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Characteristics of Nitisol profiles as affected by land use type and slope class in some Ethiopian highlands

Characteristics of Nitisol profiles as affected by land use type and slope class in some... Background: The success of soil management depends on understanding of how soils respond to agricultural land use practices over time. Nitisols are among the most extensive agricultural soils in the Ethiopian highlands but soil degradation threatens their productive capacity. In this study, the effects of two land use systems, intensive cereal and agroforestry systems, and slope class on physical and chemical characteristics of some Nitisol profiles were investigated. In total 12 sample profiles were described and soil samples were collected from each of the identified master horizon. Soil physical characteristics evaluated were particle size distribution, structural aggregate stability, water holding capacity and bulk density. Chemical characteristics determined were exchangeable bases and cation exchange capacity, soil pH and the contents of organic carbon (OC), total nitrogen ( TN), available phosphorus (AP) and some micronutrients. Results: Among the physical characteristics, land use and slope significantly (p < 0.05) affected particle size distribu- tion and plant available water content. The mean sand (28%) and silt (26%) particles in the intensive cereal system were significantly (p < 0.05) higher compared to 15% sand and 18% silt in the agroforestry system. Conversely, the mean values of fine grained texture materials including 39% fine sand, 42% fine silt and 67% clay in the agroforestry system were significantly higher than 30% fine sand, 21% fine silt and 46% clay in the cereal system. Similarly, the lower slope had significantly (p < 0.05) higher fin texture materials (39% fine sand, 30% fine silt, and 63%) clay) com- pared to 17% fine sand, 14% fine silt and 51% clay fractions in the upper slope. The proportion of water stable aggre - gate ( WSA) were highlight (63–94%) and there was no significant difference between land types and slope classes. Following from high structural aggregate stability, the soils have high water holding capacity that ranged from 22 to −1 32% at PWP to 34–49% at FC while plant available water content (AWC) was in the 120–230 mm m range. Consider- ing the chemical characteristics, land use significantly affected soil pH, total nitrogen ( TN), exchangeable magnesium 2+ + 2+ 2+ (Mg ), potassium (K ), percent base saturation (PBS), and available micro nutrients—iron (Fe ), manganese (Mn ) 2+ and zinc (Zn ). The mean pH value (5.29) in the intensive cereal system strongly acidic while the pH value for the agroforestry system (6.12) was taken moderately acidic. The mean OC content was 2.0 and 2.1% for the intensive cereal and agroforestry systems that were rated very low. The mean TN values were 0.15 and 0.22% for intensive cereal −1 and agroforestry systems that were taken as low to very low. Similarly the mean values for AP were 8 and 10 mg kg 2+ 2+ for cereal and agroforestry systems that were rated low. On the other hand, the CEC, exchangeable bases ( Ca, Mg , + + K ) and PBS of the soil were rated high while Na appeared only in trace amount, and there was no significant differ - 2+ + 2+ + ence between land use type and slope classes except for Mg , K and PBS. Mean values of Mg and K (15 and 3 −1 cmol(+) kg ) and PBS (75%) in the agroforestry system were significantly higher than those in the cereal system (6 −1 2+ + and 1.6 cmol(+) kg of Mg and K and 51% PBS). Among micronutrients, land use significantly (p < 0.05) affected *Correspondence: Eyasu.elias@aau.edu.et; eyuelias@gmail.com Centre for Environmental Science, College of Natural and Computational Sciences, Addis Ababa University, Addis Ababa, Ethiopia © The Author(s) 2017. 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. Elias Environ Syst Res (2017) 6:20 Page 2 of 15 2+ 2+ + 2+ −1 2+ −1 available Fe, Mn and Zn . The mean values of Fe (97 mg kg ) and Mn (68 mg kg ) in the agroforestry −1 system were taken as excessively high while they were moderately sufficient (37, 39 mg kg , respectively) in the cereal system. Slope effects were significant for OC, TN and AP having higher mean values (2.5% OC, 0.22% TN and −1 −1 17 mg kg AP) in the lower slope than in the upper slope (1.5% OC, 0.13% TN and 8 mg kg AP). Conclusion: Land use and slope had significant effect on some soil physical and chemical characteristics. The land use practices in the intensive cereal system are adversely affecting important soil characteristics as compared to the soil under the agroforestry system. These include alteration of particle size distribution, strongly acidic soil reaction, organic matter and nutrient depletion (N, P, K and Zn) and low plant available water content. Among the inappro- priate land use practices include repeated cultivation to create fine seedbed that predisposes the soil to erosion, unbalanced fertilizer application, rotation of maize with potato that are depleting soil nutrient stocks (e., K and Zn), and removal of crop residues from fields. Therefore, a more balanced fertilizer blend application that contain N, P, K and Zn combined with liming to raise soil pH, organic matter management and integrated soil water conservation are recommended. Keywords: Land use, Nitisol profiles, Physical and chemical characteristics, Slope use changes and cultivation of fields without adequate Background conservation practices, low levels of fertilizer application In Ethiopia, diversities in state factors such as topog- and failure to recycle crop residues are among the causal raphy, parent materials, climate and vegetation have factors. Traditionally, soil fertility is replenished through resulted in the development of 18 soil types of which fallow cycles of up to 20 years during which time the land Nitisols are among the most extensive soils (FAO 1984; gains fertility through atmospheric deposition, biologi- Elias 2016). Indeed, more than half of all the Nitisols of cal fixation and the supply of fresh organic matter and tropical Africa are found in the Ethiopian highlands fol- nutrients to the soils (Smaling and Braun 1996; Elias et al. lowed by Kenya, Congo and Cameroon (Stocking 1988; 1998). As population increases, fallow periods are either FAO 2001). Different reports provide different area esti - shortened or abandoned altogether resulting in continu- mates of Nitisols in the Ethiopian highlands (FAO 1984; ous cultivation of the land. In some parts of the Ethiopian Zewdie 2013). The most recent survey puts the extent of highlands, steep slopes with gradients as steep as 50% Nitisols to cover about one million hectares that account are cultivated without installing adequate conservation for 31% of the agricultural lands in the Ethiopian high- measures (Assen and Tegene 2008). Often, resource-poor lands (Elias 2016). The soils are particularly extensive in farmers have a short time horizon, i.e., they are primar- the south-western and north-central highlands repre- ily concerned with the crop and animal production of the senting 64 and 25% of the agricultural landmass, respec- forthcoming season than the long-term productivity of tively (Fig.  1). Nitisols are among the most productive the soil. Longer-term processes that adversely affect agri - agricultural soils along with Vertisols, Luvisols, and cultural sustainability such as depletion of soil organic Planosols (Stocking 1988). They support the bulk of the matter and nutrient stocks are less visible and perhaps cereal and livestock production in the Ethiopian high- less noteworthy by farmers (Hailu et al. 2015; Elias 2016). lands. More importantly, the production of coffee (Cofea As result, land degradation has