, the application rus Though not significant, the soil available phos - of chemical P-fertilizers and organic manure (poultry phorus also exhibited obvious differences at the surface manure and cow dung) may have enhanced the P con- (0–15 cm) layer under different land use/land cover sys - centrations in selected farmlands in this area. At this alti- tems (Table 4). However, the results indicate that concen- tude, mean soil available phosphorus concentrations at trations of soil available phosphorus varied significantly the surface (0–15 cm) layer showed no significant differ - (P  <  0.01) with elevation, indicating a decrease with a ence (P > 0.01) between the soils under all the land use/ decrease in elevation in the N.W region (Fig. 23) although land cover systems. the interaction effect between subjects was not significant At low altitude, the soils under natural savanna, and (P > 0.01). those under farmland had the highest mean soil available The study showed that at high altitude, the soils under phosphorus concentrations (15.6 and 15.5  ppm, respec- farmland use systems had the highest mean soil available tively), while those under natural forest land cover were phosphorus concentrations (20.1 ppm) followed by those intermediate (14.6  ppm), while those under savanna under savanna and grazing land use system (19.1  ppm), land use had the lowest values (5.30  ppm). At this alti- while those under E. saligna plantation land use had the tude, mean soil available phosphorus concentrations at lowest value (13.4 ppm) (Table 4). This can be due to the the surface (0–15  cm) layer showed no significant dif - fact that farmers applied fertilizers such as Diammonium ference (P  >  0.01) between the soils under all the LULC phosphate (DAP) on their farmlands. However, at this systems. It is suggested that the relatively lower available altitude, mean soil available phosphorus concentrations Tellen and Yerima Environ Syst Res (2018) 7:3 Page 22 of 29 phosphorus concentrations in the protected forest and E. saligna plantations at all elevations may be related to phosphorus fixation due to the relatively higher organic matter concentrations under these land use systems. This result agrees with the findings of Yimer et al. (2008) who reported higher concentrations of P in soils of the native forest than those of cropland and grazing in the Bale Mountains of Ethiopia. According to ratings by Yerima and Van Ranst (2005a), available phosphorus across all land uses was very low, except those in the top 0–15  cm soil layer of farmlands, at high altitude which was low. In addition, the avail- able phosphorus in soils under all the land uses in the study area falls below the medium sufficiency range of 26–54  mg/kg suggested by Carrow et  al. (2004). The available phosphorus deficiency in soils of our study Fig. 24 Estimated marginal means of cation exchange capacity in area may be due to the inherent low-P status of the par- the 0–15 cm soil layer across different land use/land cover systems and altitudes ent material and erosion loss. This may also be due to the low soil pH which causes P-fixation. These results con - firm the findings of Yerima and Van Ranst (2005b) who under afforestation in the park had the lowest values reported that the available phosphorus in most soils of (19.7  cmol (+)/kg soil). Also, at this altitude, mean con- the North West region is low due to P-fixation, crop har - centration of CEC of soils at the surface (0–15 cm) layer vest, and erosion by water. showed no significant difference (P  >  0.01) between the soils under all the land use/land cover systems. Effects of  land use change on  cation exchange capacity At low altitude, the soils under savanna land cover (CEC, cmol (+)/kg soil) CEC also exhibited some differ - systems had the highest mean CEC concentration ences at the surface (0–15 cm) layer under different land (34.1  cmol (+)/kg soil) followed by those under natural use/land cover systems, although not significant. Also, forest (24.0  cmol (+)/kg soil) while those under farming there were no significant differences (P > 0.01) with eleva - land use systems had the lowest values (17.7  cmol (+)/ tions and the interaction between subjects effects was not kg soil). At this altitude, mean CEC concentration of significant (P < 0.01) (Table  4). Generally, the results did soils at the surface (0–15  cm) layer showed a significant not show a clear picture of the variation of CEC of soils difference (P  <  0.01) only between the soils under natu - under different land use/land cover systems with eleva - ral savanna vegetation cover and farmland use systems. tion, in the N.W region (Fig. 24). Generally, according to ratings by Landon (1991), the The study shows that at high altitude, both the soils CEC values in soils under all the land use/land cover sys- under savanna and grazing land use systems had the tems, were medium except those under natural forest and highest mean concentration of CEC (23.1  cmol (+)/ savanna land use cover at mid and low elevations, respec- kg soil), followed by those under farmland (19.7  cmol tively which were high. (+)/kg Soil), while those under E. saligna plantation and natural forest cover were relatively lower (17.6 and Effects of land use change on electrical conductivity (mS/ 16.3  cmol (+)/kg soil, respectively) (Table  4). However, cm) EC values ranged from 0.05 mS/cm under grazing at this altitude, mean CEC concentration of soils at the land use systems to 0.18 mS/cm under natural forest veg- surface (0–15 cm) layer showed no significant difference etation. Generally, the results show that EC varied signifi - (P  >  0.01) between the soils under all the land use/land cantly (P > 0.01) with land use, but showed no significant cover systems. These results contradict the findings of difference in elevation (Table  6). Also, the interaction Awdenegest et al. (2013) who reported that the CEC con- effects between subjects were not significant. At all ele - centration was low in oxisols under savanna and grazing vations, mean EC values at the surface (0–15  cm) layer land use systems compared to farmland use systems in showed significant differences (P < 0.01) between the soils Southern Ethiopia. under natural forest and those of the other land use/land At mid-altitude, the soils under natural forest land cover systems (Fig. 10). More so, although the EC content cover systems had the highest mean concentration of in soils under farmland were not significantly different CEC (25.8  cmol (+)/kg soil) followed by those under E. (P  >  0.01) from those for soils under the other land use saligna plantations (24.7  cmol (+)/kg soil), while those Tellen and Yerima Environ Syst Res (2018) 7:3 Page 23 of 29 Table 6 Summary of ANOVA for EC, exchangeable cations and CEC in relation to land use and elevation + + 2+ 2+ Source of variations df ECEx. NaEx. KEx. CaEx. Mg CEC MS P MS P MS P MS P MS P MS P Land use (LU) 5 0.016 0.000 0.063 0.681 3.842 0.65 6.734 0.248 2.958 0.091 92.832 0.332 Elevation (E) 2 0.003 0.029 0.077 0.472 13.786 0.001 51.454 0.000 11.39 0.001 105.58 0.271 LU * E 8 0.001 0.209 0.136 0.235 3.182 0.089 26.472 0.000 2.521 0.114 79.766 0.440 Error 80 0.001 0.102 1.768 4.949 1.493 79.446 MS is the mean square, P is the p value, df is degree of freedom systems (except those under natural forest vegetation) at all elevations (high, mid and low), the soils under natural forest had higher EC values (0.18, 0.17 and 0.12  mS/cm, respectively) than those of the other land use/land cover systems (Fig.  25). Therefore, the conversion of forest to cultivated land decreases EC in the study area. These results are in line with the findings of Kizilkaya and Den - giz (2010) who reported that changing forest to cultivated land increased EC values in their area of study due to high application rates of chemical fertilizers. Although EC represents soil soluble salt components, it is believed that the use of basic chemical fertilizer such as ammonium phosphate and urea under farmlands in our study area did not lead to higher EC values above normal (EC  >  0.15 mS/cm will affect plant growth and develop - Fig. 25 Estimated marginal means of electrical conductivity in the ment) when compared to those under natural forest cov- 0–15 cm soil layer across different land use/land cover systems and ers. Therefore, farmers must avoid complete reliance on altitudes chemical inputs but continue to rely more on organic fertigation to keep EC < 0.15 in soils. In this regards, the soils under natural forest at high and mid-altitudes in this study may affect the growth and development of only some EC sensitive plants species since their EC concen- trations are slightly above normal. Effects of  land use change on  exchangeable bases Exchangeable sodium (Na ) (cmol (+)/kg soil) Generally, the results show that mean soil exchangeable Na had no significant differences with land use types (P > 0.01) and across all elevations (Table 6). The concen - tration of exchangeable N a was the smallest component on the exchange complex. In addition, the interaction between subject effects was not significant (P   >  0.01). Although there was no significant differences (P  < 0.01) at the surface (0–15  cm) layer, at high altitude, soils under the protected forest had the highest mean soil exchange- able Na concentrations (1.05 cmol (+)/kg soil) followed Fig. 26 Estimated marginal means of exchangeable Na in the by the soils under farmlands (1.01 cmol (+)/kg soil), while 0–15 cm soil layer across different land use/land cover systems and those under savanna and grazing land use systems had altitudes lower values (0.65 and 0.67, respectively) (Fig. 26). Tellen and Yerima Environ Syst Res (2018) 7:3 Page 24 of 29 This result corroborate the findings of Yimer et  al. (2008) who reported that the concentration of soil exchangeable Na was lower in cropland than in the grazing and native forest. Alem et  al. (2010) also observed higher soil exchangeable N a concentration in soils under E. grandis when compared to those of native forest in Ethiopia. Significantly high concentra - tions of exchangeable Na in the soil in, particularly in proportion to the other cations present, can have an adverse effect on crops and physical conditions of the soil (Yerima and Van Ranst 2005a; Bashour and Sayegh 2007). Although Adetunji (1996) indicated that soils with exchangeable N a of 1  cmol (+)/kg soil should be regarded as potentially sodic, those under native for- est in the study cannot be regarded as sodic soils, since the soil pH was slightly acidic, and there were no exist- Fig. 27 Estimated marginal means of exchangeable K in the ing evidence of soluble salts in the area. In fact, the con- 0–15 cm soil layer across different land use/land cover systems and centration of exchangeable Na in the other land use altitudes systems did not attain 1  cmol (+)/kg soil. The alternate wet and dry seasons and the topographic (drainage) con- layer showed significant differences (P  <  0.01) between ditions may be responsible for the potential sodicity value the soils under natural forest and all the other land use recorded under the protected forest systems in this study. systems except farmland. At mid-altitude, soils under At mid-altitude, soils under the grazing land use had the protected natural forest also had the highest mean the highest mean soil exchangeable N a concentrations soil exchangeable K concentration (1.75  cmol (+)/kg (0.88  cmol (+)/kg soil) followed by the soils under E. soil) followed by the soils under farmlands (1.05  cmol saligna plantations (0.86  cmol (+)/kg soil), while those (+)/kg soil), while those under savanna and grazing land under protected forest and savanna land cover systems use had the lowest concentration (0.25 cmol (+)/kg soil). had the lowest concentrations (0.65  cmol (+)/kg soil). However, at this altitude, mean soil exchangeable K However, at this altitude, mean soil exchangeable N a concentration at the surface (0–15  cm) layer showed no concentrations at the surface (0–15 cm) layer showed no significant difference (P  >  0.01) between the soils under significant difference (P  >  0.01) between the soils under all the land use/land cover systems. all the land use/land cover systems. At low altitude, soils At low altitude, soils under the savanna land use system under the natural forest land use system had the highest also had the highest mean exchangeable K concentra- mean soil exchangeable N a concentrations (0.85  cmol tion (3.10  cmol (+)/kg soil) followed by the soils under (+)/kg soil) while those under E. saligna plantation had farmlands (2.49 cmol (+)/kg soil) while those under nat- the lowest concentration (0.58 cmol (+)/kg soil). This ural forest cover and grazing land use had the lowest con- may be due to the fact that the low soil pH under the centrations (1.90 and 1.83 cmol (+)/kg soil, respectively). Eucalyptus plantation would lead to a decrease in soil At this altitude, mean soil exchangeable K concentra- base saturation, through immobilization of the exchange- tion at the surface (0–15 cm) layer showed no significant able bases, and may result in soil exchangeable bases difference (P > 0.01) between the soils under all the land depletion over time (Aweto and Moleele 2005). use/land cover systems. The observed high concentra - Exchangeable potassium (K , cmol (+)/kg soil) tions of soil exchangeable K under the natural forest The results showed that soil exchangeable K did not land use system can be attributed to a relative pumping significantly vary with land use types (P > 0.01) but varied of potassium from the subsoil to topsoil by vegetation significantly with elevation (P < 0.01) (Table  6). However, (Bohn et  al. 2001). Also, the observed high concentra- the interaction between subject effects was significant tion of soil exchangeable K under the cultivation land (P  >  0.01). At high altitude, soils under the protected use system can be attributed to the observed frequent forest had the highest available potassium concentra- application of household wastes, particularly wood ash, tion (4.00  cmol (+)/kg soil) followed by the soils under as well as burning of farm residues. These results are con - farmlands (2.94  cmol (+)/kg soil), while those under sistent with the findings of Bohn et  al. (2001). Accord - savanna and grazing land use had the lowest concentra- ing to ratings by Landon (1991), soil exchangeable K tions (1.05  cmol (+)/kg soil) (Fig.  27). At this altitude, concentration under the natural forest land use system mean soil available potassium at the surface (0–15  cm) Tellen and Yerima Environ Syst Res (2018) 7:3 Page 25 of 29 and those under all the other land use systems was high the surface (0–15  cm) layer showed no significant dif - across the different elevations except those in grazing ference (P  >  0.01) between the soils under all the land land at mid-altitude which was medium. The medium use/land cover systems. At low altitude, soils under the soil exchangeable K concentrations under grazing land natural savanna land use systems had the highest mean 2+ could be associated with soil degradation and losses due exchangeable Ca concentration (8.50 cmol (+)/kg soil), to leaching as the grazing land was denuded of vegeta- followed by the soils under E. saligna plantation (4.98 tion cover. A critical concentration of 0.12  cmol/kg soil cmol (+)/kg soil), while those under natural forest cover is required for plant growth on oxisols (Yerima and Van had the lowest concentration (2.85  cmol (+)/kg soil). At 2+ Ranst 2005b) and the results indicate that exchangeable this altitude, mean soil exchangeable C a at the surface K concentration is not limiting in the soils of the study (0–15 cm) layer showed significant differences (P < 0.01) area. between the soils under natural forest, savanna, and 2+ Exchangeable calcium (Ca , cmol (+)/kg soil) farmland. 