become a major policy arabica), the most important export commodity in Ethi- concern in Ethiopia that is experiencing one of the high- opia, relies almost exclusively on Nitisols. In addition, the est rates of soil erosion and nutrient depletion in Africa large proportion of tea production comes from strongly (Elias et  al. 1998; Hailu et  al. 2015; Laekemariam et  al. acidic Nitisols in the western part of the country (Elias −1 2016). The rate of soil erosion losses, 130  tons  ha for 2002). cultivated fields, was estimated to be one of the high - However, soil nutrient and organic matter depletion, est in Africa (FAO 1986; Elias 2016). The depletion rate acidification and soil erosion losses as result of inap - −1 −1 of macronutrients, −122 kg N ha , −13  kg P ha and propriate land use practices have become major cause −1 −82 kg K ha , was estimated to be high (Haileslassie of concern for agricultural soils in the Ethiopian high- et  al. 2005). The field level nutrient balances on Niti - lands (Elias 2002; IFPRI 2010). In particular, due to the sols reported from southern Ethiopia (−102, −45 and land form of occurrence (high to mountains relief hills −1 −67 kg N, P and K ha ) are even more threatening (Elias with moderately steep slopes) and intensive cereal cul- 2002). tivation and cattle grazing, Nitisols have become prone Among the unsustainable land use practices farmers to degradation in spite of their high structural aggregate that fuel soil degradation include low and unbalanced stability to resist erosion (FAO 2001; Elias 2016). Land Elias Environ Syst Res (2017) 6:20 Page 3 of 15 Fig. 1 Distribution and extent of Nitisols in the Ethiopian highlands −1 fertilizer application leading to mining of soil nutrient N, 46% P O ) and 100 kg ha of urea (46% N) has been 2 5 stocks, complete removal of crop residues, and dung promoted. In actual practice, the recommended rate is burning as household energy rather than recycling applied only in some high potential highland cereal zones to augment soil fertility and intensive tilling to create such as west Gojam, central Shewa and Arsi-Bale high- −1 smooth seed bed for small cereals that predisposes the lands while the national average rate of 43  kg urea ha −1 soil to erosion (Elias 2002; Hailu et  al. 2015). In addi- and 65  kg DAP ha is at best low (Elias 2016). Since tion, research reports suggest that continued application 2015, the government of Ethiopia initiated preliminary of nitrogen and phosphorus alone would accentuate the fertilizer blend formulas in which new compound fer- uptake and deficiency of other nutrients that are not sup - tilizer (NPS: 19% N, 38% P O , 7% S) was introduced to 2 5 plied in the fertilizer. Application of N and P fertilizer replace DAP for blending with potassium (K) and some alone would particularly increase the uptake of micro- micronutrients chiefly zinc (Zn) and boron (B). This has nutrients (e.g., Zn, Bo, Mn) and eventually depletes them resulted in the formulation of two poplar blends, namely, unless included in the fertilizer scheme (FAO 2006b; Zinc blend (14% N, 23% P O , 8.2% S, and 1.2% Zn) and 2 5 Elias 2016). zinc-boron blend (14% N, 21% P O 15% K O, 6.5% S, 2 5, 2 The government of Ethiopia has initiated various inter - 1.3% Zn and 0.5% B) (Karltun et  al. 2013). Efforts are ventions to arrest soil degradation primarily mass mobi- underway to prepare regional soil fertility maps to guide lisation and participatory watershed protection and fertilizer recommendations but site, crop and soil spe- fertilizer extension. Until 2015, a blanket recommenda- cific fertilizer rate recommendations are yet to be devel - −1 tion of 150 kg DAP ha (Di-ammonium Phosphate: 18% oped. This remains crucially important to maximize crop Elias Environ Syst Res (2017) 6:20 Page 4 of 15 production while at the same time maintaining soil qual- the late Eocene to the late Oligocene period. Major parent ity (through balanced nutrition) and reversing nutrient materials include basic rocks such as alkali-olivine basalts, depletion. gabbro, amphibole mixed with more recent flood basalts A more nuanced approach should, therefore, take into and tuff. considerations of the spatial diversities in soil nutrient stocks and land use practices, which are factors driv- Climate ing crop demand for soil nutrients (Elias 2016). On Much of the Nitisol areas in the Ethiopian highlands the one hand, studies suggest that soil fertility deple- are characterized by humid to sub-humid agro-climatic tion and land use effects on soil physical and chemical conditions (Elias 2016). The main monsoon rains over characteristics vary strongly across land use type, slope much of the Ethiopian highlands are influenced by the gradients and soil types (Gebreselassie et al. 2015; Hailu Inter-Tropical Convergence Zone (ITCZ) weather sys- et  al. 2015; Laekemariam et  al. 2016). On the other tem as blown from the Atlantic Ocean. The average hand, reports suggest that land use effects vary consid - annual rainfall ranges between 1300 and 1600  mm in erably with soil types with some soils being more prone the north-central highlands that falls between June and to physical and chemical deterioration than others September months. The rainy season is much extended (USDA-NRCS 2014). For example, Gebreselassie et  al. in the south-western highlands spanning from Febru- (2015) working on Luvisols in the central highlands of ary to October with average annual rainfall in the range Ethiopia reported significantly higher mean values of of 1800–2000  mm. The mean annual air temperature in organic matter, TN and exchangeable bases in the lower much of the Ethiopian highlands is 22–25 °C (Elias 2016). slope than in the upper slopes. Information on the According to Eswaren (1988) the Ethiopian highlands are effects of land use type and slope class on the physical categorized by udic soil moisture and hyperthermic soil and chemical characteristics of Nitisol is largely lack- temperature regimes. ing for the Ethiopian highlands thus impinging up on more nuanced soil fertility management decisions. Such Farming system and land use types information is crucially important for planning soil In the intensive cereal system, five major cereals form management strategies that curb the adverse effects of the staples for the population: tef (Eragrostis tef (Zucc), inappropriate land use on soil characteristics. Hence, maize (Zea mais), wheat (Triticum aestivum), barley this study was set out to evaluate how Nitisols profiles (Hordeum vulgarae) and sorghum (Sorghum bicolor). occurring in upper and lower slope positions respond to Maize-potato rotation is the main form of crop rotation different land use types in terms of their physical and and free range grazing in crop fields after harvest is com - chemical characteristics. monly practiced. In the agroforestry based system, the fields are divided into home gardens and distant out - Soil sites and methods fields. In the home gardens, enset (Enset ventricosum or Location, landform and geology Musa ensete), coffee and shade trees (e.g., Cordia afri - The study was conducted in two districts (Jabi Tehnan and cana) and fruit trees such as avocado (Persia americana) Gera) representing the cereal and agroforestry systems and mango (Mangifera indica) are typical features with in the north-central and south-western highlands where undergrowth of root crops, tubers and species. The dis - Nitisols are most dominant (Fig. 1). The landforms in the tant out fields are planted to cereals (maize, wheat, tef ) north central highlands are characterized by the undulat- that are cultivated in rotation with legumes such as faba ing to rolling high plateaus with scattered moderate relief bean (Vicia faba), haricot bean (Phaseulus vulgaris) and hills, dissected side slopes and river gorges including the soybean (Glycinemax sp.) in certain places. Trees such popular Blue Nile gorge (Elias 2016). The landform in the as Codia africana, Milletia ferruginea, Croton macros- south-western highlands is characterized by moderate to tachyus, and various species of acacia are interspersed in high relief mountains and undulating to rolling hills. Trap the crop fields providing fresh supply of organic matter Series volcanic rocks (basalt, trachyte, ignimbrite ash in the form of leaf litter to the soil. flows, and tuff ) predominate the high plateau landscapes in the north-central highlands. Basaltic basement com- plex was overflown by lavas in the Tertiary-Quaternary Tef (Eragrostis tef ) is small cereal cultivated in Ethiopia for its grain that is volcanic rocks resulting in geologically young soils that used to make the most favorite national food—Enjera. The plant rarely known are developed over pre-weathered materials (Elias 2016). as food staple outside of Ethiopia. According to Davidson (1983), the geological materials Enset (Enset ventricosum or Musa ensete otherwise called false banana) is a plant having pseudo-stem and corm that are pulped for food and fiber that building the soil profiles in the south-western highlands provides subsistence for about 10 million people in the south-western high- are recent pyroclastic deposits over the volcanic rocks of lands of Ethiopia. Elias Environ Syst Res (2017) 6:20 Page 5 of 15 Fig. 2 Location map of the study sites showing the major land use types and study districts Soil fertility management practices are also distinctly dif- 2016), Jabi Tehnan (west Gojam) and Gera (Jimma area) ferentiated according to the farming system. In the inten- districts were selected representing the intensive cereal sive cereal system the majority of farmers apply 150  kg and agroforestry systems, respectively (Fig.  2). In each −1 −1 DAP ha and 100  kg urea ha as per the extension rec- district, a “representative” sub-watershed was selected −1 ommendation thus, supplying 73–69  kg  N-P O ha . In using the slope map that was prepared following slope 2 5 the agroforestry system, the home gardens receive the classes categorization provided in FAO (2006a). Accord- application of farm yard manure and household refuse ingly, Jimat sub-watershed in Jimat Peasant Association while the outer fields are treated with 75–50 kg DAP-urea of Jabittehnan district and Garee Weychara sub-water- −1 −1 ha , thus, supplying 37–35  kg  N-P O ha . This is sup - shed in Wanja Kersa peasant association of Gera district 2 5 −1 plemented by application of on average 1.5–2.0 ton ha of were delineated (Fig.  3). The soil-landscape map of the compost as well as systematic manuring through kraaling two districts indicate that about 80% of the Nitisols are system (Elias 2016). found within lower limits of 2–5% (gently sloping) and upper limits of 15–30% (moderately steep slope). For this Soil sampling units reason, the study delineated these two slope classes as Following the intervention sites of the project that sup- lower and upper limits for soil profile sampling. In each ported the study and using the soil landscape map (Elias slope, three sample profiles were described giving a total sample of 12 profiles (Fig.  3). In the agroforestry system, profiles were opened in the distant outfields as digging During the dry season, cattle kraals are set up in crop fields that rotate to pits inside the gardens is culturally not allowable. Table 1 new fields every two weeks thus systematically distributing animal dung over much of the cultivated outfields. provides the list of profiles, their geographic location, The Dutch project, Capacity building for scaling up of evidence based slope class and elevation. Soil profile pits were opened to best practices in Ethiopia (CASCAPE for short) has supported the study. Elias Environ Syst Res (2017) 6:20 Page 6 of 15 Fig. 3 Slope map of Jabi Tehnan district (left) and Gera district (right) showing sub-watershed and soil sampling units Table 1 Geographic location, slope class, elevation and land use types in the profiles sites Profile ID Latitude Longitude Slope (%) Altitude (m) Intensive cereal-livestock system (north-central highlands) ET_AJJIP001 10°39′33.407″N 37°19′29.398″E 2–5 2790 ET_AMAMP001 11°24′26.593″N 37°3′36.276″E 2–5 2800 ET_ASAA-P001 11°21′49.326″N 36°57′8.624″E 2–5 2446 ET_ASAA-P002 11°20′21.373″N 36°55′52.203″E 15–30 1946 ET_MTA-HBP1 15–30 2272 9°26′23.008′’N 41°42′56.008″E o o ET_GIR-GGP3 8 11′36.640″N 36 56′27.632″E 15–30 2954 Agroforestry-livestock system (south-western highlands) ET_JIMG-SLP2 2–5 1917 7º46′36.005″N 36º24′33.012″E ET_JIMG-WKP1 7º47′05.003″N 36º22′17.011″E 2–5 1932 ET_BAK-AGP3 8º59′21.779″N 37º12′21.316″E 2–5 1665 ET_JIMLS-SP2 8º11′36.640″N 36º56′27.632″E 15–30 1953 ET_JIMG-GCP2 7º43′39.994″N 36º15′09.014″E 15–30 2025 ET_ILUD-MMP1 15–30 2163 8º29′07.994″N 36º20′05.014″E Soil analytical procedures a depth of 200 cm (bedrock permitting) and the soil was A total of 53 samples were collected from 12 profiles and described according to the FAO guidelines for soil taken to the soil fertility lab of the Water Works Design description (FAO 2006a). Soil samples were taken from and Supervision Enterprise (WWDSE) in Addis Ababa, each of the identified genetic horizons for laboratory Ethiopia. The analytical methods followed the standard investigation. Elias Environ Syst Res (2017) 6:20 Page 7 of 15 Table 2 Particle size limits for  coarse, medium and  fine sodium bicarbonate extraction solution at pH 8.5 (Olsen −1 sand and silt fractions (USDA-NRCS 2014) et  al. 1954) and the amount of AP (mg  kg ) was deter- mined by spectrophotometer (Van Reeuwijk 2006). Particle size fraction Sand (0.05–2 mm) Silt (0.002–0.05 mm) −1 Exchangeable cations and CEC (cmol(+) kg ) were Coarse 0.8–0.40 0.06–0.02 determined by Ammonium Acetate method at pH 7. In 2+ 2+ Medium 0.4–0.20 0.02–0.006 the leachate, Exchangeable Ca and Mg were deter- Fine 0.2–0.06 0.006–0.002 mined using Atomic Absorption Spectrophotometer + + (AAS) and Na and K by flame photometer as outlined in Van Reeuwijk (2006). The contents of selected micro - 2+ 2+ 2+ 2+ nutrients (Fe, Mn, Zn and C u ) was determined procedures as outlined in Van Reeuwijk (2006). The per - using the di-ethylene tri-amine-penta-acetic acid (DTPA) centage of sand (0.05–2.0 mm), silt (0.002–0.05 mm) and extraction method (Tan 1996). clay (<0.002 mm) fractions of the fine earth (<2 mm) was determined using the modified sedimentation hydrometer Statistical analysis and data presentation procedure (Bouyoucos 1962). Particle grain size analysis Descriptive statistics was applied and mean values for the to separate coarse, medium and fine sand and silt frac - surface horizons of all profiles investigated were com - tions was carried out following the procedures outlined puted by means of weighted average. The presence of sig - in USDA-NRCS (2014). Particle size limits for the coarse, nificant difference in mean values between the two land medium and fine fractions are given in Table  2. This was use types and slope classes was tested using paired T test to evaluate the effect of land use and slope on particle in SPSS (Statistical Package for Social Science) software size fractions which in turn have impact on erosion and Version 23. The results of the Paired T test analysis pre - management practices to be implemented. Soil aggregate sent the weighted mean values of all profiles investigated. stability test was conducted by wet sieving method as Full profile information (analytical data) on physical and outlined in USDA-NRCS (2014). It involves abrupt sub- chemical characteristics is presented for four sample mergence of air dry aggregates in water followed by wet profiles representing the two land use types and slope sieving using 0.5 mm sieve. Figures reported are percent- classes. age of aggregates retained after wet sieving. Soil moisture contents (w/w, %) were determined by means of pressure Results and discussion membrane extractor at different pressure forces to the Soil physical characteristics as affected by land use type crushed samples (Baruah and Barthakur 1997). The field and slope class capacity (FC) was determined at 1/3 bar and the perma- The soils are clayey with clay content ranging from 51 to nent wilting point (PWP) at 15 bars for sieved and air dry 55% in the A-horizon and from 58 to 72% in the B-hori- soil samples. The plant available water content (AWC) zon (Table 3). The clay enrichment in the B-horizon is as was determined as the difference between FC (the upper result of clay migration. The silt/clay ratio ranges from limit) and PWP (the lower limit). 