2+ The results showed that soil exchangeable Ca con- According to ratings by Landon (1991), soil exchange- 2+ centrations did not significantly vary with land use able Ca concentrations in the protected forest and type (P  >  0.01) but varied significantly with elevation farmland as well as those under savanna and grazing land (P  <  0.01) (Table  6). However, the interaction between and E. saligna plantation in the high and low altitudes subject effects was significant (P  <  0.01). At high alti - respectively, was medium, while the soil exchangeable 2+ tude, soils under the protected forest had the highest Ca concentrations under all the other land use sys- 2+ mean exchangeable C a concentration (8.25  cmol (+)/ tems across the different altitudes was low. The medium 2+ kg soil) followed by the soils under farmlands (6.00 cmol soil exchangeable Ca in the protected forest, farmland, (+)/kg soil), while those under savanna and grazing land grazing land and E. saligna plantation was probably due use had the lowest (2.00  cmol (+)/kg soil) (Fig.  28). At to the application of household wastes (wood ash in par- 2+ this altitude, mean soil exchangeable C a at the surface ticular) in the fields as well as the burning of floral and 2+ + (0–15 cm) layer showed significant differences (P < 0.01) crop residues since ash is a good source of C a, K , P, 2+ between the soils under natural forest and all the other and Mg (Voundi et  al. 1998) and pumping of bases land use systems except those under farmland. from the subsoil by the vegetation and returning them At mid-altitude, soils under the protected natural for- into the topsoil (Yimer et  al. 2008). On the other hand, 2+ 2+ est also had the highest mean soil exchangeable Ca the low soil exchangeable C a could be as a result of soil concentrations (3.68  cmol (+)/kg soil) followed by the erosion and nutrient losses through leaching as the graz- soils under E. saligna plantation (2.20  cmol (+)/kg soil), ing land was denuded of vegetation cover. A critical con- while those under savanna land cover had the lowest centration of 0.2 cmol/kg soil is required for plant growth concentration (0.80  cmol (+)/kg soil). However, at this in tropical soils (Landon 1991) and the results indicate 2+ 2+ altitude, mean soil exchangeable Ca concentrations at that exchangeable C a is not limiting in the soil of study area. 2+ Exchangeable magnesium (Mg , cmol (+)/kg soil) The results also showed that the concentrations of 2+ soil exchangeable M g did not vary significantly with land use type (P  >  0.01) but significantly differed with altitude (P  <  0.01) (Table  6) with the lowest concentra- tions at mid-altitude (Table  7). More so, the interaction between subject effects was not significant (P > 0.01). At high altitude, soils under protected forest had the highest 2+ mean exchangeable M g concentrations (3.35 cmol (+)/ kg soil) followed by the soils under farmlands (2.69 cmol (+)/kg soil), while those under savanna and grazing land use had the lowest concentrations (0.93 cmol (+)/kg soil) 2+ (Fig.  29). At this altitude, mean soil exchangeable Mg concentration at the surface (0–15 cm) layer showed sig- nificant differences (P  <  0.01) between the soils under natural forest and all the other land use systems, except 2+ those under farmland. Fig. 28 Estimated marginal means of exchangeable Ca in the 0–15 cm soil layer across different land use/land cover systems and At mid-altitude, soils under the protected natural for- 2+ altitudes est also had the highest soil mean exchangeable M g Tellen and Yerima Environ Syst Res (2018) 7:3 Page 26 of 29 Table 7 Mean (± SD) of soil EC, exchangeable cations and CEC in the 0–15 cm soil layer across different land use/land- cover systems and altitudes Soil property Altitude Land use types Virgin forest Virgin savana Farming Park afforesta- Grazing land Eucalyptus ANOVA tion forest Ex. Na (cmol (+)/ High (> 1500 m) 1.05 ± 0.17 0.65 ± 0.06 1.01 ± 0.51 0.67 ± 0.29 0.70 ± 0.21 Ns kg Soil) Mid (900–1500 m) 0.65 ± 0.33 0.65 ± 0.29 0.68 ± 0.23 0.67 ± 0.29 0.88 ± 0.06 0.86 ± 0.44 Ns Low (< 900 m) 0.85 ± 0.52 0.70 ± 0.00 0.68 ± 0.35 0.88 ± 0.21 0.58 ± 0.35 Ns Total 0.85 ± 0.38 0.67 ± 0.16 0.77 ± 0.38 0.67 ± 0.29 0.70 ± 0.29 0.74 ± 0.35 Ex. K (cmol (+)/ High (> 1500 m) 4.00 ± 0.23 1.05 ± 0.64 2.94 ± 1.82 0.74 ± 0.22 1.40 ± 1.40 * kg Soil) Mid (900–1500 m) 1.75 ± 1.57 0.25 ± 0.17 1.05 ± 0.46 0.45 ± 0.24 0.65 ± 0.30 1.04 ± 0.79 Ns Low (< 900 m) 1.90 ± 0.35 3.10 ± 0.00 2.49 ± 3.08 1.83 ± 1.59 2.43 ± 2.02 Ns Total 2.55 ± 1.37 1.47 ± 1.30 2.00 ± 2.04 0.45 ± 0.24 1.18 ± 1.04 1.46 ± 1.37 2+ Ex. Ca (cmol High (> 1500 m) 8.25 ± 0.17 2.00 ± 0.60 6.00 ± 3.24 2.00 ± 0.60 2.93 ± 2.87 * (+)/kg Soil) Mid (900–1500 m) 3.68 ± 2.79 0.80 ± 0.12 1.80 ± 0.79 1.28 ± 0.63 2.18 ± 1.69 2.20 ± 1.59 Ns Low (< 900 m) 2.85 ± 0.29 8.50 ± 0.00 3.63 ± 3.64 4.50 ± 3.54 4.98 ± 4.84 Ns Total 4.93 ± 2.88 3.77 ± 3.55 3.52 ± 3.09 1.28 ± 0.63 2.89 ± 2.39 3.05 ± 2.96 2+ Ex. Mg (cmol High (> 1500 m) 3.35 ± 0.17 0.93 ± 0.55 2.69 ± 1.63 0.93 ± 0.55 1.23 ± 1.20 (+)/kg Soil) Mid (900–1500 m) 1.60 ± 1.44 0.25 ± 0.17 0.98 ± 0.42 0.43 ± 0.21 0.60 ± 0.24 0.94 ± 0.20 Low (< 900 m) 1.70 ± 0.35 2.90 ± 0.00 2.36 ± 2.91 1.73 ± 1.46 2.28 ± 1.86 Total 2.22 ± 1.15 1.36 ± 1.21 1.86 ± 1.89 0.43 ± 0.21 1.08 ± 0.97 1.32 ± 1.23 EC High (> 1500 m) 0.18 ± 0.01 0.07 ± 0.01 0.08 ± 0.02 0.07 ± 0.02 0.08 ± 0.03 * Mid (900–1500 m) 0.17 ± 0.03 0.08 ± 0.01 0.07 ± 0.02 0.06 ± 0.01 0.05 ± 0.00 0.07 ± 0.03 * Low (< 900 m) 0.12 ± 0.06 0.06 ± 0.00 0.07 ± 0.04 0.07 ± 0.05 0.06 ± 0.01 * Total 0.16 ± 0.05 0.07 ± 0.01 0.08 ± 0.03 0.06 ± 0.01 0.06 ± 0.03 0.07 ± 0.02 CEC (cmol (+)/kg High (> 1500 m) 16.3 ± 5.32 23.1 ± 10.9 19.4 ± 12.6 23.1 ± 10.9 17.6 ± 6.78 Ns Soil) Mid (900–1500 m) 25.8 ± 14.2 22.8 ± 9.06 22.8 ± 6.88 19.7 ± 7.38 20.7 ± 1.79 24.7 ± 9.6 Ns Low (< 900 m) 24.0 ± 12.2 34.1 ± 0.00 17.7 ± 8.30 19.6 ± 11.5 22.5 ± 7.44 * Total 22.0 ± 11.1 26.7 ± 9.21 20.4 ± 9.11 19.7 ± 7.38 21.1 ± 8.49 21.4 ± 8.43 Means in the same row followed by the same letters are not significantly different at 1% significance Ns non significance, MC moisture content, BD Bulk density * Significant at P < 0.01 concentrations (1.60 cmol (+)/kg soil) followed by the soils under farmland (0.98 cmol (+)/kg soil), while those under savanna land cover had the lowest concentra- tions (0.25 cmol (+)/kg soil). More so, at this altitude, 2+ mean soil exchangeable M g concentrations at the sur- face (0–15 cm) layer showed no significant difference (P  >  0.01) between the soils under all the land use/land cover systems. At low altitude, soils under the natural savanna land use system had the highest mean exchange- 2+ able Mg concentration (2.90 cmol (+)/kg soil) followed by the soils under farmland (2.36 cmol (+)/kg soil), while those under natural forest cover had the lowest concen- tration (2.85  cmol (+)/kg soil). At this altitude, mean 2+ soil exchangeable Mg at the surface (0–15 cm) layer showed no significant differences (P < 0.01) between the 2+ soils under all the land use/land cover systems. Fig. 29 Estimated marginal means of exchangeable Mg in the Generally, the results for exchangeable bases follow 0–15 cm soil layer across different land use/land cover systems and altitudes a similar trend and hence the simultaneous explanation Tellen and Yerima Environ Syst Res (2018) 7:3 Page 27 of 29 provided above is believed to provide justifications for Table 9 Correlation matrix table for selected soil pH and exchangeable acidity at surface 0–15 cm soil depth these dynamics. According to ratings by Landon (1991), 2+ soil exchangeable M g concentration in all the land use/ pH EA land cover systems was medium, except for those under pH 1 − 0.752** savanna and afforestation in the mid-altitude, which was EA − 0.752** 1 less than the critical level of 0.5 cmol (+)/kg soil. A con- ** Correlation is significant at the 0.01 level; EA is exchangeable acidity centration less than the critical level would require an application of magnesium limestone for management accordingly (Awdenegest et al. 2013). manage the acidity problems, while the observed mod- erate and lower EA values indicates the easiness to also Effects of  LULC change on  soil exchangeable acidity manage the acidity problem of the respective land uses + 3+ (H   +  Al ) The laboratory results showed that some and elevations, within the study area. soils under natural forest cover, farmland and E. saligna According to the Apal Agricultural Laboratory; soil plantations, particularly at high and mid-altitudes, had test interpretation guide (2016), where extractable alu- relatively lower pH values (pH < 5.5), though only mean minum is  >  2, sensitive plants will be affected. It also pH concentrations of soils under farmland are indicated 3+ states that excess soluble/available aluminum (Al ) is in Table  4. These soils were selected and analysed for toxic to plants and can cause a number of problems. The exchangeable acidity (EA) and the results are presented 3+ guide further explains that some issue caused by Al in Table 8. toxicity can include: direct toxicity, primarily seen as It has been well reported that high exchangeable acid- stunted roots; reduction of the availability of phosphorus, ity occurs in very acidic soils, with low pH values (Yer- through the formation of Al-P compounds; reduction of ima and Van Ranst 2005a; Aweto and Moleele 2005). the availability of sulfur, through the formation of Al-S 3+ The hydrolysis of Al ions that constitute part of the compounds; reduction of the availability of other cations clay layers become exchangeable and contribute to 2+ 2+ (Ca and Mg ) through competitive interactions; and the development of soil acidity (Yerima and Van Ranst reduced rhizobium levels on legumes. The high EA under 2005a; Oyedele et  al. (2009). In fact, correlation analysis eucalyptus plantations confirms the low yields observed (Table  9) shows a significantly strong negative relation - for most crops planted around eucalyptus plantations ship (r  =  −  0.752, P  <  0.01) between soil pH and soil and confirms the acidifying nature of eucalyptus leaves exchangeable acidity. Frimpong et al. (2014) stated that at under decomposition. The high EA values in farmland pH below 5.5, aluminum and manganese toxicities might are consistent with the acidification resulting from the occur. application of ammonium fertilizers (Yerima and Van At high altitude, soils under farmland and Eucalyptus Ranst 2005a, b). plantations had high EA values (Ex. Acidity > 2), while at mid-altitude, only those under farmland had a high EA Conclusions value (Table  8). These results indicate that at high alti - This study was aimed at assessing the effects of six land tudes, soils under farmland and Eucalyptus plantations use systems on fifteen soil physicochemical properties in as well as those under farmland at mid-altitude, present the North West region of Cameroon. Ninety soil samples a high potential for aluminum toxicity to plants and may were collected from each land use system at the 0–15 cm have immobilized soil essential nutrients. Aweto and depth for laboratory analysis. The findings suggest that Moleele (2005) reported that soils with higher exchange- LULC change has influenced many soil physicochemical able acidity cause immobilization of soil essential nutri- properties at different topographic altitudes in the North ents including; P, N, Ca, Mg, and K under Eucalyptus spp. West region of Cameroon. The conversion of natural The observed high values of EA indicates a difficulty to forest or savanna to farmland reduced the silt contents, + 3+ Table 8 Means of selected soil exchangeable acidity (H +Al ) in the 0–15 cm soil layer across different land use/land cover systems and altitudes Factor Altitude Land use types Virgin forest Virgin savana Farming Park afforestation Grazing land Eucalyptus forest EA High (> 1500 m) 1.5 – 3.07 – – 3 Mid (900–1500 m) 1.6 – 2.6 – – 1.82 Low (< 900 m) – – – – 0.4 – Tellen and Yerima Environ Syst Res (2018) 7:3 Page 28 of 29 Consent for publication moisture content, organic matter, soil organic carbon, All authors read the manuscript and agree to publication. total nitrogen, available phosphorus, pH, cation exchange capacity, and exchangeable bases, but increased the soil Declaration I, Valentine Asong Tellen, holder of ORCID number 0000-0001-8513-788X bulk density, electrical conductivity, exchangeable acid- hereby declare that this research article is written by the authors whose ity and sand content significantly (P  <  0.05). The results names have been appropriately indicated. revealed that deforestation and subsequent cultivation Ethics approval and consent to participate of soil had negative effects on the measured soil proper - The authors hereby declare that, this manuscript is not published or consid- ties. Therefore, it can be concluded that the conversion ered for publication elsewhere. of natural forest or pasture land to cultivation land sub- Funding jected soil physicochemical properties to degradation Self-funded. thereby sullying soil quality. To reverse soil degradation and promote restoration in the region, emphases should Publisher’s Note be placed on promoting site-specific, sustainable land Springer Nature remains neutral with regard to jurisdictional claims in pub- management practices within the savanna, grazing, agri- lished maps and institutional affiliations. cultural and forest management systems. Received: 29 June 2017 Accepted: 16 January 2018 The scope of this research was limited to only three subdivisions (Santa, Bamenda, and Ndop) under just two divisions (Mezam and Ngoketungia) but gives a repre- sentation of the geomorphic surfaces in the NW region of Cameroon. The research also used only selected soil References Adetunji MT (1996) Field soil tests for NO3, NH4, PO4, K, Ca and Na. Depart- physical and chemical properties as indicators of soil ment of Soil Science and Mechanization, University of Abeokuta, Nigeria. quality under the influence of land use change. Generally, In: Simple Soil, Water and Plant Testing Techniques for Soil Resource soil quality varies greatly with soil type, depth and over a Management. Proceedings of a Training Course Held in Ibadan, Nigeria, 16–27 September 1996. 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Effects of land use change on soil physicochemical properties in selected areas in the North West region of Cameroon

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Environment; Monitoring/Environmental Analysis
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Abstract

Background: Land use changes from natural ecosystems into managed ecosystems may have deleterious effects on soil structure and quality. This study characterise the soils under, and assesses the effects of different land use systems on selected soil physicochemical properties in the North West region of Cameroon. Six land use systems including: natural forest, natural savanna, grazing land, afforested land, farmland and Eucalyptus plantation were identified. Ninety soil samples were collected from each at the 0–15 cm depth. Fifteen soil physicochemical properties were measured. Results: The conversion of natural forest or savanna to farmland reduces the silt contents, moisture content, organic matter, organic carbon, total nitrogen, available phosphorus, pH, cation exchange capacity and exchangeable bases, but increases bulk density, electrical conductivity, exchangeable acidity and sand content significantly (P < 0.05). The results revealed that deforestation and subsequent cultivation of soil had negative effects on the measured soil properties. Conclusions: Land use change has ruined soil quality in the North West region. To reverse soil degradation and promote restoration, emphases should be placed on promoting the use of sustainable land management practices within the savanna, grazing, agricultural and forest management systems. Keywords: Soil quality indicators, Land use change, Soil degradation, Africa, Cameroon changes are indicators of forest resource dynamics within Background a landscape. The dynamics of LULC change associated Land use/land cover (LULC) changes influence the bio - with the anthropogenic activities are occurring rapidly geochemistry, hydrology, and climate of the earth. Eluci- in tropical landscapes. Recent international concerns dating the impact of LULC at the local to regional scales place high attention on monitoring changes in tropical on soil quality status is not direct but rather complex to resources and reporting on those factors (such as agricul- guarantee any generalizations (Hoogsteen et  al. 2015). ture) influencing these changes (such as deforestation), Across sub-Saharan Africa, natural resources remain for consideration of novel scientific and policy inter - central to rural people’s livelihoods (Roe et  al. 2009). ventions (goal #15 of the 2030 Agenda for Sustainable Nonetheless, natural (rainfall and temperature) as well Development). To understand the dynamics of ecologi- as anthropogenic (farming, grazing, burning) forces can cal processes and the impacts related to these changes in exert pressure on these resources, thereby influencing LULC, an assessment of the effects of these changes on spatial and temporal scale changes on a landscape. LULC soil quality is important. According to the United Nations Convention to Com- *Correspondence: tvasong@yahoo.com bat Desertification (UNCCD), 24 billion tons of fertile Department of Development Studies, Environment and Agricultural soils are lost due to