0.28 to 0.41 in the A-horizon and from 0.22 to 0.41 in Soil pH was determined in water (pH—H O) using a the B-horizon that were rated as high according to the 1:2.5 soil to water solution ratio with a pH meter as out- ratings of Hazelton and Murphy (2007). This suggests lined in Van Reeuwijk (2006). Organic carbon (OC) con- the presence of weatherable mineral reserve in the soil. tent of the soil was analyzed using the Walkley and Black −3 The bulk density was within 1.04–1.14  g  cm range in method (Nelson and Sommers 1982). Total nitrogen (TN) −3 the A-horizon and 1.02–1.12  g  cm in the B-horizon. was analyzed according to the Macro-Kjeldahl method These values are below the critical values for agricultural that involves digestion of the sample and a wet-oxidation −3 use (1.4 g cm ) suggested by Hillel (2004) indicating the procedure (Bremner and Mulvaney 1982). Available phos- absence of excessive compaction or restrictions for root phorus (AP) content was determined using Olsen development. Land use and slope significantly (p  <  0.05) affected In Ethiopia, the Olsen’s NaHCO method (pH 8.5) is widely used for particle size distribution and plant available water con- determining soil available P. A study on the evaluation of soil test meth- tents. The mean values of fine grained texture materi - ods for available phosphorus on 32 Ethiopian soils reported that the Olsen als including 39% fine sand, 42% fine silt and 67% clay method followed by Warren and Cooke, and Truog methods is the best of the eight chemical methods they used to assess available P (Mamo and in the agroforestry system were significantly higher Hague (1991). This was further confirmed by Mamo, Christian and Heilig- than 30% fine sand, 21% fine silt and 46% clay in the tag (2002) who found the magnitude of soil available P extraction in the cereal system (Tables  4, 5). These findings suggest that order Truog > CAL > Olsen > Bray II > Warren and Cooke. Since Troug and CAL methods are not practiced in the analytical labs in Ethiopia, the although texture is an inherent property of the soil, it Olsen, Cole, Watanabe and Dean (1954) remains the best method for avail- can be altered by land use practices over a longer period able P-extraction in Ethiopia to date. Elias Environ Syst Res (2017) 6:20 Page 8 of 15 Table 3 Particle size distribution, textural class and bulk density of Nitisol sample profiles Horizon Depth (cm) Sand (%) Silt (%) Clay (%) Silt/clay Class BD (g/cm ) Profile 1: Intensive cereal upper slope (ET_ASAAP002) Ap 0–20 30 19 51 0.28 Sandy clay 1.14 AB 20–40 26 16 58 0.27 Clay 1.07 Bt1 40–80 22 18 60 0.30 Clay 1.02 Bt2 80–200 27 11 62 0.20 Clay 1.20 Profile 2: Intensive cereal lower slope (ET_AJJIP001) Ap 0–20 14 21 63 0.35 Clay 1.12 AB 20–42 12 21 67 0.31 Clay 1.10 Bt1 42–90 12 18 70 0.26 Clay 1.10 Bt2 90–200 10 20 72 0.27 Clay 1.10 Profile 3: Agroforestry upper slope (ET_JIMLS-SP2) Ah 0–12 23 23 55 0.41 Clay 1.14 BA 12–30 13 23 63 0.36 Clay 1.12 Bt1 30–0 12 26 61 0.43 Clay 1.12 Bt2 90–145 12 29 60 0.48 Clay 1.04 Bt3 145–200 12 27 62 0.43 Clay 1.06 Profile 4: Agroforestry lower slope (ET_JIM-G-SLP2 Ap 0–10 17 37 56 0.33 Clay 1.04 AB 10–30 14 22 64 0.15 Clay 1.02 Bt1 30–60 13 21 66 0.32 Clay 1.04 Bt2 60–105 11 22 63 0.42 Clay 1.07 Bt3 105–180 8 27 66 0.41 Clay 1.04 BD bulk density of time (Schaetzl and Anderson 2005). Slope effect was different between land use types (Table  7). This indicates also significant for particle size distribution. The mean that Nitisols have little water dispersible aggregates and values of fine sand (39%), fine silt (30%) and clay (63%) in hence they are fairly resistant to erosion. This is part the lower slope were significantly (p < 0.05) higher than of the reason why the Nitisols remained deep and pro- mean values in the upper slope—17% fine sand, 14% fine ductive in spite of centuries of intensive cultivation and silt and 51% clay in the upper slope (Table  6). The find - severe erosion hazards in the Ethiopian highlands (Elias ings suggest residual accumulation of coarser particles 2016). and removal of finer particles from in the upper slopes The water content of the soil at FC (1/3 bar) and PWP by runoff water and its deposition in the lower slopes. (15  bar) were 35 and 23% in the cereal system and 37 The result is in agreement with the findings of Gebrese - and 24% in the agroforestry system (Table  5). According lassie et  al. (2015) and Gebrekidan and Negassa (2006) to the rating of Hazelton and Murphy (2007), the water that reported increasing trends of coarse fractions with content at FC and PWP were rated as high while AWC increasing slope and increasing clay fractions with was in the medium to high range. The generally favour - decreasing slope gradients. able water holding capacity of the soil can be attributed Soil structural aggregate stability has a key role in to high clay content, well-developed soil structural aggre- the functioning of soil such as water retention, aera- gates and reasonably good organic matter contents of the tion, infiltration and therefore resistance to erosion soils. The result is in agreement with another report from (Abrishamkesh et al. 2010; USDA-NRCS 2014). The man Welega, western Ethiopia that found higher water hold- values of water stable aggregate (WSA), the proportion ing capacity for soils with higher clay content (Chimdi of structural aggregates retained after wet sieving in et  al. 2012). On the other hand, the mean AWC in the 0.5  mm sieve, were 79 and 87% for the intensive cereal agroforestry system (135 mm/m) was significantly higher and agroforestry systems, respectively (Table 5). Accord- than that in the cereal system (112  mm/m) suggesting ing to the ratings of Hazelton and Murphy (2007), the differences in particle grain size distribution and organic WSA was rated as very high and were not significantly matter content. Elias Environ Syst Res (2017) 6:20 Page 9 of 15 Table 4 Grain size fractionation of sand (>0.05 mm) and silt (0.05–0.002 mm) particles (%) Horizon Depth (cm) CS MS FS CSi MSi FSi Profile 1: Intensive cereal upper slope (ET_ASAAP002) Ap 0–20 62 20 18 52 27 21 AB 20–40 64 15 21 66 20 14 Bt1 40–80 62 22 16 45 20 35 Bt2 80–200 58 21 21 56 27 17 Profile 2: Intensive cereal lower slope (ET_AJJIP001) Ap 0–20 13 13 64 39 18 43 AB 20–42 12 22 66 20 25 55 Bt1 42–90 18 20 62 28 15 55 Bt2 90–200 16 22 62 13 24 63 Profile 3: Agroforestry upper slope (ET_JIMLS-SP2) Ah 0–12 45 21 34 55 25 25 BA 12–30 50 18 32 68 23 11 Bt1 30–90 48 20 32 51 34 15 Bt2 90–145 42 35 23 30 42 28 Bt3 145–200 45 27 28 44 36 20 Profile 4: Agroforestry lower slope (ET_JIM-G-SLP2) Ap 0–10 12 23 65 20 14 66 AB 10–30 10 28 62 39 19 42 Bt1 30–60 7 30 63 29 23 57 Bt2 60–105 17 25 63 29 20 51 Bt3 105–180 15 30 55 28 24 48 CS coarse sand, MS medium sand, FS fine sand; CSi coarse silt, MS medium silt, FSi fine silt Soil chemical characteristics as affected by land use The mean OC content was 