erosion every year, while 12 mil- Development Program, Pan African Institute for Development-West Africa lion hectares of land are degraded through drought and (PAID-WA), P.O. Box 133, Buea, South West Region, Cameroon Full list of author information is available at the end of the article © The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Tellen and Yerima Environ Syst Res (2018) 7:3 Page 2 of 29 the encroachment of the desert (this is 23 hectares per sea level. Three study sites were selected following a minute) where 20 million tons of grain could have been stratified random sampling technique. Each stratum rep - grown. Epule et al. (2011) stated that Cameroon’s forests resents a particular topographic zone [the lower altitude are part of the Congo Basin and it is ranked the second (<  900  m); the mid-altitude (900–1500  m) and the high largest tropical rainforest hot spot in the world after the altitude (>  1500  m)] within the North West Region. The Amazon Basin in Latin America largest. FAO (2010a) representative study sites selected include Ndop (lower remarked that Cameroon’s forest contains about 2696 altitude), Nkwen (mid-altitude) and Awing (high altitude) million metric tons of carbon in living biomass. This (Fig. 1). indicates that deforestation is even more intimidating The topography greatly influences the climate with a for the environment. Even so, FAO (2010a, b) reported tropical transition from the rainy humid and continu- that Cameroon forests occupies about 28 million hec- ously warm climate in the South to an extremely unpre- tares (ha) of land and of this number, about 220 thousand dictable (regarding temperature and precipitation) (ha) are lost each year; this is equivalent to about − 1.0% but somewhat dry and hot climate of the North. Abso- of annual forest cover loss. Evidence, though anecdotal, lute annual average precipitation ranges from 1700 to reveals that the population growth in Cameroon and 2824  mm. The high altitudinal areas are cold (<  15  °C) scarcity of arable land has exacerbated food insecurity such as Awing and Santa whereas the low altitude zones and water scarcity. FAO (2009) forecasted that the high are hot (average 27 °C) such as Ndop plain and Ako Sub population density with continued demand for arable Division. There are two distinct seasons: the rainy season land in Africa would amplify deforestation pressure. In (mid-March to mid-October) and the dry season (mid- fact, land degradation is a very serious challenge as it October to mid-March). The vegetation here results from leads to hunger, poverty and is at the root of many con- the prevailing soil conditions, altitude, human activities flicts (FAO 2017). Progress towards meeting the sustain - on the environment and climate. The region lies within able development goal # 15 of the 2030 agenda requires the savannah zone where grasses and shrubs predomi- an understanding of the drivers of soil degradation. nates. The dominant soil type is Oxisol (rich in oxides of It is reported that an ample surface area of African Fe and Al and has a characteristic reddish color) which forests has been lost, with a significant influence result - encourages erosion (pseudo sand and pseudo silt) and ing from small scale agriculture (FAO 2009; Harvey results to gullies on bare surfaces while the valleys are et al. 2004). In fact, Cheek et al. (2000) and Harvey et al. covered with alluvial deposits (Yerima and Van Ranst (2004) projected a 96.5% future loss of the original for- 2005a, b; Yerima 2011). est cover within the Bamenda Highlands, with its climate change implications. The need for sustainable land use- Land use/land cover systems identified in the North West ecosystems conjures the protection and enhancement Region of soil quality through designing efficient site specific Six LULC systems were identified and presented as actions to control erosion and restore soil quality, thereby follows: improving the conditions and productivity of the agro- silvipastoral landscapes in the western highlands region i. Farmland: It is characterized by the cultivation of of Cameroon. The objectives of this study include: (i) to crops such as cabbages, onion, carrot, pumpkins, characterize the soils under the different land use sys - and green pepper. Annual crops such as maize, pota- tems; and (ii) to assess the influence of land use change toes, beans, and pea, are most commonly cultivated on selected soil physicochemical properties in the North (Fig.  2). Subsistence farming characterizes agricul- West region of Cameroon. ture in the study area, and the main cropping system is mixed, although rotation, inter-cropping, mono- Methodology cropping and fallow systems are also common. Description of the study area ii. Natural forest land: It is composed of various indig- This study was conducted in the North West Region enous trees, shrubs, and bushes like Podocarpus of Cameroon which lies between latitudes 5°45″ and falcatus (Zigba) (Fig.  3). The forest is usually found 9°9″  N and longitudes 9°13″ and 11°13″  E. It covers an in protected areas where it is restricted from farm- area of about 17,400  km and is bordered to the North ing or livestock grazing. However, the culture has and West by the Republic of Nigeria, to the South by not allowed replanting (reforestation) and the newly the West and South West Regions and to the East by the germinating seedlings are being destroyed by farm Adamawa Region (Manu et al. 2014). The topography of encroachment and animals browsing and trampling. the Region varies greatly from depressions lower than Due to high deforestation rates, these forests are 400  m above sea level to high mountains, 3000  m above found in patches, often located in valleys and small Tellen and Yerima Environ Syst Res (2018) 7:3 Page 3 of 29 Fig. 1 Topographic map showing the locations where soil samples were collected within the North West Region of Cameroon depressions which often harbor streams and other cies include: pine, Zigba (Podocarpus falcatus), large water bodies. diameter rattans (Laccosperma secundiflorum and iii. Natural savanna: It is composed of short grasses and L. robustum species), mahogany (Swietenia macro- usually located within protected areas (Fig.  4). This phylla King), iroko (Milicia excelsa), Pygeum (Prunus land use system is used for grazing in areas where Africana), mango (Mangifera indica) and other plant no property right exists. It is believed to have been species that have food, fuelwood, medicinal, timber, created due to the shrinkage of the forest cover as a etc., attributes (Yerima 2011). result of deforestation due to human and animal dis- vi. Grazing land: It consists of short grasses (pasture) turbance. and used for cattle grazing and is considered a com- iv. Eucalyptus plantation: It predominantly consists of munal land (Fig.  7). Under such interference, it has two commonly known exotic eucalyptus species in become very difficult to find natural settings in the the region (Eucalyptus salinga and Eucalyptus gran- area (Yerima 2011). dis). These tree stands are indiscriminately planted on water catchments and are gradually replacing Soil sampling and analysis native tree species of the NW region (Fig. 5). The soils were characterized following procedures v. Afforestation area: It is represented by an afforested proposed by (Yerima and Van Ranst 2005a). Soil sam- research unit created in 2010 (6–7  years ago), char- ples were collected from the six main land use systems acterized by fast-growing environmentally friendly described above (Natural forest, natural savanna, farm- tree species for fuel and timber (Fig.  6) to reduce land, afforested land, grazing land and Eucalyptus plan - pressure on the endangered native tree species which tation). Under each land use, soil samples were obtained are at risk of extinction. Some of these plant spe- from a plot, with dimensions of 20 × 20 m (400 m ), at a Tellen and Yerima Environ Syst Res (2018) 7:3 Page 4 of 29 Fig. 2 Collection of soil samples from farmlands on varying geo- Fig. 3 Protected man-made forest at the Yongka Western Highlands morphic surfaces (a); a common tillage practice on farmlands in the Research Garden Park (a); the collection of soil samples from a natu- North West Region (b) rally protected forest adjacent to Lake Awing (b) constant depth of 0–15 cm, following a “Z-layout” design. soils were analysed at the Soil Science Laboratory at the Soil samples were taken from the four corners and center University of Dschang, following standard procedures of each layout. Approximately 1  kg of composite sample and methods as described below: was collected from each location and placed into plastic bags. They were then transported, air-dried at room tem - Physical properties perature, crushed, homogenized, and passed through a Moisture content (MC) was calculated using the gravi- 2  mm sieve before laboratory analysis. A total of 90 soil metric method where soil samples were placed into samples (six land use types x five replicates per sample ceramic crucibles and weighed to get the fresh weight plots x one soil depth class: 0–15  cm  ×  three altitudi- and then oven-dried at 105  °C to constant weight for nal zones) were collected within the study area, from about 24  h and the dry weight recorded. These values June to July 2015, for analysis. Undisturbed soil samples were then used to calculate the moisture contents of the were taken with a core sampler that was 7.5  cm long soils using the formula: and 6.4  cm in diameter for bulk density determination. 100 (fw − dw) Soil quality indicators comprising of the three standard MC (%) = dw groupings including: physical (moisture content, bulk density); chemical (pH, total nitrogen, available phospho- where MC soil moisture content (%), fw fresh weight (g) rus, exchangeable bases, cation exchange capacity, C/N of soil sample, dw dry weight (g) of soil sample. ratio, electrical conductivity) and biological (organic mat- Bulk density was measured following the core method ter content) proposed by Yerima and Van Ranst (2005a), described by Yerima and Van Ranst (2005a, b), where for soils in the tropics, were selected for analysis. The samples contained in the core rings of known weight, Tellen and Yerima Environ Syst Res (2018) 7:3 Page 5 of 29 Soil bulk density was then determined using the follow- ing formula: BD = M/V, where BD bulk density, M mass of oven dry soil (g) and V volume of core (cm ). Soil textural fractions (sand, silt, and clay) were ana- lyzed following the Bouyoucos hydrometer method, where 15  g of 2  mm air-dried soil was weighed into 500  ml beakers and subjected to treatments for remov- ing organic matter using H O , followed by dispers- 2 2 ing the soils with sodium hexametaphosphate (Pauwels et  al. 1992). The resulting compositions were placed on a mechanical shaker and allowed to shake for 3  h. Sus- pensions were then transferred into sedimentation meas- uring cylinders and brought to the 1000  ml mark using distilled deionized water. The mixtures were well stirred using a mechanical rotator to bring the particles into sus- pension. A hydrometer was then used to obtain readings after 40 s (first reading, R1) and 2 h, (second reading, R2) respectively. Calculations were done using the following Fig. 4 Natural savanna grassland located near a palm plantation equations: at Nkwen, Bamenda (a); the collection of soil samples from natural savanna land at the Yongka Park (b) R1 % (Silt + Clay) = × 100 (A) The first reading (R1) gave the silt + Clay content R2 − R1 But % Clay = × 100 (B) Therefore, % Silt  =  A  −  B while % Sand  =  100  −  % (Silt + Clay). After getting the percentage sand, silt and clay, the soil textural triangle was used to classify the soil texture. Chemical analysis Moisture correction factor was calculated using the fol- lowing formula: 100 + MC (%) mcf = where mcf moisture correction factor and MC soil mois- Fig. 5 Eucalyptus salinga plantation at Awing ture content (%). Soil pH was measured both in water and KCl (a 1:2.5 soil: H O/KCl ratio) using a glass electrode Thermo- height and diameter were weighed and the fresh weights Russel pH meter, calibrated using buffer solutions of pH recorded, then oven dried at 105 °C for 24 h, after which 7 and 4 for H O and KCl, respectively. Soil total nitro- the dry weights were also recorded. The volume of the gen (TN) was determined using the Kjeldahl distillation core was determined using the following formula: method (Pauwels et al. 1992) where 1 g each of air-dried soil samples were placed into 500 ml Kjeldahl flasks, fol - 2 3 V = π r h cm , lowed by the addition of 5 ml of distilled deionized water. A scoop of digestion accelerator mixture (sulphuric–sali- where V  =  volume of core (cm ); π  =  3.14; cylic acid mixture) was then added to each flask. Five mil - r = radius = diameter/2 (cm); and h = height (cm). liliter of concentrated H SO was added and the mixture 2 4 Tellen and Yerima Environ Syst Res (2018) 7:3 Page 6 of 29 Fig. 6 Nine year old Eucalyptus saligna tree stand (a); 8 years old Podocarpus (Podocarpus falcatus) tree stand (b); collection of soil samples under a Jackfruit tree stand (c); collection of soil samples under a mixed fruit tree stand (Prunus domestica, Mangifera indica) at the Yongka Highland Research Garden Park (d) was allowed to digest for 1 h in a fume cupboard by gen-0.03 N NH F were used to extract available phosphorus tle heating until the vigorous effervescence subsided to from the soil samples. Phosphorus was determined color- ensure that the digest was free of charred organic matter. imetrically using the ammonium molybdate blue method. The digest was then allowed to cool followed by addition In this process, 2 g of < 2 mm air-dried soil samples were of 20 ml of distilled water. After ensuring settlement, the weighed into clean dried test tubes. Fourteen ml of the supernatant solutions were decanted into 100  ml volu- extracting solution was added and vigorously shaken for metric flasks. The process was repeated and 5 ml of 40% 30  s, using an electrical shaker and immediately filtered NaOH and 100 ml of distilled water were added. The dis - into other previously prepared test tubes carrying funnels tillate was collected and mixed with 5 ml of the boric acid and Whatman # 42 filter papers. For colour development, (H BO ) solution-indicator mixture. The distillate was 5 ml of the extract and standards were pipetted into a set 3 3 titrated with 0.01  M H SO from green to pinkish end- of test tubes. Then, 5 ml of colour development reagents 2 4 point and the titer value recorded. The soil TN was calcu - (Ascorbic acid), and mixed reagent (Ammonium molyb- lated using the formula: date, Potassium Antimony tartrate and sulphuric acid) were added to each test tube. The samples were allowed 2.8 to stand for 15  min for complete color development. Kjeldahl N (%) = (T − B) × M × Absorbance was then measured using a colorimeter, set where T ml of standard acid with sample titration, B ml of at a wavelength of 882 nm. 2+ 2+ + standard acid with blank titration, M molarity of sulphu- Exchangeable bases (Ca, Mg, K , and Na) were ric acid, S weight of soil sample (g), and 2.8 a constant. extracted using 50  ml of ammonium acetate (1.0  M Available phosphorous (Av.P) was determined follow- NH OAc) solution buffered at pH 7. Potassium (K ) and ing Bray-II method where solutions of 0.1  N HCl and sodium (Na ) in the extract were determined using the Tellen and Yerima Environ Syst Res (2018) 7:3 Page 7 of 29 sample was distilled and the distillate in the conical flasks titrated with 0.01 M H SO from a burette. The CEC was 2 4 then calculated using the following formula: EC 100g soil = (V − Vo) × 1.6 where V the volume of sulfuric acid added to the sample, Vo the volume of sulfuric acid added to the blank, and 16 a constant. Electrical conductivity (EC) was determined following standard procedures proposed by Pauwels et  al. (1992) where a 1:5 soil-solution ratio (10  g of  <  2  mm soil and 50  ml distilled ionized water) was agitated for an hour and the readings from an EC meter, calibrated with 0.01 N KCl, recorded. + 3+ Exchangeable acidity (EA) (H  + Al ) was determined for samples with pH < 5.5. In the procedure, 1 N KCl was added to the flasks containing 1  g of  <  2  mm soil sam - 3+ + ple for displacement of the Al  + H ions. EA was then determined by titration of extracts with 0.02  N NaOH for the neutralization of the acidic ions in the extract using three drops of phenolphthalein as an indicator. The exchangeable acidity was then calculated using the fol- lowing formula: −1 EA meq 100g = 40 × t × (Vx − Vo) + 3+ where EA the exchangeable acidity (H   +  Al ) −1 (meq 100 g ), t the exact molarity of NaOH used, Vx the volume of NaOH added to the sample, Vo the volume of Fig. 7 Collection of soil samples from grazing land at Ntambang (a) NaOH added to the blank. and Santa (b) C/N ratio was obtained by taking the ratio of S percent carbon to nitrogen in each sample as follows: SOC (%) 2+ C/N = flame photometer while magnesium (Mg ) and calcium TN (%) 2+ (Ca ) in the extract were determined by complexomet- where C/N the ratio of carbon to nitrogen, SOC the con- ric titration. centration to carbon (%) in the soil sample, TN the con- Cation exchange capacity (CEC) was determined fol- centration of total nitrogen (%) in the soil sample. lowing the extraction method were soil samples were also Soil organic carbon (SOC) was determined following saturated with ammonium acetate buffered at pH 7 to the Walkley and Black wet oxidation method (Walkley displace the exchangeable bases as explained in the case and Black 1934) where 5 g each, of the soil samples, were of the determination of exchangeable bases. However, for first placed into a wide-mouth Erlenmeyer flask, followed CEC determination, the column of each sample was then by the addition of 10  ml of 1  N Potassium dichromate thoroughly washed with 95% alcohol to discard excess (K Cr O ) into each flask, in a fume cupboard. Twenty 2 2 7 ammonium acetate that saturated the complex. This was milliliter of concentrated sulphuric acid (H SO ) was 2 4 verified using Nessler’s reagent. Sixty milliliter of KCl was then added to each flask and the solution mixture was then added to each tube to allow potassium to replace allowed to stand for at least 30  min. One hundred and ammonium ions on the exchange complexes. The fil - + fifty milliliter of distilled water was then added to each trate containing the NH4 ions was collected into 100 ml flask followed by one drop of the indicator Barium diphe - volumetric flasks and brought up to 100 ml mark by the nylamine sulfate. The solution was then titrated with addition of KCl. Twenty-five milliliter of each sample ferrous sulfate solution while stirring the mixture to the were transferred into distiller’s tubes and NaOH added end-point (when the brown colour changes sharply to followed by 2–3 drops of the end-point indicator, phenol- green). The amount of ferrous sulfate required for each phthalein. Forty ml of boric acid were placed into conical sample for complete combustion was read and recorded. flasks and distilled water added to the 100 ml level. Each Tellen and Yerima Environ Syst Res (2018) 7:3 Page 8 of 29 The difference between the amounts of FeSO added for formation of pedogenic horizons. Hence, a characteristic the samples compared to that added to the blank titration lack of genetic horizons (Fig. 8). determines the amount of combusted carbon. A correc- Yerima (2011) stated that these soils differ in such tion factor of 0.39 was used to account for the incomplete characteristics as texture, effective depth, gravel content, combustion of organic carbon. The percent carbon con - compactness and water infiltration rates. At Ndop, (low tent of the soil samples was then calculated using the fol- altitude), the soils were observed to be rich in alluvial lowing formula proposed by Van Reewijk (2002): deposits and this is corroborated by the fact that Ndop plain is an intermontane basin in the Bamenda High- V 1 − V 2 lands. The soil types observed here include; Inceptisols, % OC = M × × 0.39 × mcf Entisols, and Oxisols. It was suggested that due to these where M the molarity of ferrous sulfate solution (from variations in soil types across elevation, important differ - blank titration), V1 the ml of ferrous sulfate solution ences in physical, chemical and biological characteristics required for blank, V2 the ml of ferrous sulfate solution exist at regional scale. required for sample, S the weight of the air-dry sample in gram, mcf the moisture correction factor, while 0.39 a Effect of LULC change on soil physical properties constant. Table 1 presents the means (± SD) while Table 2 presents a summary of ANOVA for soil MC, BD and particle size Statistical analysis distribution in the soil surface layer (0–15 cm) across dif- The data were analyzed using descriptive and multivari - ferent LULC systems and altitudes. The results for the ate statistics using SPSS version 21.0 for windows. Data individual soil quality attributes include: distributions were checked for normality and then lo g transformed when they were skewed. Pearson’s cor- Soil moisture content (MC) The results also show that relation was used to analyse the relationship between soil moisture content significantly varied with land use selected soil physical and chemical properties. The means types (P  <  0.01) and with elevation (P  <  0.01) (i.e. MC and standard deviations of the selected parameters were increases with increase in altitude (Table 1). Generally, at compared to show their distribution across different land all the elevations, the soils under Eucalyptus saligna plan- use/land cover systems and altitudes in the region. Anal- tation had the highest moisture contents compared to the ysis of variance ratio (ANOVA) was used to test for sig- other land uses/land cover systems except for those under nificant differences between the means, with treatments natural forest land cover systems at the high and low alti- (land use) and group (elevation) set as the independent tudes (Fig. 9). These results corroborate with the findings variables, to determine which parameters varied signifi - of Getachew et al. (2012). cantly with each treatment (Brejda et al. 2000a, b). Soil moisture content (%) at the surface (0–15  cm) showed significant differences (P < 0.01) between the soils Results and discussion of the different land uses/land cover for all the elevation Descriptions and characteristics of soils in the study area (Table 2). At high altitude, the mean soil MC (%) differed In Awing and Santa (high altitude), the soils were pre- significantly (P  <  0.01) between farm and natural forest sumably Inceptisols because they were young soils with only. The study show empty patches with predominantly some colour changes and have rocks at very shallow fern plants under Eucalyptus plantations compared to a depths. In Bamenda (mid-altitude) and at the Yongka dense, continuous layer of undergrowth including Cyno- Park in particular, the soil type varied and was found to don dactylon, Podocarpus sp. found under native forest include: Oxisols, those that possessed loamy and clayey stands (Fig.  10). At mid-altitude, the mean soil MC (%) texture, slightly acidic, contain little or no weatherable under natural savanna forest cover differed significantly minerals, traces of water dispersible clay and extreme (P  <  0.01) from those under E. saligna plantation. Also, weathering of most minerals other than quartz to kao- the mean soil MC (%) under the E. saligna plantation dif- linite and free iron oxides, and have low CEC (< 16 cmol fered significantly (P < 0.01) from those under the affor - (+)/kg); Inceptisols, those that have rocks at vey shal- estation plantations in the Yongka Western Highlands low depth, and were young soils; and Entisols, those that Research Garden Park and grazing land use systems. At lack pedogenic horizons and occur on slopes. The Oxi - low altitude, the mean soil MC (%) under Natural Forest sols presented their characteristic reddish-brown colour, cover differed significantly (P < 0.01) from those under all indicating the presence of oxides of Fe, while Entisols the other land use systems except E. saligna plantation. were observed at the foot of the slope, in areas with fre- Also, the mean soil MC (%) under natural savanna forest quent water saturation and on shoulder slopes where the cover and grazing land use differed significantly (P < 0.01) rate of erosion was presumably higher than the rate of from those under natural forest. Generally, the lower MC Tellen and Yerima Environ Syst Res (2018) 7:3 Page 9 of 29 Fig. 8 Soil profiles showing; Entisol with thin A horizon (a); inceptisol (b); inceptisol with thick A horizon (c) and Entisol exposing stony horizons that constraint plant growth (d) in the North West Region (Source: Yerima (2011)) (%) in soils under E. saligna plantation compared to those Although House (1992) stated that the presence or under natural forest may be due to the observed sparse or absence of understorey is a factor of the density of the absence of undergrowth (Fig. 11). stand and of the rainfall regime, Zerga (2015) reported a In agreement with Aweto and Moleele (2005), the similar finding in Ethiopia and indicated that the domi - sparse or absence of undergrowth and the light canopy nant leaf litterfall under Eucalyptus stands prohibits the of Eucalyptus trees in plantations can lead to higher growth of other plants due to its allelopathic effect. The rate of soil water evaporation, whereas the dense under- latter explained that chemicals from the leaves of Euca- growth in the native forest could lower soil temperature lyptus trees reduce the soil nutrients that are necessary and reduce evaporation to enhance soil water infiltration. for undergrowths, hence, enhancing soil degradation These results also agree with the findings of Cao et  al. through erosion, nutrient and water depletion. It was also (2010) who reported low soil moisture contents, ranging observed in this study that the establishment of euca- from 20.2 to 30.5% in the topsoil (0‒10 cm) under Euca- lyptus plantation not only suppresses undergrowths but lyptus spp. plantations, aged from 3 to 13 years in China. also affects the performance of cultivated crops adjacent The sparse or absence of undergrowth is an indication to the plantation stands, probably due to this allelopathic of reduced biodiversity under Eucalyptus plantations. effects. Tellen and Yerima Environ Syst Res (2018) 7:3 Page 10 of 29 Table 1 Mean (± SD) of soil MC, BD and particle size distribution in the soil layer of 0–15 cm across different land use/ land cover systems and altitudes Soil property Altitude Land use types Virgin forest Virgin savana Farming Park afforesta- Grazing land Eucalyptus P value tion forest a ab b ab ab MC (%) High (> 1500 m) 8.69 ± 0.34 6.96 ± 0.84 5.06 ± 1.33 – 6.96 ± 0.84 6.97 ± 3.31 * ab ac ac ad ce b Mid (900–1500 m) 5.55 ± 1.16 2.78 ± 0.12 3.90 ± 0.85 3.49 ± 0.686 2.42 ± 1.42 5.83 ± 2.02 * a b b b ab Low (< 900 m) 6.98 ± .1.984 2.31 ± 0.83 3.03 ± 1.56 – 2.30 ± 0.83 4.77 ± 0.68 * Total 7.07 ± .1.81 4.01 ± 2.26 3.99 ± 1.41 3.49 ± 0.69 3.90 ± .2.438 5.86 ± 2.51 * 3 a b b b b BD (g/cm ) High (> 1500 m) 0.51 ± 0.03 0.84 ± 0.09 0.89 ± 0.09 – 0.84 ± .009 0.756 ± .151 * a b c bd c bd Mid (900–1500 m) 0.57 ± 0.11 0.87 ± 0.10 1.11 ± 0.24 0.94 ± 0.09 1.19 ± 0.17 0.80 ± .072 * a b c b d Low (< 900 m) 0.79 ± 0.11 1.45 ± 0.00 1.08 ± 0.20 – 1.39 ± 0.08 0.80 ± 0.07 * Total 0.63 ± 0.15 1.05 ± 0.30 1.04 ± 0.21 0.94 ± 0.09 1.14 ± 0.26 0.78 ± 0.11 ab ab b ab ac Sand (%) High (> 1500 m) 28.50 ± 0.58 37.50 ± 1.95 28.38 ± 7.15 – 37.50 ± 1.91 37.0 ± 5.35 * a a a a a a Mid (900–1500 m) 36.50 ± 5.80 34.00 ± 6.93 34.50 ± 4.98 36.92 ± 4.46 32.00 ± 4.97 35.4 ± 9.99 NS ab ab b ab ac Low (< 900 m) 38.00 ± 0.00 37.00 ± 0.00 41.88 ± 5.69 – 31.50 ± 8.43 35.2 ± 6.702 * Total 34.33 ± 5.31 36.17 ± 4.09 34.86 ± 7.67 36.97 ± 4.46 33.67 ± 5.93 36.0 ± 7.427 ab ab b ab ac Silt (%) High (> 1500 m) 57.00 ± 0.00 48.00 ± 2.00 56.13 ± 6.49 – 48.00 ± 2.00 48.0 ± 5.657 * a a a a a a Mid (900–1500 m) 47.00 ± 5.89 52.00 ± 5.77 48.00 ± 5.94 45.50 ± 4.10 53.00 ± 6.93 49.0 ± 10.7 NS ab ab b ab ac Low (< 900 m) 43.00 ± 0.00 47.00 ± 0.00 42.00 ± 5.76 – 51.50 ± 9.15 52.00 ± 5.29 * Total 49.00 ± 6.88 49.00 ± 3.91 48.61 ± 7.98 45.50 ± 4.10 50.83 ± 6.46 49.20 ± 7.81 a a a a a Clay (%) High (> 1500 m) 14.50 ± 0.58 14.50 ± 1.00 15.12 ± 0.99 – 14.50 ± 1.00 14.63 ± 2.77 NS a a a a a a Mid (900–1500 m) 16.25 ± 2.87 13.50 ± 1.73 17.17 ± 2.69 17.25 ± 3.77 14.75 ± 2.75 15.25 ± 2.96 NS a ab ab ab b Low (< 900 m) 18.50 ± 0.58 16.00 ± 0.00 16.00 ± 1.69 – 16.75 ± 2.22 12.7 ± 3.50 * Total 16.42 ± 2.31 14.67 ± 0.50 16.25 ± 2.17 17.25 ± 3.77 15.33 ± 2.18 14.50 ± 2.98 Means in the same row followed by the same letters (a, b or c) are not significantly different at 1% significance NS non significance, MC moisture content, BD bulk density * Significant at P < 0.01 Table 2 Summary of ANOVA for BD, MC, and particle size distribution in relation to land use and elevation Source of variations df BD MC Clay Silt Sand MS P MS P MS P MS P MS P Land use (LU) 5 0.485 0.000 23.725 0.000 17.158 0.023 37.487 0.391 20.638 0.689 Elevation (E) 2 0.653 0.000 71.025 0.000 10.801 0.181 111.44 0.049 55.171 0.197 LU * E 8 0.113 0.000 4.987 0.034 9.176 0.16 124.66 0.002 102.48 0.005 Error 80 0.019 2.246 6.177 35.486 33.329 MS is the mean square, P is the p value, df is degree of freedom Soil bulk density The results also showed that soil bulk and further depicts the altitudinal variations. In terms density significantly varied with land use types (P < 0.01) of absolute values however, the results for this research and across elevation (P < 0.01) with significant interactions showed that soils under farmland had the highest bulk between subject effects (land use and elevation) (P < 0.01) density (0.894 and 1.450  g/cm ), while those under the (Table 2). Generally, at all altitudes, the soil under natural natural forest had the lowest bulk density, (0.517 and 3 3 forest had the lowest bulk density (g/cm ) compared to 0.790 g/cm ) in the top 0–15 cm soil layer at high and low the other land use s/land cover systems, followed by the altitudes respectively. At mid-altitude, soils under graz- soil under E. saligna plantation, while soil under farmland ing land use system had the highest bulk density (1.185 g/ and grazing land had a higher bulk density (Fig. 10). These cm ) while those under the natural forest land cover sys- results corroborate the findings of Getachew et al. (2012) tem had the lowest bulk density (0.570 g/cm ) in the top Tellen and Yerima Environ Syst Res (2018) 7:3 Page 11 of 29 this altitude, bulk density (g/cm ) showed no significant difference between soils under natural savanna and those under farmland, grazing land, and E. saligna planta- tion, respectively. Also, bulk density (g/cm ) showed no significant difference (P  >  0.01) between the soils under farmland and E. saligna plantations. At mid-altitude, bulk density (g/cm ) also showed significant differences (P  <  0.01) between the soils under natural forest and all the other land use/land cover systems except natu- ral savanna and E. saligna plantations. At this altitude, bulk density (g/cm ) showed no significant difference (P  >  0.01) between soils under natural savanna and all other LULC systems except grazing land. At low alti- tude, bulk density (g/cm ) differed significantly (P < 0.01) between the soils under natural forest and all the other Fig. 9 Estimated marginal means of soil moisture content (%) in the land use/land cover systems except those under the E. soil layer of 0–15 cm across different land use/land cover systems and saligna plantation. However, at this altitude, bulk density altitudes (g/cm ) showed no significant difference between soils under natural savanna and those under grazing land. Soil bulk density represents a measure of soil compac- tion and health. Kakaire et al. (2015) stated that a higher soil bulk density means that less amount of water is held in the soil at field capacity, while a lower soil bulk den - sity means soils are less compacted and are able to retain more water. These results corroborate the findings of Ravina (2012) who reported a higher soil bulk density of 1.24  g/cm under Eucalyptus spp. plantation compared to 0.66  g/cm under a native forest in a Brazilian soil (0–15  cm). In addition, Kolay (2000) indicated that bulk density of productive natural soils generally ranges from 1.1 to 1.5 g/cm . Since the soil bulk densities found in all the land uses were lower and within this range, it can be concluded that the soil productivity in the area is good. Furthermore, since the soil bulk densities found in the Eucalyptus plantation, grazing land, and farmland were Fig. 10 Estimated marginal means of bulk density (g/cm ) in the of higher than those under native forest, it can be concluded 0–15 cm soil layer across different land use/land cover systems and that the conversion of forest to Eucalyptus plantations, altitudes farmland and grazing land increases soil bulk densities probably due to increased soil compaction. The find - ings from the study confirm those of Aweto and Moleele 0–15 cm soil layer. It can be suggested that deforestation (2005), who concluded that Eucalyptus spp. plantations and subsequent tillage practices resulted in soil compac- increased soil bulk density more than the native forest in tion, low infiltration and hence increased in bulk density Botswana. for surface soil in North West Region of Cameroon. Simi- lar finding has been reported in other areas around the Particle size distribution Although not significant, the world (Getachew et al. 2012; Javad et al. 2014). results show that particle size distribution varied with Nonetheless, bulk density (g/cm ) showed a significant LULC systems across the different altitudes. However, the difference (P  <  0.01) at all altitudes, between the soils of interactions between subject effects were only significant the different land uses/land cover system for the surface (P < 0.01) for sand and silt contents (Table 2). 