2.0 and 2.1% for the inten - and slope sive cereal and agroforestry systems (Table  10). Based Tables 8 and 9 summarize important chemical character- on the ratings of Landon (1991), the OC of the soil istics of the sample profiles of Nitisols while mean values was rated very low showing no significant difference as affected by land use type and slope class are presented between the land use types. On the other hand, slope in Tables  10 and 11. The mean pH values were 5.29 and effect was significant (p  <  0.05) with higher mean val - 6.12 for the cereal and agroforestry systems (Table  8) ues (2.5% OC) in the lower slope compared to 1.5% which are statistically significantly (p  <  0.05) different. in the upper slope (Table  11). This is attributed to the Based on the ratings of Hazelton and Murphy (2007), the movement of humus particles down slope with runoff soil pH is rated as strongly acidic and moderately acidic water. The finding is in agreement with Gebreselassie respectively. The strongly acidic soil reaction in the cereal et al. (2015) that reported increasing OC contents with system was attributed to intense leaching of bases and decreasing slope. continued application of DAP and urea fertilizers. The The mean TN values, 0.15 and 0.22% for the inten - base saturation 62 and 77% for the cereal and agrofor - sive cereal and agroforestry systems, were rated low estry systems that are significantly (p  <  0.05) different based on the ratings of Landon (1991) and significantly (Table  10). The implication is that there is more intense (p  <  0.05) different between the two land use types. leaching of basic cations in the cereal system resulting in Higher TN content in the agroforestry system was due higher exchangeable acidity. In addition, the rate of fer- to crop residues addition and leaf litter accumulation tilizer application in the cereal system (100  kg urea and from land use practices that added to N-mineraliza- −1 150  kg DAP ha ) was double the rate applied in the tion. This is further elaborated by significantly lower −1 agroforestry system (i.e., 50 kg DAP and 75 kg urea ha ). C/N ratios with mean value of 10 in the agroforestry Previous research findings suggest that continuous appli - system compared to 18 in the intensive cereal system cation ammonia fertilizers such as DAP and urea can (Table  10). Although rate of decomposition was not contribute to increased exchangeable acidity of the soil measured in this study, the significantly higher C/N (Smaling and Braun 1996; Elias et al. 1998; Elias 2016). ratios are indicative of somewhat depressed microbial Elias Environ Syst Res (2017) 6:20 Page 10 of 15 Table 5 Structural aggregate stability and water holding capacity of Nitisol sample profiles Horizon Depth (cm) Water stable aggregates Water holding capacity (%) (%) −1 FC (1/3 bar) PWP (15 bar) AWC (mm m ) Profile 1: Intensive cereal upper slope (ET_ASAAP002) Ap 0–20 63 34 22 120 AB 20–40 70 35 23 120 Bt1 40–80 79 38 26 120 Bt2 80–200 76 40 28 120 Profile 2: Intensive cereal lower slope (ET_AJJIP001) Ap 0–20 85 38 26 120 AB 20–42 88 42 29 130 Bt1 42–90 89 43 30 130 Bt2 90–200 91 46 31 150 Profile 3: Agroforestry upper slope (ET_JIMLS-SP2) Ah 0–12 78 39 25 140 BA 12–30 75 37 23 140 Bt1 30–90 74 38 24 140 Bt2 90–145 69 36 22 140 Bt3 145–200 70 38 23 150 Profile 4: Agroforestry lower slope (ET_JIM-G-SLP2 Ap 0–10 91 40 23 170 AB 10–30 88 47 32 150 Bt1 30–60 93 47 31 160 Bt2 60–105 93 48 31 170 Bt3 105–180 94 49 26 230 Table 6 Mean values of physical and chemical characteristics of Nitisol (0–20 cm) as affected by slope class Soil properties Upper slope (15–30%) Lower slope (2–5%) T value Sign. Sand (%) 27 12 4.829 0.017 Silt (%) 22 25 −0.441 0.689 Clay (%) 51 63 −1.604 0.027 −3 Bulk density (g cm ) 1.2 1.1 1.787 0.172 Particle size fractions (%) Coarse sand 49 15 3.141 0.042 Medium sand 34 33 0.097 0.929 Fine sand 17 52 −4.447 0.041 Coarse silt 54 41 1.065 0.365 Medium silt 32 21 1.392 0.258 Fine silt 14 38 −2.637 0.078 Water stable aggregates 80 82 −0.935 0.419 Water holding capacity w/w, %) FC (1/3 bar) 35 37 −1.095 0.353 PWP (33 bar) 23 24 −0.662 0.555 −1 AWC (mm m ) 120 127 −1.567 0.215 decomposition of organic matter and N-mineraliza- remains subject for future research. Slope effect of TN tion in the cereal system. Further, the land use system was also significant (p < 0.05) with higher mean values might be adversely affecting soil microorganisms which in the lower slope (0.22%) compared to 0.13% in the Elias Environ Syst Res (2017) 6:20 Page 11 of 15 Table 7 Mean values of physical and chemical characteristics of Nitisols (0–20 cm) as affected by land use Soil property Intensive cereal system Agroforestry based system T value Sign. Sand (%) 28 15 3.677 0.032 Silt (%) 26 18 −2.320 0.103 Clay (%) 46 67 −5.536 0.012 −3 Bulk density (g cm ) 1.2 1.1 1.163 0.329 Particle size fractions (%) Coarse sand 43 19 6.453 0.008 Medium sand 41 16 4.494 0.021 Fine sand 30 39 −3.307 0.045 Coarse silt 59 30 7.769 0.004 Medium silt 38 17 3.859 0.031 Fine silt 21 42 −3.23 0.045 Water stable aggregates 79 87 −3.068 0.055 Water holding capacity w/w, %): FC (1/3 bar) 35 37 −1.424 0.250 PWP (33 bar) 23 24 −0.132 0.903 AWC (mm/m) 112 135 −9.000 0.003 Table 8 Selected chemical characteristics of Nitisol profiles by land use type and slope −1 Horizon Depth (cm)PH H O OC (%) TN (%) C/N CEC and exchangeable bases (cmol(+) kg ) CEC Ca Mg Na K TEB PBS Profile 1: Intensive cereal upper slope (ET_ASAA-P002) Ap 0–20 4.8 2.1 0.16 13 44 15 4 0.1 1.4 20 43 AB 20–40 5.1 1.7 0.10 17 32 14 3 0.1 1.2 18 53 Bt1 40–80 5.5 1.0 0.05 20 30 13 2 0.1 1.3 16 50 Bt2 80–200 5.7 1.0 0.06 17 30 14 4 0.2 1.2 19 60 Profile 2: Intensive cereal lower slope (ET_AJJI-P001) Ap 0–20 4.7 3.6 0.20 18 42 15 7 0.4 1.2 22 52 AB 20–42 4.9 2.0 0.12 17 49 20 7 0.4 1.1 27 55 Bt1 42–90 4.5 1.1 0.06 18 48 20 6 0.5 1.4 26 54 Bt2 90–200 4.9 1.1 0.07 15 45 17 5 0.4 1.3 22 49 Profile 3: Agroforestry upper slope (ET_JIMLS-SP2) Ah 0–12 6.2 2.5 0.25 10 37 13 14 0.2 2.2 29 78 BA 12–30 5.5 1.3 0.12 11 41 18 10 0.6 2.0 29 70 Bt1 30–90 5.5 0.9 0.09 10 35 14 10 0.9 2.0 25 71 Bt2 90–145 5.3 0.6 0.06 10 32 14 8 0.2 2.1 23 72 Bt3 145–200 5.8 0.4 0.04 10 30 12 11 0.2 2.0 18 77 Profile 4: Agroforestry lower slope (ET_JIM-G-SLP2) Ap 0–10 5.5 3.6 0.33 11 30 11 8 0.2 3.0 21 70 AB 10–30 5.9 1.9 0.13 14 28 13 8 0.1 2.0 22 79 Bt1 30–60 5.6 1.5 0.13 12 27 12 9 0.1 2.2 22 81 Bt2 60–105 5.6 1.1 0.10 11 30 12 10 0.1 2.4 23 77 Bt3 105–180 5.5 0.4 0.03 12 30 14 8 0.1 2.2 23 76 TEB total exchangeable bases, PBS percent base saturation −1 upper slope (Table  11). Similar results are reported by The mean AP content, 10 and 8  mg  kg for the cereal Gebreselassie et  al. (2015) who found increasing TN and agroforestry systems, were rated as low based on levels with decreasing slope. the ratings of Hazelton and Murphy (2007). Although Elias Environ Syst Res (2017) 6:20 Page 12 of 15 −1 Table 9 Available phosphorus and micronutrient contents (mg kg ) of the surface horizons in the Nitisol profiles Profile ID Land use Slope AP Fe Mn Zn Cu ET_ASAA-P002 Cereal 15–30 8 29 63 3 2 ET_AJJI-P001 Cereal 2–5 16 32 69 2 2 ET_JIMLS-SP2 Agroforestry 15–30 9 66 94 13 3 ET_JIM-G-SLP2 Agroforestry 2–5 8 60 98 10 2 Table 10 Mean values of selected chemical characteristics of Nitisols (0–20 cm) as affected by land use Soil property Intensive cereal system Agroforestry based system T value Sign pH–H O 5.29 6.12 −6.935 0.006 OC (%) 2.00 2.12 −0.620 0.579 Tot. N (%) 0.15 0.22 −4.217 0.024 C/N 18 10 2.600 0.080 −1 AP (mg kg ) 10.0 8 0.504 0.649 −1 CEC and basic cations (cmol(+) kg ): CEC 40 44 1.800 0.170 Ca 14 16 −1.507 0.229 Mg 6 15 −10.832 0.002 Na 0.02 0.14 0.522 0.638 K 1.60 3.0 −3.705 0.024 PBS (%) 51 75 −6.937 0.006 −1 Micronutrients (mg kg ): Fe 37 97 −8.895 0.003 Mn 39 68 −9.731 0.002 Zn 3 13 −8.278 