0–15  cm soil layer (Table  1). At high altitude, bulk den- sity (g/cm ) differed significantly (P  <  0.01) between the Sand content soils under natural forest and all the other land use/land At high altitude, the soils under both natural savanna and cover systems except E. saligna plantations. However, at grazing land use systems had the highest percentage of Tellen and Yerima Environ Syst Res (2018) 7:3 Page 12 of 29 Fig. 11 Eucalyptus plantation showing sparse undergrowth (a); absence of undergrowth with light canopy (b); native forest showing dense under- growth (c); dark forest canopy with mushroom growing on plant remains (d) sand content (37.5%), while those under natural forest and cropland had the lowest (28.5 and 28.4%, respec- tively) (Fig.  12). This is probably due to the fact that there was no existing land uses where savanna vegeta- tion was protected against disturbance either by burn- ing or grazing in the area. The lower sand content under farmland may be attributed to tillage practices and dif- ferential segregation by erosion on inceptisols. However, at this altitude, mean percentage sand content at the sur- face (0–15  cm) layer showed no significant difference (P  >  0.01) between the soils under all the land use/land cover systems. At mid-altitude, the soils under afforesta - tion land use systems in the Yongka Park had the high- est percentage of sand content (36.9%) while those under grazing land had the lowest (32%). Although the graz- Fig. 12 Estimated marginal means of sand (%) in the 0–15 cm soil ing land had low sand proportions at this altitude, mean layer across different land use/land cover systems and altitudes percentage sand content at the surface (0–15  cm) layer showed no significant difference (P  >  0.01) between the Tellen and Yerima Environ Syst Res (2018) 7:3 Page 13 of 29 soils under all the land use/land cover systems. This can indicator for evaluating soil degradation under different be due to the fact that the soils are oxisols, originating land use systems. from a granitic parent material, characterized by colloidal fractions and dominated by low activity clays and sesqui- Silt content oxides (Yerima and Van Ranst 2005b). At high altitude, the soils under the natural forest land The soils under afforestation land use system in the cover system had the highest percentage of silt content park are varied, which is probably a representation of the (57%), while those under farmland was intermediate different stages of soil development. The park area was (56%) (Fig. 14). Those under the natural savanna, grazing formerly a grazing land, with an unstable geomorphic land and E. saligna plantation had the lowest percentages surface, which resulted in soil erosion and exposure. The and of equal values (48%). However, at this altitude, mean gullies observed under the afforestation stand with Arto - percentage silt content at the surface (0–15  cm) layer carpus heterophyllus (Jackfruit) is associated with the showed no significant difference (P  >  0.01) between the concentration of runoff water from the road (Fig. 13). soils under all the LULC systems. At low altitude, the soils under farmland had the It was noticed that the area under natural savanna highest percentage of sand content (41.9%) while those forest cover at high altitude was also used for grazing. under grazing land use systems had the lowest (31.5%). The frequent burning of grass during the dry season by Again, at this altitude, mean percentage sand content at the surface (0–15  cm) layer showed no significant dif - ference (P  >  0.01) between the soils under all the land use/land cover systems. There was no existing land uses where natural forest cover and savanna vegetation was protected against disturbance either by burning or graz- ing in this area. Therefore there were high similarities with nonsignificant differences in soil properties under the different land uses in this area. Generally, the results showed that sand content increased when converting natural forest to cropland, and this is most likely resulting from the preferential removal of clay and silt and residual accumulation of sand in soil surface resulting from pref- erential segregation and evacuation of the smaller silt and clay particles, by accelerated water erosion. These results are in agreement with the findings of Javad et  al. (2014) who attesting to the results of Ayele et al. (2013) reported Fig. 14 Estimated marginal means of silt (%) in the 0–15 cm soil layer that sand content is a physical parameter affected by across different land use/land cover systems and altitudes soil erosion and, hence, can be measured and used as an Fig. 13 Artocarpus heterophyllus afforested stand (a); gully erosion under the Artocarpus heterophyllus stand (b) Tellen and Yerima Environ Syst Res (2018) 7:3 Page 14 of 29 cattle herdsmen and trampling effects due to overgraz - ing is suggested to have influence soil structure as burn - ing destroys and removes soil organic matter, thereby loosening of soil particles and encouraging water ero- sion on gentle slopes. In addition, the E. saligna planta- tion here was located on steep slopes, with abundant leaf litter and no vegetation understory. It can be suggested that the silt content under natural savanna, grazing land and E. saligna plantation were lower due to accelerated water erosion. The lack of ground cover and understory may have contributed to initiating erosion which selec- tively washes away clay and silt. At mid-altitude, the soils under grazing land use systems had the highest percent- age of silt content (53%) while those under the afforesta - tion land use projects in the Yongka Park had the lowest Fig. 15 Estimated marginal means of clay (%) in the 0–15 cm soil percentage (47%). At this altitude, mean percentage silt layer across different land use/land cover systems and altitudes content at the surface (0–15  cm) layer showed no sig- nificant difference (P  >  0.01) between the soils under all the land use/land cover systems. The soils under the natural savanna land cover had the lowest percentage afforestation stand were located on the shoulder of the (13.5%). At this altitude, mean percentage clay content at slope and signs of severe erosion (rills and gullies) were the surface (0–15 cm) layer showed no significant differ - observed, compared to those of grazing land. Geologi- ence (P > 0.01) between the soils under all the land use/ cally, on a midslope, the rate of soil erosion is increased land cover systems. At low altitude, the soils under the and the topsoil layer is greatly reduced. At low altitude, natural forest land cover system had the highest percent- the soils under the E. saligna plantation had the highest age of clay content (18.5%) while those under E. saligna percentage of silt content (52%) while those under farm- plantation had the lowest (12.8%). At this altitude, mean land use systems had the lowest (42%). At this altitude, percentage clay content at the surface (0–15  cm) layer mean percentage silt content at the surface (0–15  cm) showed no significant difference (P  >  0.01) between the layer showed no significant difference (P > 0.01) between soils under all the land use/land cover systems. However, the soils under all the land use/land cover systems. Here the percentage clay content was relatively lower than the soils under the E. saligna plantation were located on those of sand and silt in all the land use/land cover sys- the toe slope (flat surface) and signs of severe deposition tems across the different altitudes. When fine particles (siltation, floods and stagnant water bodies) were gener - of soils are high, EC may increase. However, increased ally observed in the area after heavy rainfall. Geologically, EC in soils is predominantly due to the presence of solu- on the toe slope, the rate of soil erosion is minimal and ble salts (Yerima and Van Ranst 2005a), but which is not the topsoil layer is mostly comprised of mineral deposits found in the study area, and this may cause instability of transported principally by water (erosive agent) from top soil structure. and shoulder slopes. However, soils under farmland use systems are prone to erosion comparatively. Soil texture Generally, the results show that the soil tex- ture in the study area ranged from loam to silt loam, which Clay content is very good for agriculture. Specifically, the result shows The result shows that at high altitude, the soils under that on one hand, the soil texture under natural vegeta- farmland use system had the highest percentage of clay tion cover and farmland use systems in the NW region content (15%), while those under E. saligna plantation changed from silt loam to loam, as elevation decreases was intermediate (14.6%) (Fig. 15). Those under the natu - (Table 3). On the other hand, the soil texture under graz- ral savanna, natural forest, and grazing land had the low- ing land use system and E. saligna plantation changed est percentages and of equal values (14%). At this altitude, from loam to silty loam as elevation decreases. This is sug - mean percentage clay content at the surface (0–15  cm) gested to be due to pedogenic processes including degra- layer showed no significant difference (P > 0.01) between dation (surficial erosion) and aggradation (cumulization) the soils under all the land use/land cover systems. (Yerima and Van Ranst 2005a). At mid-altitude, the soils under the afforestation land Ideally, the conversion of forest into cropland is known use projects in the Yongcak Park had the highest per- to deteriorate soil physical properties and making the centage of clay content (17.3%) while those under the Tellen and Yerima Environ Syst Res (2018) 7:3 Page 15 of 29 Table 3 Soil texture in the 0–15 cm soil layer across different land use/land cover systems and altitudes Soil property Altitude Land use types Virgin forest Virgin savana Farming Park afforestation Grazing land Eucalyptus forest Texture High (> 1500 m) Silt loam Loam Silt loam – Loam Loam Mid (900–1500 m) Loam Silt loam Loam Loam Silt loam Loam Low (< 900 m) Loam Loam Loam – Silt loam Silt loam land more susceptible to erosion since soil structure Effects of land use change on soil chemical properties (macroaggregates) is disturbed. Soil erosion can mod- Generally, the chemical properties of soils show vari- ify soil properties by reducing soil depth, changing soil ations under the different land uses across the differ - texture, and by the loss of nutrients and organic matter ent altitudinal zones of the study area. Table  4 presents (Lobe et al. 2001). the mean (±  SD) while Table  5 present the summary of Table 4 Mean (± SD) of soil pH, SOC, TN, and Av.P in the 0–15 cm soil layer across different land use/land cover systems and altitudes Soil property Altitude Land use types Virgin forest Virgin savana Farming Park afforestation Grazing land Eucalyptus forest ANOVA pH H O High 5.35 ± .288 5.90 ± 0.20 5.21 ± 0.538 5.90 ± 0.200 5.57 ± 0.183 * Mid 5.63 ± 0.125 5.65 ± .057 5.48 ± 0.540 5.70 ± 0.159 6.10 ± .316 5.56 ± 0.130 * Low 6.50 ± 0.230 6.50 ± .000 5.87 ± 0.205 6.00 ± .496 5.77 ± 0.221 * Total 5.82 ± 0.551 6.02 ± .380 5.51 ± 0.520 5.70 ± .159 6.00 ± 0.335 5.61 ± 0.183 pH KCl High 4.45 ± o.288 4.65 ± 0.06 4.34 ± 0.27 4.65 ± 0.06 4.36 ± 0.23 * Mid 4.65 ± 0.10 4.50 ± 0.00 4.58 ± 0.06 4.46 ± 0.12 4.60 ± 0.22 4.56 ± 0.11 * Low 5.55 ± 0.17 5.30 ± 0.00 5.01 ± 0.32 4.88 ± 0.30 4.58 ± 0.15 * Total 4.88 ± 0.53 4.81 ± 0.36 4.63 ± 0.34 4.46 ± 0.12 4.71 ± 0.23 4.49 ± 0.19 Δ pH High − 0.90 ± 0.00 − 1.25 ± 0.17 − 0.88 ± 0.37 − 1.25 ± 0.17 − 1.21 ± 0.25 Mid − 0.98 ± 0.15 − 1.15 ± 0.06 − 0.91 ± 0.56 − 1.24 ± 0.14 − 1.50 ± 0.34 − 1.00 ± 0.16 Low − 0.95 ± 0.06 − 1.20 ± 0.00 − 0.86 ± 0.18 − 1.25 ± 0.38 − 1.20 ± 0.16 Total − 0.94 ± 0.09 − 1.20 ± 0.10 − 0.89 ± 0.41 − 1.24 ± 0.14 − 1.29 ± 0.32 − 1.13 ± 0.22 SOC (%) High 6.50 ± 1.62 4.83 ± 0.36 3.31 ± 0.57 4.83 ± 0.36 5.79 ± 2.11 * Mid 4.58 ± 1.61 2.10 ± 1.15 3.04 ± 0.87 2.83 ± 0.88 2.50 ± 0.83 3.46 ± 0.95 * Low 3.10 ± 0.81 3.10 ± 0.00 1.83 ± 0.90 1.90 ± 1.18 3.05 ± 0.53 * Total 4.73 ± 1.93 3.34 ± 1.33 2.77 ± 0.99 2.83 ± 0.88 3.08 ± 1.52 4.31 ± 1.89 C/N ratio High 21.91 ± 0.76 14.58 ± 2.39 13.06 ± 4.50 14.58 ± 2.39 24.74 ± 15.25 Mid 16.95 ± 8.63 9.10 ± 3.82 17.68 ± 6.53 12.05 ± 4.76 13.37 ± 6.31 17.36 ± 7.18 Low 11.18 ± 3.34 23.85 ± 0.00 8.65 ± 3.94 11.13 ± 9.31 14.00 ± 4.18 Total 16.68 ± 6.67 15.84 ± 6.78 13.78 ± 6.43 12.05 ± 4.76 13.03 ± 6.18 19.64 ± 11.28 TN (%) High 0.30 ± 0.06 0.34 ± 0.07 0.27 ± 0.06 0.34 ± 0.06 0.27 ± 0.11 * Mid 0.29 ± 0.08 0.22 ± 0.03 0.18 ± 0.03 0.25 ± 0.07 0.20 ± 0.03 0.21 ± 0.05 Ns Low 0.28 ± 0.01 0.13 ± 0.00 0.21 ± 0.05 0.19 ± 0.06 0.23 ± 0.04 Ns Total 0.29 ± 0.05 0.23 ± 0.09 0.21 ± 0.06 0.25 ± 0.07 0.24 ± 0.08 0.24 ± 0.08 Av.P (ppm) High 16.1 ± 3.00 19.1 ± 13.3 20.1 ± 10.3 19.1 ± 13.3 13.4 ± 7.19 Ns Mid 14.6 ± 3.74 15.6 ± 4.91 15.5 ± 7.65 9.83 ± 3.53 9.33 ± 4.16 11.1 ± 4.31 Ns Low 13.3 ± 2.25 5.30 ± 0.00 13.2 ± 5.61 8.90 ± 2.40 11.9 ± 2.39 Ns Total 14.6 ± 3.02 13.3 ± 9.59 16.1 ± 8.17 9.83 ± 3.53 12.4 ± 8.87 12.2 ± 5.28 Means in the same row followed by the same letters are not significantly different at 1% significance Ns non significance, MC moisture content, BD Bulk density * Significant at P < 0.01 Tellen and Yerima Environ Syst Res (2018) 7:3 Page 16 of 29 Table 5 Summary of ANOVA for pH, SOC, TN, and available P in relation to land use and elevation Source of variations df Av.P SOC TN C:N ratiopH H O MS P MS P MS P MS P MS P Land use (LU) 5 71.178 0.167 8.659 0.000 0.010 0.018 96.951 0.076 0.669 0.000 Elevation (E) 2 302.101 0.002 40.292 0.000 0.065 0.000 103.16 0.116 1.943 0.000 LU * E 8 39.388 0.892 2.539 0.035 0.008 0.027 149.80 0.003 0.286 0.008 Error 80 44.179 1.14 0.004 46.552 0.101 MS in the mean square, P is the p value, df is degree of freedom ANOVA for soil pH, SOC, TN, and Av.P in the 0–15 cm soil layer across different LULC systems and altitudes in the study area. Effects of land use change on soil pH H O, pH KCl and Δ pH The results also showed that soil pH significantly varied with land use types (P < 0.01) and across elevation (P  <  0.01) with significant interaction between subjects effects (P  <  0.01) (Table  4). According to Landon (1991) ratings, the soil pH for all the land uses in this study were low to medium (slightly acidic), probably due to the par- ent material (granitic) which is acidic in nature and are characteristic of oxisols. The results show that the soil under farmland use had relatively lower pH H O and pH KCl values and lower net charges compared to those of the other land uses/land cover systems in the area. In gen- Fig. 17 Estimated marginal means of pH KCl values in the 0–15 cm eral, soil pH decreased with increase in altitude (Figs. 16, soil layer across different land use/land cover systems and altitudes 17 and 18). This may be largely due to the use of chemical fertilizers including urea, potash, and N, K, P (20:10:10), as well as the high use of weedicides such as roundup, by farmers in the area which contain high amounts of cations that helps to neutralise the negative charges. The results show that there is a net negative charge for all the soils in Fig. 18 Estimated marginal means of net charge (Δ pH) values in the 0–15 cm soil layer across different land use/land cover systems and altitudes the area under study. The weathering of the granitic par - Fig. 16 Estimated marginal means of pH H 0 values in the 0–15 cm ent material, which results in iron and aluminum oxides, soil layer across different land use/land cover systems and altitudes as well as leaching of more soluble soil minerals and basic Tellen and Yerima Environ Syst Res (2018) 7:3 Page 17 of 29 cations, may have caused the slight acidity of the soils in soil, with increased efficiency as altitude increases, in the the study area. The net charge was less negative under North West Region of Cameroon. This result contradicts native forest systems compared to grazing, savanna, Euca- the findings of Kizilkaya and Dengiz (2010) who reported lyptus plantation and afforestation systems. a significant increase of pH from 6.03 in soils under natu - At high altitude, the soils under farmland use system ral forest to 7.71 in soils under cultivated land in Turkey. had the lowest mean pH value (5.2) while those under Although these are two different environments, this dif - natural savanna and grazing land had the highest mean ference may be due to the fact that sustainable agricul- pH value (5.9). At this altitude, mean pH values at the tural land management practices such as the application surface (0–15  cm) layer showed a significant difference of organic manure, mulching, rotation and limited tillage (P  <  0.01) between the soils under natural forest and were adopted in the cultivated land in Turkey while those natural savanna, as well as between those under farm- in our study area did not adopt sustainable land manage- land, natural savanna and grazing land use systems. The ment practices. It could also be due to the high basic fer- results also show that the soils under natural forest cover tilizer applications. Low soil pH impeds the CEC of the and E. saligna plantation had a relatively lower pH val- soil by altering the surface charge of colloids (finest clay ues (pH < 5.5) in this area. This is because Low pH slows particles and soil organic matter) (McCauley et al. 2005). down the breakdown of litter due to low microbiological Low CEC implies that soil will have less exchangeable activity (Yerima and Van Ranst 2005a). cations required as crop nutrients, nutrients are weekly Similarly, at mid-altitude, the soils under farmland use adsorbed and hence may be leached out. systems had the lowest mean pH value (5.4) followed by those under E. saligna plantation (5.5), while those under Effects of  land use change on  soil organic carbon (SOC) natural savanna and grazing land had the highest mean and organic matter (SOM) The results also showed that pH value (6.1). This similarity in pH values can be due SOC significantly varied with land use types (P < 0.01) and to the fact that the land use under natural savanna was with elevation (P < 0.01) but the interaction between sub- also used for cattle grazing. At this altitude, mean pH jects effects was not significant (P >  0.01) (Table  5). Fol- values at the surface (0–15  cm) layer showed a signifi - lowing the ratings by Yerima and Van Ranst (2005a), the cant difference (P  <  0.01) between the soils under farm - results show that all the soils under the different land use land and grazing land use systems, as well as between systems across the different elevations were medium to soils under E. saligna plantation and grazing land use high in SOC content. However, the percentage of OC con- system. The relatively high pH values under grazing centration for soils under natural forest as well as those land may be due to the high cow dung wastes depos- under E. saligna plantations were higher compared to all ited on the fields. Interestingly, at low altitude, the soils the other land use systems at all elevations (Fig.  19). In under E. saligna plantation had the lowest mean pH addition, the results indicate that OC in soils increased value (5.7) while those under natural forest and natural with increase in elevation in the N.W region. These results savanna had the highest mean pH value (6.5). Humphrey corroborate the findings of Yerima and Van Ranst (2005a). and Amawa (2014) also reported a similar finding in the study area. At this altitude, mean pH values at the surface (0–15 cm) layer showed a significant difference (P < 0.01) between the soils under natural vegetation (forest and savanna) cover and those under farmland and E. saligna plantation. Generally, the slightly acidic nature of the soils under all the land use/land cover systems may be due to the weathering of granitic parent materials and the intense leaching of basic cations. Also, the low pH values in farm- land could be due to high tillage frequency, high rates of inorganic fertilizer applications (especially ammonium fertilizers), low amount of organic matter as a result of erosion or due to aluminum toxicity. In fact, the sig- nificant differences of mean pH values at the surface (0–15 cm) layer between soils under cultivated land and those under natural vegetation across different altitudes Fig. 19 Estimated marginal means of soil organic carbon (%) in the indicates that the conversion of natural vegetation cover 0–15 cm soil layer across different land use/land cover systems and altitudes (forest and savanna) to farmland decreases pH of the Tellen and Yerima Environ Syst Res (2018) 7:3 Page 18 of 29 At high altitude, the soils under natural forest land matter mineralization associated with low temperatures cover system (protected forest) had the highest mean soil and decrease microbial activity. organic carbon content (6.50%) followed by those under At mid-altitude, the soils under natural forest land E. saligna plantations (5.79%) (Table  4). Those under cover systems still had the highest mean SOC content farmland use systems had the lowest mean percent- (4.58) followed by those under E. saligna plantation age of soil organic carbon content (3.31%). At this alti- (3.46%) (Table 4). Although the mean percentage of SOC tude, the mean percentage of SOC content at the surface contents for soils under farmland use systems were low (0–15 cm) layer showed a significant difference (P < 0.01) (3.04%), those under the natural savanna land use sys- between the soils under natural forest and farmland. tems had the lowest mean percentage (2.10%) compared Also, the results showed a significant difference (P < 0.01) to all the other land use/land cover systems. However, at between the soils under E. saligna plantations and those this altitude, the mean percentage of SOC content at the under farmland. However, there were no significant dif - surface (0–15  cm) layer showed significant differences ferences (P  >  0.01) between soils under natural savanna (P  <  0.01) between the soils under natural forest cover and grazing land. This may be due to the fact that the nat - and savanna, afforestation, and grazing land use systems. ural savanna land cover systems were observed to be sub- Although the natural savanna land cover system was jected to conditions similar to grazing land use (burning within the Yongka Garden Park, the results showed that and cattle grazing) in the area (Fig. 20). More so, the rela- the soil was low in soil organic carbon content compared tively higher soil organic carbon contents at higher eleva- to those under the natural forest cover. This can be sug - tions may be due to a slow down in the rate of organic gested to be due to the fact that the land was previously Fig. 20 Sheep and cattle grazing on grazing land (a); cattle grazing on Eucalyptus plantation (b); fire disturbance on grazing land (c); burnt tree trunks showing evidence of fire disturbance on Eucalyptus plantation (d) Tellen and Yerima Environ Syst Res (2018) 7:3 Page 19 of 29 used for cattle grazing, and soils in the area were gener- content compared to native ecosystems, since cultivation ally low in organic matter before the establishment of increases aeration of soil, which enhances decomposition the park (9 years old, after many years of cattle grazing), of soil organic matter (Kizilkaya and Dengiz 2010). due to unsustainable land use practices and soil degrada- These results conform to the assertion that SOC stocks tion. Results from interview with researchers from the are sensitive to land use and cover change (Guo and Gif- park, on the land use history of the area reveals that after ford 2002; Wiesmeier et al. 2012) probably because of the several years of intensive exploitation, prior to the estab- alterations of both carbon inputs (amount and quality lishment of the Park, mining of the soil organic carbon of litter mass) and losses (decomposition and minerali- and nutrient stocks was an issue, which led to a decline zation). Soil carbon improves the physical properties of in fertility, compaction of surface soils and slow and soil, increases the cation exchange capacity (CEC) and poor regeneration of vegetation on land left for fallow. water-holding capacity of the soil, and contributes to the They added that issues of water and fuelwood scarcity structural stability of soils by helping to bind particles in the nearby community were prominent at the time. into aggregates (Leeper and Uren 1993). It can be sug- This result is in line with the findings of Humphrey and gested that, anthropogenic activities that accentuate SOC Amawa (2014), who stated that intensification of agri - loss in the soil including tillage (hoeing, plowing), bio- culture and the use of inappropriate cultural practices mass burning, residual removal, overgrazing, and drain- including the cultivation on fragile (steep) hill-slopes, age, are responsible for the distribution of SOC contents setting of bushfires, overgrazing by cattle, building of observed, at different elevations, under the different land settlements, and increased consumption of the regions use/land cover systems in the N.W region. fuelwood, has lead to environmental and soil degradation Since carbon is a fundamental constituent of soil in the area. In fact, Yerima (2011) elucidated that soils in organic matter (Ogle et  al. 2005), the trends in effects the park are acidic in nature, have low nutrient contents of soil organic carbon under the different land use/land with compact and dense structures that are an impedi- cover systems in the N.W region mirrors that of SOM ment to plant growth. These are tangible reasons attract - and hence carbon storage of soil. It is well recognized ing afforestation initiatives and other sustainable land that SOM increases structural stability, resistance to use practices that promote conservation of biodiversity rainfall impact, the rate of infiltration and faunal activi - in the area. Hence, it is unarguable that the SOC values ties (Roose and Barthes 2001). SOM, of which carbon is reported in this study only presents a picture of the ongo- a major part, holds a great proportion of nutrients cati- ing land regeneration efforts that may require a longer ons and trace elements that are of importance to plant period of time to show its actual image. growth. According to Leu (2007), it prevents nutrient At low altitude, the soils under natural forest and those leaching and is integral to the organic acids that make under natural savanna land cover systems had the high- nutrients accessible to plants while acting as a soil buffer est mean soil organic carbon content (3.10%) followed to resist strong changes in pH. It is widely accepted that by soils under E. saligna plantations (3.05%) (Table  4). the carbon content of soil is a key element in its overall Those under farmland use systems had the lowest mean health (Yerima and Van Ranst 2005a). percentage of soil organic carbon content (1.83%). How- ever, at this altitude, the mean percentage of soil organic Effects of land use change on soil total nitrogen Soil total carbon content at the surface (0–15 cm) layer showed no nitrogen is typically used as an important index for soil significant differences (P > 0.01) between the soils under quality evaluation and reflects the soil nitrogen status all the land use/land cover systems. This can be attributed (Sui et al. 2005). Similar to soil organic carbon, soil total to the higher soil temperatures, which increases the rate nitrogen content (%) also exhibited obvious differences of mineralization due to increase in microbial activity. In at the surface (0–15  cm) layer under different land use/ addition, the area is located at the toe slope where the dif- land cover systems across the three elevations (Table  4). ference in slope gradient influences erosion, flooding and The results also showed that soil total nitrogen did not subsequent deposition of inorganic materials downslope. vary significantly with land use types (P < 0.01), but var - Deposition of inorganic materials through erosion bur- ied significantly with elevation (P  <  0.01). However, the ies the topsoil which is normally rich in organic matter, interaction between subjects’ effects was not significant hence the true picture of soil organic carbon is blurred (P < 0.01) (Table  4). Generally, the results show that soil at low altitude. As the soils under natural savanna were total nitrogen contents increase with an increase in eleva- subjected to grazing practices, it is possible that the soil tion in the N.W region (Fig. 21). samples collected were influenced by animal waste dep - The study showed that at high altitude, both the soils osition, hence the high SOC value recorded. Further- under savanna and grazing land use systems had the more, cultivated soils generally have low organic matter highest mean soil total nitrogen content (0.36%) followed Tellen and Yerima Environ Syst Res (2018) 7:3 Page 20 of 29 the surface (0–15 cm) layer showed no significant differ - ence (P > 0.01) between the soils under all the land use/ land cover systems. Although the level of nitrogen ferti- lizer use as agric-input was high in the region, the total nitrogen contents are low in farms, probably because of the poor nitrogen retention ability of the soils under farmland uses and the loss of organic matter which is a source of nitrogen. At low altitude, the soils under natural forest land cover systems also had the highest mean soil total nitrogen content (0.28%), while those under savanna land use had the lowest values (0.19%). At this altitude, mean soil total nitrogen at the surface (0–15  cm) layer showed significant differences (P  <  0.01) only between the soils under natural forest vegetation and those under natural savanna land cover systems. This can be due to Fig. 21 Estimated marginal means of nitrogen (%) in the 0–15 cm the fact that soils under savanna cover were disturbed by soil layer across different land use/land cover systems and altitudes human activities including; burning and grazing, which greatly influence the soil organic matter and hence soil nitrogen content. by those under natural forest cover (0.30%), while those under farmland system had the lowest. At this altitude, Effects of  land use change on  soil C/N ratio The results mean soil total nitrogen at the surface (0–15  cm) layer also show that the C/N ratio had no significant differences showed no significant difference (P  >  0.01) between the with land use types (P > 0.01) and with elevation (P > 0.01) soils under all the land use/land cover systems. It was but the interaction between subjects effects was signifi - observed that pasture density under grazing land use cant (P  <  0.01) (Table  4). However, the results indicate systems at the higher altitude was higher compared to an increase in C/N ratio with an increase in elevation in that at lower altitudes. This has a direct relationship with the N.W region except for soils under savanna and farm- organic matter content. Again, the similarities in results land use systems (Fig.  22). The quality of organic matter between savanna and grazing land may probably be due is expressed in form of the C/N ratio. According to rat- to the similarities in observed conditions (burning and ings by Yerima and Van Ranst (2005a), the results show cattle grazing) under the two land use systems in the that the quality of organic matter in all the soils under the area. The high amounts of nitrogen in soils under graz - different land use systems across the different elevations ing land may be due to the burning of grass that produce ranged between good quality, medium, and low quality. At ash which is rich in nitrogen and other major nutrients. It high altitude, the mean C/N ratio for soils under natural is well known that fire simulates cycling of nitrogen and thus, relatively high amounts of nitrogen in the ash could be found under such disturbed land use sites. Grazing land is also subjected to deposition of cow dung waste, which enhances the soil organic matter content. A high soil organic matter content strongly correlates with high nitrogen content. However, strong fires on sandy soils may give long-lasting loss of soil surface humus and nitrogen, which may lead to site impoverishment. Also, studies have suggested that grazing can promote nutri- ent cycling because livestock feces and urine provide large amounts of soluble nitrogen that is readily avail- able to plants for growth and livestock excretions can promote soil organic matter (SOM) mineralization rates (McNaughton et al. 1997). At mid-altitude, the soils under natural forest land cover system had the