0.004 Cu 2 3 −1.732 0.182 Table 11 Mean values of  selected chemical characteristics some profiles in the cereal system had high AP contents of Nitisols (0–20 cm) as affected by slope (Table  9), the mean values were not significantly differ - ent between the two land use types. The low levels of AP Soil properties Upper slope Lower slope T value Sign. (15–30%) (2–5%) in spite of relatively higher doses DAP application (i.e., −1 150 kg ha ) in the cereal system suggests the unavailabil- pH–H O 5.85 5.67 0.835 0.465 ity of the applied phosphate in the soil solution. This was OC (%) 1.50 2.52 −12.000 0.000 attributed to increased exchangeable acidity and higher Tot. N (%) 0.13 0.22 −4.869 0.012 P-sorption capacity of the strongly acidic soils under the C/N 8 15 −25.000 0.000 cereal system. Literature indicates the applied phosphate is −1 AP (mg kg ) 10.0 17.0 −5.085 0.015 fixed by iron and aluminum compounds (i.e., sesquioxides) −1 CEC and basic cations (cmol(+) kg ): and hence, rendered unavailable in the soil solution in low CEC 43.0 42.0 0.324 0.767 pH soils (Schaetzl and Anderson 2005; Hillel 2004). On the Ca 16.0 14.0 1.842 0.163 other hand, AP contents were significantly (p < 0.05) differ Mg 9.0 8.0 5.196 0.14 ent between the two slope classes with higher mean values Na 0.04 0.06 −0.16 0.923 −1 −1 (17 mg kg ) in the lower slope compared to 10 mg kg in K 1.2 1.4 −1.092 0.355 the upper. The conventional practice of farmers is to apply PBS (%) 62.0 58.0 1.960 0.145 DAP at planting (i.e., basal application) when the monsoon −1 Micronutrients (mg kg ): rains are at their peak that results in the runoff removal of Fe 61.0 68.0 −0.733 0.516 some of the applied fertilizer from the upper slopes that Mn 46.0 55.0 −1.741 0.180 are deposited in the lower slopes. Zn 9.0 9.0 1.000 0.391 2+ On the other hand, the CEC, exchangeable bases (Ca , Cu 3.0 2.0 0.775 0.95 2+ + Mg, K ) and PBS of the soil were rated high based on the Elias Environ Syst Res (2017) 6:20 Page 13 of 15 ratings of Landon (1991) while N a appeared only in trace plant available water contents (AWC), soil pH and OC, amount. The paired T-test showed no significant difference TN, AP exchangeable basses and some micronutrients. 2+ between land use type and slope classes except for M g , The land use practices in the intensive cereal system was + 2+ −1 + K and PBS. Mean values of M g (15  cmol(+) kg), K found to be adversely affecting important soil physical −1 (3 cmol(+) kg ) and PBS (75%) in the agroforestry system and chemical characteristics as compared to the agro- were significantly higher than those in the cereal system (6 forestry system. These include alteration of particle size −1 2+ + and 1.6  cmol(+) kg of Mg and K and 51% PBS). The distribution, strongly acidic soil reaction, organic matter PBS was in the medium to high range (43–60%) in the cereal depletion, multiple nutrient deficiencies (N, P, K and Zn) system while it was high to very high (70–81%) in the agro- and low plant available water content. Among the inap- forestry system (Table 8). The generally high base saturation propriate land use practices include repeated cultivation of the soil was consistent with high contents of exchange- to create fine seedbed that predisposes the soil to ero - 2+ 2+ able bases (chiefly Ca and Mg ) but not consistent with sion, unbalanced fertilizer application, rotation of maize generally acidic soil reaction (pH 5.5–6.2) that needs some with potato that are depleting some nutrient stocks (e., K explanation. First, the soils in the Ethiopian highlands have and Zn), and removal of crop residues from fields. As can developed on recent Trapean lava flows that have high base be seen from the significantly lower PBS in the cereal sys - status (Mohr 1971). Secondly, according to Buol et al. (2011) tem, leaching of basic cations was intense that resulted in the volcanic parent materials such as rhyolites, granite, tra- increased levels of exchangeable acidity. In addition, con- chytes, ignimbrites, andesites and some acidic basalts that tinued use of DAP and urea seems to have contributed dominate the Ethiopian produce inherently acidic clays. to increased exchangeable acidity as well as accentuating Thirdly, the humid climatic conditions might have resulted the uptake and deficiency of other nutrients such as K in increased microbial oxidation to produced organic and Zn that are not supplied in the fertilizer application. acids, which provide H to the soil that can also contribute Slope position of the profiles also had significant effect towards low soil pH (Schaetzl and Anderson 2005). on soil characteristics with significantly higher propor - 2+ 2+ 2+ 2+ The mean values for Fe, Mn, Zn and Cu were tions of coarse textured particles that were low in OC, AP −1 respectively 37, 39, 3 and 2  mg  kg in the cereal system and TN contents in the upper slope compared to lower −1 while it was 97, 68, 13 and 3  mg  kg in the agroforestry slopes. Organic matter and nutrient contents decreased system (Table  9). According to the ratings of Havlin et al. with increasing slope gradient particularly in the cereal (1999), the micronutrient contents were rated as high to system indicating the effect of erosional losses of fine very high except for Z n that was low to medium. The high particles. levels of micronutrients is consistent with the low pH of The data, therefore, provides useful information for 2+ the soil and the low Zn contents are in agreement with planning soil management strategies that can address previous report that indicated widespread Zn deficiency in adverse effects of land use on soil characteristics. First the Nitisol areas of the Ethiopian highlands (Dibabe et al. and foremost, application of more balanced blend ferti- 2007). According to FAO (2006b), low soil pH induces lizer that contains N, P, K and Zn combined with liming increase in micronutrient contents that may eventually to raise the soil pH remains crucially important. In this lead to root toxicity unless soil pH is corrected through connection, research needs to generate NPS and Zn-B liming. The paired T-test showed significant (p < 0.05) dif - blend fertilizer applications rates for different crops, soil 2+ 2+ 2+ ference between land use types for Fe, Mn , and Zn types and land use systems. Increasing the rate of fer- 2+ but slope effect was nonsignificant. The mean value of Fe tilizer application is particularly crucial in the agrofor- −1 2+ −1 2+ −1 (97 mg kg), Mn (68 mg kg ) and Zn (13 mg kg ) in estry based system where current rates of fertilizer use the agroforestry system were significantly higher than 37, are far too low. However, given the very high levels of −1 2+ 2+, 2+ 39 and 3  mg  kg of Fe, Mn and Zn in the cereal Zn in the soil, Zn-blend should not be extended to farm- system (Table  10). According to Mohr (1971) and David- ers in the agroforestry system. Secondly, organic matter son (1983), the soil parent materials in the agroforestry management including restitution of crop residues and system are dominated by basic rocks such as alkali-olivine recycling of farm yard manure is fundamental in order basalts, amphibole and mica that are rich in ferromanga- to reverse the OC depletion and increase water hold- 2+ nese minerals thus explaining the exceptionally high F e ing capacity of the soil. Third, although Nitisols have 2+ and Mn contents in these sites. high structural aggregate stability that are fairly resist- ant to erosion, their landform of occurrence (i.e., high Conclusion to mountainous relief hills with steep slopes) makes The study showed that land use practices and slope class the soils susceptible to degradation by water erosion. significantly affects important soil physical and chemical This calls for the implementation of integrated soil and characteristics. These include particle size distribution, water conservation measures that combine physical, Elias Environ Syst Res (2017) 6:20 Page 14 of 15 Received: 13 January 2017 Accepted: 8 August 2017 biological and agronomic measures mainly in the cereal system. In addition, soil textural fractionation analysis indicates that repeated tillage practice is found to pre- dispose the soil to erosion by adversely affecting the soil textural fractions. Therefore, minimum tillage combined References with legume rotation (maize-tef-bean) observed in some Abrishamkesh S, Gorji M, Asadi H (2010) Long-term effects of land use on soil aggregate stability. Int Agrophys 25:103–108 parts of west Gojam (e.g., South Achefer and Bure) need Assen M, Amd Tegene B (2008) Characteristics and classification of the soils to be widely disseminated among farmers in the cereal- of the plateau of Siemen Mountains National Park. SINET Ethiopia J Sci livestock highlands. 31(2):89–102 Baruah TC, Barthakur HP (1997) A textbook of soils analysis. Vikas Publishing House, New Delhi Bouyoucos GJ (1962) Hydrometer method improvement for making particle Abbreviations −1 size analysis of soils. Agronomy 5:179–186 AP: available phosphorus (mg kg ); AWC: available water content; BD: bulk 3 Bremner JM, Mulvaney CS (1982) Total nitrogen. In: Page AL, Miller RH, Keeney density (dgcm ); C/N: carbon to nitrogen ratio; Ca/Mg: calcium to magnesium −1 −1 DR (ed) Methods of soil analysis II. Chemical and microbiological proper- ratio; CEC: cation exchange capacity (cmol(+) kg ); Cu: copper (mg kg ); ties. American Society of Agronomy, Soil Science Society of America DAP: di-ammonium phosphate (18% N, 46% P O ); FC: field capacity; ITCZ: 2 5 −1 Buol SW, Southard RJ, Graham RC, McDaniel PA (2011). Soil genesis and clas- Inter Tropical Convergence Zone; K: Potassium (cmol(+) kg ); Mg: Magne- −1 −1 −1 sification, 6th edn. Wiley-Blackwell, London sium (cmol(+) kg ); Mn: Manganese (mg kg ); Na: Sodium (cmol(+) kg ); Chimdi A, Gebrekidan H, Kibret K, Tadesse A (2012) Status of selected physico- PBS: percent base saturation; SC: sandy clay; TN: total nitrogen (%); PWP: −1 chemical properties of soils under different land use systems of Western permanent wilting point; WSA: water stable aggregates; Zn: zinc (mg kg ). Oromia, Ethiopia. J Biodivers Environ Sci 2(3):57–71 Davidson A (1983) The Omo river project: reconnaissance geology and geo- Author’s information chemistry of parts of Ilubabor, Kafa, Gamo Gofa, and Sidamo. Ethiop Instit The author is a Ph.D. working in the area of Soil Science and environment Geol Surv 2:1–89 having 20 years of post-Ph.D. research, teaching and development work. Dibabe A, Bekele T, Assen Y (2007) The status of micronutrients in Nitisols, Currently, he holds associate Professor’s position with College of Natural and Vertisols, Cambisols and Fluvsisols in major maize, wheat, tef and citrus Computational Science of Addis Ababa University. Over the past years, he growing areas of Ethiopia. Ethiopian Agricultural Research Organization has been working on soil survey, characterization and mapping work with (EARO) Research Report, Addis Ababa scientists from the Wageningen University and Research Centre and the Elias E (2002) Farmers perceptions of soil fertility change and management. In: International Soil Reference and Information Centre (ISRIC), the Netherlands. SOS-Sahel and institute for sustainable development, Addis Ababa Some of his work has recently been published in a book entitled, “Soils of the Elias E (2016) Soils of the Ethiopian highlands: geomorphology and properties. Ethiopian Highlands: Geomorphology and Properties”—ISBN: 978-99944- ALTERA Wageningen University Research Centre, The Netherlands. ISBN: 952-6-9. In addition, the author published a number of peer reviewed journal 978-99944-952-6-9 articles and book chapters previously. Elias E, Morse S, Belshaw DG (1998) Nitrogen and phosphorus balances of Kindo Koisha farms in southern Ethiopia. Agric Ecosyst Environ 71(1):93–113 Eswaren H (1988) Taxonomy and management related properties of the red Acknowledgements soils of Africa. In: Nyamapfene K, Hussein J, Asumadu K (eds) The red soils The author acknowledges the technical support of CASCAPE field staff in the of eastern and southern Africa. Proceedings of an international sympo- study sites. These technical assistance do not qualify for co-authorship since sium, Harare, pp 1–23 data accrual, analysis, interpretation and write was done solely by the author. FAO (1984) Geomorphology and soils of Ethiopia. In: Assistance to land use planning and provisional soil association map of Ethiopia. Field document Competing interests AG DP/ETH/78/003. Food and Agriculture Organization of the UN, Rome The authors declares that there is no financial or non-financial competing FAO (1986) The Ethiopian highlands reclamation study (EHRS). vol 1, In: Main interests. Report. Food and Agriculture Organization of the UN, Rome FAO (2001) Lecture notes on the major soils of the world. In: ISRIC-ITC-Catholic Availability of data and materials University of Leuven World soil resources Report No 94. Food and Agri- I declare that the data and materials presented in this manuscript can be culture Organization, Rome made publically available by Springer Open as per the editorial policy. FAO (2006a) Guideline for soil description. 4th edn, Food and Agriculture Organization of the UN, Rome Consent for publication FAO (2006b) Plant nutrition for food security: a guide for integrated nutrient The manuscript does not contain no data or information from any person or management. In: FAO fertilizer and plant nutrition, vol 16. Food and individual apart from his own field investigation. All data and information are Agriculture Organization of the UN, Rome generated and synthesized by the author himself. Gebrekidan H, Negassa W (2006) Impact of land use and management prac- tices on chemical properties some soils of Bako area, western Ethiopia. Ethics approval and consent to participate Ethiop J Nat Res 8(2):177–197 Not applicable to this manuscript submission. Gebreselassie Y, Anemut F, Addis S (2015) The effects of land use types, man- agement practices and slope classes on selected soil physico-chemical Funding properties in Zikre watershed, North-Western Ethiopia. Environ Syst Res This research was conducted as part of the action research and capacity 4(3):1–7. doi:10.1186/s40068-015-0027-0 building project entitled, “Capacity building for Scaling up of Evidence based Haileslassie A, Priess J, Veldkamp E, Teketay D, Lesschen JP (2005) Assessment best Practices for increased Agricultural Production in Ethiopia (CASCAPE)” of soil nutrient depletion and its spatial variability on smallholders’ mixed with kind financial assistance from the Ministry of Foreign Affairs of the Dutch farming systems in Ethiopia using partial versus full nutrient balances. Government through its Embassy in Addis Ababa. Agric Ecosyst Environ 108:1–16 Hailu H, Mamo T, Keskinen R, Karltun E, Gebrekidan H, Bekele T (2015) Soil Publisher’s Note fertility status and wheat nutrient content in Vertisol cropping systems of Springer Nature remains neutral with regard to jurisdictional claims in pub- central highlands of Ethiopia. Agric Food Secur 4(19):1–10. doi:10.1186/ lished maps and institutional affiliations. s40066-015-0038-0 Elias Environ Syst Res (2017) 6:20 Page 15 of 15 Havlin JL, Beaton JD, Tisdale SL, Nelson WL (1999) Soil fertility and fertilizers. Mohr AP (1971) The geology of Ethiopia. Haile Selassie I University Press, Addis Prentice Hall, New Jersey Ababa Hazelton P and Murphy B (2007) Interpreting soil test results: what do all those Nelson DW and Sommers LE (1982) Total carbon, organic carbon and organic numbers mean? CSIRO. Department of Natural Resources matter. In: Page AL (ed) Methods of soil analysis, Part 2: chemical and Hillel D (2004) Introduction to environmental soil physics. Elsevier Academic microbiological properties. Agronomy, Madison, pp 539–579 Press, Amsterdam Olsen SR, Cole CV, Watanabe FS, Dean LA (1954) Estimation of available phos- IFPRI (2010) Fertilizer and soil fertility potentials in Ethiopia. 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III, Evalua- Van Reeuwijk LP (2006) Procedures for soil analysis, 6th edn. International soil tion of soil test methods for available phosphorus. Trop Agric 68:51–56 reference and information centre (ISRIC), Wageningen, The Netherlands Mamo T, Christian R, Heiligtag Burkhard (2002) Phosphorus availability studies Zewdie E (2013) Properties of major agricultural soils of Ethiopia. Lambert on ten Ethiopian Vertisols. J Agric Rural Dev Trop Subtrop 103(2):177–183 Academic Publishing, Germany http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Environmental Systems Research Springer Journals