highest mean soil total nitrogen content (0.29%) while those under farmland had the low- Fig. 22 Estimated marginal means of C/N ratio in the 0–15 cm soil est (0.18%). At this altitude, mean soil total nitrogen at layer across different land use/land cover systems and altitudes Tellen and Yerima Environ Syst Res (2018) 7:3 Page 21 of 29 forest, savanna, and grazing land, as well as those under E. saligna plantations, reveals that the quality of organic matter was low (C/N > 14). Only soils under farmland had the medium quality of organic matter (C/N = 10–14). At mid-altitude, the mean C/N ratio for soils under savanna forest cover reveals that the organic matter was of good quality (C/N  <  10), while those for soils under afforestation plantations and grazing systems were of medium quality (C/N  =  10–14). However, those under natural forest, farmland and E. saligna plantations reveal that the quality of organic matter was low (C/N > 14). At low altitude, the mean C/N ratio for soils under farm- land reveals that the quality of organic matter was good (C/N  <  10), while those for soils under natural forest, E. saligna plantations and grazing land were of medium quality (C/N  =  10–14). However, those under natural Fig. 23 Estimated marginal means of available phosphorus (ppm) in the 0–15 cm soil layer across different land use/land cover systems forest cover reveals that the quality of organic matter was and altitudes low (C/N > 14). Soil C/N ratio is a sensitive indicator of soil quality. The soil C/N ratio is usually considered as an indicator at the surface (0–15 cm) layer showed no significant dif - of soil nitrogen mineralization ability. High C/N ratios ference (P  >  0.01) between the soils under all the land in soils can retard the rate of organic matter and organic use/land cover systems. These results are consistent with nitrogen decomposition by limiting the ability of soil the findings of Awdenegest et al. (2013). microbial actions, whereas low C/N ratios in soils could At mid-altitude, the soils under natural savanna, and accelerate the process of microbial decomposition of those under farmland had the highest mean soil avail- organic matter and nitrogen. However, Wu et  al. (2001) able phosphorus concentrations (15.6 and 15.5  ppm, reported that low soil C/N ratio is not conducive to car- respectively), while those under natural forest and E. bon sequestration. Therefore, it can be concluded that saligna plantation land cover systems were intermediate soils under natural forest, grazing land, and E. saligna (14.6 and 11.1  ppm, respectively). Those under affores - plantations slow down the decomposition rate of organic tation and grazing land use had the lowest values (9.83 matter and organic nitrogen by limiting the soil micro- and 9.33  ppm, respectively). It can be concluded here bial activity ability and can best sequester carbon in the that residue ash may have enhanced the P concentra- region as a means to combat climate change. tions under natural savanna, and those under farmland because burning was a cultural phenomenon under Effects of  land use change on  soil available phospho - these land use systems in the area. Also, the application rus Though not significant, the soil available phos - of chemical P-fertilizers and organic manure (poultry phorus also exhibited obvious differences at the surface manure and cow dung) may have enhanced the P con- (0–15 cm) layer under different land use/land cover sys - centrations in selected farmlands in this area. At this alti- tems (Table 4). However, the results indicate that concen- tude, mean soil available phosphorus concentrations at trations of soil available phosphorus varied significantly the surface (0–15 cm) layer showed no significant differ - (P  <  0.01) with elevation, indicating a decrease with a ence (P > 0.01) between the soils under all the land use/ decrease in elevation in the N.W region (Fig. 23) although land cover systems. the interaction effect between subjects was not significant At low altitude, the soils under natural savanna, and (P > 0.01). those under farmland had the highest mean soil available The study showed that at high altitude, the soils under phosphorus concentrations (15.6 and 15.5  ppm, respec- farmland use systems had the highest mean soil available tively), while those under natural forest land cover were phosphorus concentrations (20.1 ppm) followed by those intermediate (14.6  ppm), while those under savanna under savanna and grazing land use system (19.1  ppm), land use had the lowest values (5.30  ppm). At this alti- while those under E. saligna plantation land use had the tude, mean soil available phosphorus concentrations at lowest value (13.4 ppm) (Table 4). This can be due to the the surface (0–15  cm) layer showed no significant dif - fact that farmers applied fertilizers such as Diammonium ference (P  >  0.01) between the soils under all the LULC phosphate (DAP) on their farmlands. However, at this systems. It is suggested that the relatively lower available altitude, mean soil available phosphorus concentrations Tellen and Yerima Environ Syst Res (2018) 7:3 Page 22 of 29 phosphorus concentrations in the protected forest and E. saligna plantations at all elevations may be related to phosphorus fixation due to the relatively higher organic matter concentrations under these land use systems. This result agrees with the findings of Yimer et al. (2008) who reported higher concentrations of P in soils of the native forest than those of cropland and grazing in the Bale Mountains of Ethiopia. According to ratings by Yerima and Van Ranst (2005a), available phosphorus across all land uses was very low, except those in the top 0–15  cm soil layer of farmlands, at high altitude which was low. In addition, the avail- able phosphorus in soils under all the land uses in the study area falls below the medium sufficiency range of 26–54  mg/kg suggested by Carrow et  al. (2004). The available phosphorus deficiency in soils of our study Fig. 24 Estimated marginal means of cation exchange capacity in area may be due to the inherent low-P status of the par- the 0–15 cm soil layer across different land use/land cover systems and altitudes ent material and erosion loss. This may also be due to the low soil pH which causes P-fixation. These results con - firm the findings of Yerima and Van Ranst (2005b) who under afforestation in the park had the lowest values reported that the available phosphorus in most soils of (19.7  cmol (+)/kg soil). Also, at this altitude, mean con- the North West region is low due to P-fixation, crop har - centration of CEC of soils at the surface (0–15 cm) layer vest, and erosion by water. showed no significant difference (P  >  0.01) between the soils under all the land use/land cover systems. Effects of  land use change on  cation exchange capacity At low altitude, the soils under savanna land cover (CEC, cmol (+)/kg soil) CEC also exhibited some differ - systems had the highest mean CEC concentration ences at the surface (0–15 cm) layer under different land (34.1  cmol (+)/kg soil) followed by those under natural use/land cover systems, although not significant. Also, forest (24.0  cmol (+)/kg soil) while those under farming there were no significant differences (P > 0.01) with eleva - land use systems had the lowest values (17.7  cmol (+)/ tions and the interaction between subjects effects was not kg soil). At this altitude, mean CEC concentration of significant (P < 0.01) (Table  4). Generally, the results did soils at the surface (0–15  cm) layer showed a significant not show a clear picture of the variation of CEC of soils difference (P  <  0.01) only between the soils under natu - under different land use/land cover systems with eleva - ral savanna vegetation cover and farmland use systems. tion, in the N.W region (Fig. 24). Generally, according to ratings by Landon (1991), the The study shows that at high altitude, both the soils CEC values in soils under all the land use/land cover sys- under savanna and grazing land use systems had the tems, were medium except those under natural forest and highest mean concentration of CEC (23.1  cmol (+)/ savanna land use cover at mid and low elevations, respec- kg soil), followed by those under farmland (19.7  cmol tively which were high. (+)/kg Soil), while those under E. saligna plantation and natural forest cover were relatively lower (17.6 and Effects of land use change on electrical conductivity (mS/ 16.3  cmol (+)/kg soil, respectively) (Table  4). However, cm) EC values ranged from 0.05 mS/cm under grazing at this altitude, mean CEC concentration of soils at the land use systems to 0.18 mS/cm under natural forest veg- surface (0–15 cm) layer showed no significant difference etation. Generally, the results show that EC varied signifi - (P  >  0.01) between the soils under all the land use/land cantly (P > 0.01) with land use, but showed no significant cover systems. These results contradict the findings of difference in elevation (Table  6). Also, the interaction Awdenegest et al. (2013) who reported that the CEC con- effects between subjects were not significant. At all ele - centration was low in oxisols under savanna and grazing vations, mean EC values at the surface (0–15  cm) layer land use systems compared to farmland use systems in showed significant differences (P < 0.01) between the soils Southern Ethiopia. under natural forest and those of the other land use/land At mid-altitude, the soils under natural forest land cover systems (Fig. 10). More so, although the EC content cover systems had the highest mean concentration of in soils under farmland were not significantly different CEC (25.8  cmol (+)/kg soil) followed by those under E. (P  >  0.01) from those for soils under the other land use saligna plantations (24.7  cmol (+)/kg soil), while those Tellen and Yerima Environ Syst Res (2018) 7:3 Page 23 of 29 Table 6 Summary of ANOVA for EC, exchangeable cations and CEC in relation to land use and elevation + + 2+ 2+ Source of variations df ECEx. NaEx. KEx. CaEx. Mg CEC MS P MS P MS P MS P MS P MS P Land use (LU) 5 0.016 0.000 0.063 0.681 3.842 0.65 6.734 0.248 2.958 0.091 92.832 0.332 Elevation (E) 2 0.003 0.029 0.077 0.472 13.786 0.001 51.454 0.000 11.39 0.001 105.58 0.271 LU * E 8 0.001 0.209 0.136 0.235 3.182 0.089 26.472 0.000 2.521 0.114 79.766 0.440 Error 80 0.001 0.102 1.768 4.949 1.493 79.446 MS is the mean square, P is the p value, df is degree of freedom systems (except those under natural forest vegetation) at all elevations (high, mid and low), the soils under natural forest had higher EC values (0.18, 0.17 and 0.12  mS/cm, respectively) than those of the other land use/land cover systems (Fig.  25). Therefore, the conversion of forest to cultivated land decreases EC in the study area. These results are in line with the findings of Kizilkaya and Den - giz (2010) who reported that changing forest to cultivated land increased EC values in their area of study due to high application rates of chemical fertilizers. Although EC represents soil soluble salt components, it is believed that the use of basic chemical fertilizer such as ammonium phosphate and urea under farmlands in our study area did not lead to higher EC values above normal (EC  >  0.15 mS/cm will affect plant growth and develop - Fig. 25 Estimated marginal means of electrical conductivity in the ment) when compared to those under natural forest cov- 0–15 cm soil layer across different land use/land cover systems and ers. Therefore, farmers must avoid complete reliance on altitudes chemical inputs but continue to rely more on organic fertigation to keep EC < 0.15 in soils. In this regards, the soils under natural forest at high and mid-altitudes in this study may affect the growth and development of only some EC sensitive plants species since their EC concen- trations are slightly above normal. Effects of  land use change on  exchangeable bases Exchangeable sodium (Na ) (cmol (+)/kg soil) Generally, the results show that mean soil exchangeable Na had no significant differences with land use types (P > 0.01) and across all elevations (Table 6). The concen - tration of exchangeable N a was the smallest component on the exchange complex. In addition, the interaction between subject effects was not significant (P   >  0.01). Although there was no significant differences (P  < 0.01) at the surface (0–15  cm) layer, at high altitude, soils under the protected forest had the highest mean soil exchange- able Na concentrations (1.05 cmol (+)/kg soil) followed Fig. 26 Estimated marginal means of exchangeable Na in the by the soils under farmlands (1.01 cmol (+)/kg soil), while 0–15 cm soil layer across different land use/land cover systems and those under savanna and grazing land use systems had altitudes lower values (0.65 and 0.67, respectively) (Fig. 26). Tellen and Yerima Environ Syst Res (2018) 7:3 Page 24 of 29 This result corroborate the findings of Yimer et  al. (2008) who reported that the concentration of soil exchangeable Na was lower in cropland than in the grazing and native forest. Alem et  al. (2010) also observed higher soil exchangeable N a concentration in soils under E. grandis when compared to those of native forest in Ethiopia. Significantly high concentra - tions of exchangeable Na in the soil in, particularly in proportion to the other cations present, can have an adverse effect on crops and physical conditions of the soil (Yerima and Van Ranst 2005a; Bashour and Sayegh 2007). Although Adetunji (1996) indicated that soils with exchangeable N a of 1  cmol (+)/kg soil should be regarded as potentially sodic, those under native for- est in the study cannot be regarded as sodic soils, since the soil pH was slightly acidic, and there were no exist- Fig. 27 Estimated marginal means of exchangeable K in the ing evidence of soluble salts in the area. In fact, the con- 0–15 cm soil layer across different land use/land cover systems and centration of exchangeable Na in the other land use altitudes systems did not attain 1  cmol (+)/kg soil. The alternate wet and dry seasons and the topographic (drainage) con- layer showed significant differences (P  <  0.01) between ditions may be responsible for the potential sodicity value the soils under natural forest and all the other land use recorded under the protected forest systems in this study. systems except farmland. At mid-altitude, soils under At mid-altitude, soils under the grazing land use had the protected natural forest also had the highest mean the highest mean soil exchangeable N a concentrations soil exchangeable K concentration (1.75  cmol (+)/kg (0.88  cmol (+)/kg soil) followed by the soils under E. soil) followed by the soils under farmlands (1.05  cmol saligna plantations (0.86  cmol (+)/kg soil), while those (+)/kg soil), while those under savanna and grazing land under protected forest and savanna land cover systems use had the lowest concentration (0.25 cmol (+)/kg soil). had the lowest concentrations (0.65  cmol (+)/kg soil). However, at this altitude, mean soil exchangeable K However, at this altitude, mean soil exchangeable N a concentration at the surface (0–15  cm) layer showed no concentrations at the surface (0–15 cm) layer showed no significant difference (P  >  0.01) between the soils under significant difference (P  >  0.01) between the soils under all the land use/land cover systems. all the land use/land cover systems. At low altitude, soils At low altitude, soils under the savanna land use system under the natural forest land use system had the highest also had the highest mean exchangeable K concentra- mean soil exchangeable N a concentrations (0.85  cmol tion (3.10  cmol (+)/kg soil) followed by the soils under (+)/kg soil) while those under E. saligna plantation had farmlands (2.49 cmol (+)/kg soil) while those under nat- the lowest concentration (0.58 cmol (+)/kg soil). This ural forest cover and grazing land use had the lowest con- may be due to the fact that the low soil pH under the centrations (1.90 and 1.83 cmol (+)/kg soil, respectively). Eucalyptus plantation would lead to a decrease in soil At this altitude, mean soil exchangeable K concentra- base saturation, through immobilization of the exchange- tion at the surface (0–15 cm) layer showed no significant able bases, and may result in soil exchangeable bases difference (P > 0.01) between the soils under all the land depletion over time (Aweto and Moleele 2005). use/land cover systems. The observed high concentra - Exchangeable potassium (K , cmol (+)/kg soil) tions of soil exchangeable K under the natural forest The results showed that soil exchangeable K did not land use system can be attributed to a relative pumping significantly vary with land use types (P > 0.01) but varied of potassium from the subsoil to topsoil by vegetation significantly with elevation (P < 0.01) (Table  6). However, (Bohn et  al. 2001). Also, the observed high concentra- the interaction between subject effects was significant tion of soil exchangeable K under the cultivation land (P  >  0.01). At high altitude, soils under the protected use system can be attributed to the observed frequent forest had the highest available potassium concentra- application of household wastes, particularly wood ash, tion (4.00  cmol (+)/kg soil) followed by the soils under as well as burning of farm residues. These results are con - farmlands (2.94  cmol (+)/kg soil), while those under sistent with the findings of Bohn et  al. (2001). Accord - savanna and grazing land use had the lowest concentra- ing to ratings by Landon (1991), soil exchangeable K tions (1.05  cmol (+)/kg soil) (Fig.  27). At this altitude, concentration under the natural forest land use system mean soil available potassium at the surface (0–15  cm) Tellen and Yerima Environ Syst Res (2018) 7:3 Page 25 of 29 and those under all the other land use systems was high the surface (0–15  cm) layer showed no significant dif - across the different elevations except those in grazing ference (P  >  0.01) between the soils under all the land land at mid-altitude which was medium. The medium use/land cover systems. At low altitude, soils under the soil exchangeable K concentrations under grazing land natural savanna land use systems had the highest mean 2+ could be associated with soil degradation and losses due exchangeable Ca concentration (8.50 cmol (+)/kg soil), to leaching as the grazing land was denuded of vegeta- followed by the soils under E. saligna plantation (4.98 tion cover. A critical concentration of 0.12  cmol/kg soil cmol (+)/kg soil), while those under natural forest cover is required for plant growth on oxisols (Yerima and Van had the lowest concentration (2.85  cmol (+)/kg soil). At 2+ Ranst 2005b) and the results indicate that exchangeable this altitude, mean soil exchangeable C a at the surface K concentration is not limiting in the soils of the study (0–15 cm) layer showed significant differences (P < 0.01) area. between the soils under natural forest, savanna, and 2+ Exchangeable calcium (Ca , cmol (+)/kg soil) farmland. 2+ The results showed that soil exchangeable Ca con- According to ratings by Landon (1991), soil exchange- 2+ centrations did not significantly vary with land use able Ca concentrations in the protected forest and type (P  >  0.01) but varied significantly with elevation farmland as well as those under savanna and grazing land (P  <  0.01) (Table  6). However, the interaction between and E. saligna plantation in the high and low altitudes subject effects was significant (P  <  0.01). At high alti - respectively, was medium, while the soil exchangeable 2+ tude, soils under the protected forest had the highest Ca concentrations under all the other land use sys- 2+ mean exchangeable C a concentration (8.25  cmol (+)/ tems across the different altitudes was low. The medium 2+ kg soil) followed by the soils under farmlands (6.00 cmol soil exchangeable Ca in the protected forest, farmland, (+)/kg soil), while those under savanna and grazing land grazing land and E. saligna plantation was probably due use had the lowest (2.00  cmol (+)/kg soil) (Fig.  28). At to the application of household wastes (wood ash in par- 2+ this altitude, mean soil exchangeable C a at the surface ticular) in the fields as well as the burning of floral and 2+ + (0–15 cm) layer showed significant differences (P < 0.01) crop residues since ash is a good source of C a, K , P, 2+ between the soils under natural forest and all the other and Mg (Voundi et  al. 1998) and pumping of bases land use systems except those under farmland. from the subsoil by the vegetation and returning them At mid-altitude, soils under the protected natural for- into the topsoil (Yimer et  al. 2008). On the other hand, 2+ 2+ est also had the highest mean soil exchangeable Ca the low soil exchangeable C a could be as a result of soil concentrations (3.68  cmol (+)/kg soil) followed by the erosion and nutrient losses through leaching as the graz- soils under E. saligna plantation (2.20  cmol (+)/kg soil), ing land was denuded of vegetation cover. A critical con- while those under savanna land cover had the lowest centration of 0.2 cmol/kg soil is required for plant growth concentration (0.80  cmol (+)/kg soil). However, at this in tropical soils (Landon 1991) and the results indicate 2+ 2+ altitude, mean soil exchangeable Ca concentrations at that exchangeable C a is not limiting in the soil of study area. 2+ Exchangeable magnesium (Mg , cmol (+)/kg soil) The results also showed that the concentrations of 2+ soil exchangeable M g did not vary significantly with land use type (P  >  0.01) but significantly differed with altitude (P  <  0.01) (Table  6) with the lowest concentra- tions at mid-altitude (Table  7). More so, the interaction between subject effects was not significant (P > 0.01). At high altitude, soils under protected forest had the highest 2+ mean exchangeable M g concentrations (3.35 cmol (+)/ kg soil) followed by the soils under farmlands (2.69 cmol (+)/kg soil), while those under savanna and grazing land use had the lowest concentrations (0.93 cmol (+)/kg soil) 2+ (Fig.  29). At this altitude, mean soil exchangeable Mg concentration at the surface (0–15 cm) layer showed sig- nificant differences (P  <  0.01) between the soils under natural forest and all the other land use systems, except 2+ those under farmland. Fig. 28 Estimated marginal means of exchangeable Ca in the 0–15 cm soil layer across different land use/land cover systems and At mid-altitude, soils under the protected natural for- 2+ altitudes est also had the highest soil mean exchangeable M g Tellen and Yerima Environ Syst Res (2018) 7:3 Page 26 of 29 Table 7 Mean (± SD) of soil EC, exchangeable cations and CEC in the 0–15 cm soil layer across different land use/land- cover systems and altitudes Soil property Altitude Land use types Virgin forest Virgin savana Farming Park afforesta- Grazing land Eucalyptus ANOVA tion forest Ex. Na (cmol (+)/ High (> 1500 m) 1.05 ± 0.17 0.65 ± 0.06 1.01 ± 0.51 0.67 ± 0.29 0.70 ± 0.21 Ns kg Soil) Mid (900–1500 m) 0.65 ± 0.33 0.65 ± 0.29 0.68 ± 0.23 0.67 ± 0.29 0.88 ± 0.06 0.86 ± 0.44 Ns Low (< 900 m) 0.85 ± 0.52 0.70 ± 0.00 0.68 ± 0.35 0.88 ± 0.21 0.58 ± 0.35 Ns Total 0.85 ± 0.38 0.67 ± 0.16 0.77 ± 0.38 0.67 ± 0.29 0.70 ± 0.29 0.74 ± 0.35 Ex. K (cmol (+)/ High (> 1500 m) 4.00 ± 0.23 1.05 ± 0.64 2.94 ± 1.82 0.74 ± 0.22 1.40 ± 1.40 * kg Soil) Mid (900–1500 m) 1.75 ± 1.57 0.25 ± 0.17 1.05 ± 0.46 0.45 ± 0.24 0.65 ± 0.30 1.04 ± 0.79 Ns Low (< 900 m) 1.90 ± 0.35 3.10 ± 0.00 2.49 ± 3.08 1.83 ± 1.59 2.43 ± 2.02 Ns Total 2.55 ± 1.37 1.47 ± 1.30 2.00 ± 2.04 0.45 ± 0.24 1.18 ± 1.04 1.46 ± 1.37 2+ Ex. Ca (cmol High (> 1500 m) 8.25 ± 0.17 2.00 ± 0.60 6.00 ± 3.24 2.00 ± 0.60 2.93 ± 2.87 * (+)/kg Soil) Mid (900–1500 m) 3.68 ± 2.79 0.80 ± 0.12 1.80 ± 0.79 1.28 ± 0.63 2.18 ± 1.69 2.20 ± 1.59 Ns Low (< 900 m) 2.85 ± 0.29 8.50 ± 0.00 3.63 ± 3.64 4.50 ± 3.54 4.98 ± 4.84 Ns Total 4.93 ± 2.88 3.77 ± 3.55 3.52 ± 3.09 1.28 ± 0.63 2.89 ± 2.39 3.05 ± 2.96 2+ Ex. Mg (cmol High (> 1500 m) 3.35 ± 0.17 0.93 ± 0.55 2.69 ± 1.63 0.93 ± 0.55 1.23 ± 1.20 (+)/kg Soil) Mid (900–1500 m) 1.60 ± 1.44 0.25 ± 0.17 0.98 ± 0.42 0.43 ± 0.21 0.60 ± 0.24 0.94 ± 0.20 Low (< 900 m) 1.70 ± 0.35 2.90 ± 0.00 2.36 ± 2.91 1.73 ± 1.46 2.28 ± 1.86 Total 2.22 ± 1.15 1.36 ± 1.21 1.86 ± 1.89 0.43 ± 0.21 1.08 ± 0.97 1.32 ± 1.23 EC High (> 1500 m) 0.18 ± 0.01 0.07 ± 0.01 0.08 ± 0.02 0.07 ± 0.02 0.08 ± 0.03 * Mid (900–1500 m) 0.17 ± 0.03 0.08 ± 0.01 0.07 ± 0.02 0.06 ± 0.01 0.05 ± 0.00 0.07 ± 0.03 * Low (< 900 m) 0.12 ± 0.06 0.06 ± 0.00 0.07 ± 0.04 0.07 ± 0.05 0.06 ± 0.01 * Total 0.16 ± 0.05 0.07 ± 0.01 0.08 ± 0.03 0.06 ± 0.01 0.06 ± 0.03 0.07 ± 0.02 CEC (cmol (+)/kg High (> 1500 m) 16.3 ± 5.32 23.1 ± 10.9 19.4 ± 12.6 23.1 ± 10.9 17.6 ± 6.78 Ns Soil) Mid (900–1500 m) 25.8 ± 14.2 22.8 ± 9.06 22.8 ± 6.88 19.7 ± 7.38 20.7 ± 1.79 24.7 ± 9.6 Ns Low (< 900 m) 24.0 ± 12.2 34.1 ± 0.00 17.7 ± 8.30 19.6 ± 11.5 22.5 ± 7.44 * Total 22.0 ± 11.1 26.7 ± 9.21 20.4 ± 9.11 19.7 ± 7.38 21.1 ± 8.49 21.4 ± 8.43 Means in the same row followed by the same letters are not significantly different at 1% significance Ns non significance, MC moisture content, BD Bulk density * Significant at P < 0.01 concentrations (1.60 cmol (+)/kg soil) followed by the soils under farmland (0.98 cmol (+)/kg soil), while those under savanna land cover had the lowest concentra- tions (0.25 cmol (+)/kg soil). More so, at this altitude, 2+ mean soil exchangeable M g concentrations at the sur- face (0–15 cm) layer showed no significant difference (P  >  0.01) between the soils under all the land use/land cover systems. At low altitude, soils under the natural savanna land use system had the highest mean exchange- 2+ able Mg concentration (2.90 cmol (+)/kg soil) followed by the soils under farmland (2.36 cmol (+)/kg soil), while those under natural forest cover had the lowest concen- tration (2.85  cmol (+)/kg soil). At this altitude, mean 2+ soil exchangeable Mg at the surface (0–15 cm) layer showed no significant differences (P < 0.01) between the 2+ soils under all the land use/land cover systems. Fig. 29 Estimated marginal means of exchangeable Mg in the Generally, the results for exchangeable bases follow 0–15 cm soil layer across different land use/land cover systems and altitudes a similar trend and hence the simultaneous explanation Tellen and Yerima Environ Syst Res (2018) 7:3 Page 27 of 29 provided above is believed to provide justifications for Table 9 Correlation matrix table for selected soil pH and exchangeable acidity at surface 0–15 cm soil depth these dynamics. According to ratings by Landon (1991), 2+ soil exchangeable M g concentration in all the land use/ pH EA land cover systems was medium, except for those under pH 1 − 0.752** savanna and afforestation in the mid-altitude, which was EA − 0.752** 1 less than the critical level of 0.5 cmol (+)/kg soil. A con- ** Correlation is significant at the 0.01 level; EA is exchangeable acidity centration less than the critical level would require an application of magnesium limestone for management accordingly (Awdenegest et al. 2013). manage the acidity problems, while the observed mod- erate and lower EA values indicates the easiness to also Effects of  LULC change on  soil exchangeable acidity manage the acidity problem of the respective land uses + 3+ (H   +  Al ) The laboratory results showed that some and elevations, within the study area. soils under natural forest cover, farmland and E. saligna According to the Apal Agricultural Laboratory; soil plantations, particularly at high and mid-altitudes, had test interpretation guide (2016), where extractable alu- relatively lower pH values (pH < 5.5), though only mean minum is  >  2, sensitive plants will be affected. It also pH concentrations of soils under farmland are indicated 3+ states that excess soluble/available aluminum (Al ) is in Table  4. These soils were selected and analysed for toxic to plants and can cause a number of problems. The exchangeable acidity (EA) and the results are presented 3+ guide further explains that some issue caused by Al in Table 8. toxicity can include: direct toxicity, primarily seen as It has been well reported that high exchangeable acid- stunted roots; reduction of the availability of phosphorus, ity occurs in very acidic soils, with low pH values (Yer- through the formation of Al-P compounds; reduction of ima and Van Ranst 2005a; Aweto and Moleele 2005). the availability of sulfur, through the formation of Al-S 3+ The hydrolysis of Al ions that constitute part of the compounds; reduction of the availability of other cations clay layers become exchangeable and contribute to 2+ 2+ (Ca and Mg ) through competitive interactions; and the development of soil acidity (Yerima and Van Ranst reduced rhizobium levels on legumes. The high EA under 2005a; Oyedele et  al. (2009). In fact, correlation analysis eucalyptus plantations confirms the low yields observed (Table  9) shows a significantly strong negative relation - for most crops planted around eucalyptus plantations ship (r  =  −  0.752, P  <  0.01) between soil pH and soil and confirms the acidifying nature of eucalyptus leaves exchangeable acidity. Frimpong et al. (2014) stated that at under decomposition. The high EA values in farmland pH below 5.5, aluminum and manganese toxicities might are consistent with the acidification resulting from the occur. application of ammonium fertilizers (Yerima and Van At high altitude, soils under farmland and Eucalyptus Ranst 2005a, b). plantations had high EA values (Ex. Acidity > 2), while at mid-altitude, only those under farmland had a high EA Conclusions value (Table  8). These results indicate that at high alti - This study was aimed at assessing the effects of six land tudes, soils under farmland and Eucalyptus plantations use systems on fifteen soil physicochemical properties in as well as those under farmland at mid-altitude, present the North West region of Cameroon. Ninety soil samples a high potential for aluminum toxicity to plants and may were collected from each land use system at the 0–15 cm have immobilized soil essential nutrients. Aweto and depth for laboratory analysis. The findings suggest that Moleele (2005) reported that soils with higher exchange- LULC change has influenced many soil physicochemical able acidity cause immobilization of soil essential nutri- properties at different topographic altitudes in the North ents including; P, N, Ca, Mg, and K under Eucalyptus spp. West region of Cameroon. The conversion of natural The observed high values of EA indicates a difficulty to forest or savanna to farmland reduced the silt contents, + 3+ Table 8 Means of selected soil exchangeable acidity (H +Al ) in the 0–15 cm soil layer across different land use/land cover systems and altitudes Factor Altitude Land use types Virgin forest Virgin savana Farming Park afforestation Grazing land Eucalyptus forest EA High (> 1500 m) 1.5 – 3.07 – – 3 Mid (900–1500 m) 1.6 – 2.6 – – 1.82 Low (< 900 m) – – – – 0.4 – Tellen and Yerima Environ Syst Res (2018) 7:3 Page 28 of 29 Consent for publication moisture content, organic matter, soil organic carbon, All authors read the manuscript and agree to publication. total nitrogen, available phosphorus, pH, cation exchange capacity, and exchangeable bases, but increased the soil Declaration I, Valentine Asong Tellen, holder of ORCID number 0000-0001-8513-788X bulk density, electrical conductivity, exchangeable acid- hereby declare that this research article is written by the authors whose ity and sand content significantly (P  <  0.05). The results names have been appropriately indicated. revealed that deforestation and subsequent cultivation Ethics approval and consent to participate of soil had negative effects on the measured soil proper - The authors hereby declare that, this manuscript is not published or consid- ties. Therefore, it can be concluded that the conversion ered for publication elsewhere. of natural forest or pasture land to cultivation land sub- Funding jected soil physicochemical properties to degradation Self-funded. thereby sullying soil quality. To reverse soil degradation and promote restoration in the region, emphases should Publisher’s Note be placed on promoting site-specific, sustainable land Springer Nature remains neutral with regard to jurisdictional claims in pub- management practices within the savanna, grazing, agri- lished maps and institutional affiliations. cultural and forest management systems. Received: 29 June 2017 Accepted: 16 January 2018 The scope of this research was limited to only three subdivisions (Santa, Bamenda, and Ndop) under just two divisions (Mezam and Ngoketungia) but gives a repre- sentation of the geomorphic surfaces in the NW region of Cameroon. The research also used only selected soil References Adetunji MT (1996) Field soil tests for NO3, NH4, PO4, K, Ca and Na. Depart- physical and chemical properties as indicators of soil ment of Soil Science and Mechanization, University of Abeokuta, Nigeria. quality under the influence of land use change. Generally, In: Simple Soil, Water and Plant Testing Techniques for Soil Resource soil quality varies greatly with soil type, depth and over a Management. Proceedings of a Training Course Held in Ibadan, Nigeria, 16–27 September 1996. 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Published: Jan 25, 2018

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