Characteristics of Nitisol profiles as affected by land use type and slope class in some Ethiopian highlands

Environmental Systems Research , Volume 6 (1) – Aug 23, 2017

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Copyright © 2017 by The Author(s)
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Environment; Monitoring/Environmental Analysis
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2193-2697
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10.1186/s40068-017-0097-2
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Abstract

Background: The success of soil management depends on understanding of how soils respond to agricultural land use practices over time. Nitisols are among the most extensive agricultural soils in the Ethiopian highlands but soil degradation threatens their productive capacity. In this study, the effects of two land use systems, intensive cereal and agroforestry systems, and slope class on physical and chemical characteristics of some Nitisol profiles were investigated. In total 12 sample profiles were described and soil samples were collected from each of the identified master horizon. Soil physical characteristics evaluated were particle size distribution, structural aggregate stability, water holding capacity and bulk density. Chemical characteristics determined were exchangeable bases and cation exchange capacity, soil pH and the contents of organic carbon (OC), total nitrogen ( TN), available phosphorus (AP) and some micronutrients. Results: Among the physical characteristics, land use and slope significantly (p < 0.05) affected particle size distribu- tion and plant available water content. The mean sand (28%) and silt (26%) particles in the intensive cereal system were significantly (p < 0.05) higher compared to 15% sand and 18% silt in the agroforestry system. Conversely, the mean values of fine grained texture materials including 39% fine sand, 42% fine silt and 67% clay in the agroforestry system were significantly higher than 30% fine sand, 21% fine silt and 46% clay in the cereal system. Similarly, the lower slope had significantly (p < 0.05) higher fin texture materials (39% fine sand, 30% fine silt, and 63%) clay) com- pared to 17% fine sand, 14% fine silt and 51% clay fractions in the upper slope. The proportion of water stable aggre - gate ( WSA) were highlight (63–94%) and there was no significant difference between land types and slope classes. Following from high structural aggregate stability, the soils have high water holding capacity that ranged from 22 to −1 32% at PWP to 34–49% at FC while plant available water content (AWC) was in the 120–230 mm m range. Consider- ing the chemical characteristics, land use significantly affected soil pH, total nitrogen ( TN), exchangeable magnesium 2+ + 2+ 2+ (Mg ), potassium (K ), percent base saturation (PBS), and available micro nutrients—iron (Fe ), manganese (Mn ) 2+ and zinc (Zn ). The mean pH value (5.29) in the intensive cereal system strongly acidic while the pH value for the agroforestry system (6.12) was taken moderately acidic. The mean OC content was 2.0 and 2.1% for the intensive cereal and agroforestry systems that were rated very low. The mean TN values were 0.15 and 0.22% for intensive cereal −1 and agroforestry systems that were taken as low to very low. Similarly the mean values for AP were 8 and 10 mg kg 2+ 2+ for cereal and agroforestry systems that were rated low. On the other hand, the CEC, exchangeable bases ( Ca, Mg , + + K ) and PBS of the soil were rated high while Na appeared only in trace amount, and there was no significant differ - 2+ + 2+ + ence between land use type and slope classes except for Mg , K and PBS. Mean values of Mg and K (15 and 3 −1 cmol(+) kg ) and PBS (75%) in the agroforestry system were significantly higher than those in the cereal system (6 −1 2+ + and 1.6 cmol(+) kg of Mg and K and 51% PBS). Among micronutrients, land use significantly (p < 0.05) affected *Correspondence: Eyasu.elias@aau.edu.et; eyuelias@gmail.com Centre for Environmental Science, College of Natural and Computational Sciences, Addis Ababa University, Addis Ababa, Ethiopia © The Author(s) 2017. 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. Elias Environ Syst Res (2017) 6:20 Page 2 of 15 2+ 2+ + 2+ −1 2+ −1 available Fe, Mn and Zn . The mean values of Fe (97 mg kg ) and Mn (68 mg kg ) in the agroforestry −1 system were taken as excessively high while they were moderately sufficient (37, 39 mg kg , respectively) in the cereal system. Slope effects were significant for OC, TN and AP having higher mean values (2.5% OC, 0.22% TN and −1 −1 17 mg kg AP) in the lower slope than in the upper slope (1.5% OC, 0.13% TN and 8 mg kg AP). Conclusion: Land use and slope had significant effect on some soil physical and chemical characteristics. The land use practices in the intensive cereal system are adversely affecting important soil characteristics as compared to the soil under the agroforestry system. These include alteration of particle size distribution, strongly acidic soil reaction, organic matter and nutrient depletion (N, P, K and Zn) and low plant available water content. Among the inappro- priate land use practices include repeated cultivation to create fine seedbed that predisposes the soil to erosion, unbalanced fertilizer application, rotation of maize with potato that are depleting soil nutrient stocks (e., K and Zn), and removal of crop residues from fields. Therefore, a more balanced fertilizer blend application that contain N, P, K and Zn combined with liming to raise soil pH, organic matter management and integrated soil water conservation are recommended. Keywords: Land use, Nitisol profiles, Physical and chemical characteristics, Slope use changes and cultivation of fields without adequate Background conservation practices, low levels of fertilizer application In Ethiopia, diversities in state factors such as topog- and failure to recycle crop residues are among the causal raphy, parent materials, climate and vegetation have factors. Traditionally, soil fertility is replenished through resulted in the development of 18 soil types of which fallow cycles of up to 20 years during which time the land Nitisols are among the most extensive soils (FAO 1984; gains fertility through atmospheric deposition, biologi- Elias 2016). Indeed, more than half of all the Nitisols of cal fixation and the supply of fresh organic matter and tropical Africa are found in the Ethiopian highlands fol- nutrients to the soils (Smaling and Braun 1996; Elias et al. lowed by Kenya, Congo and Cameroon (Stocking 1988; 1998). As population increases, fallow periods are either FAO 2001). Different reports provide different area esti - shortened or abandoned altogether resulting in continu- mates of Nitisols in the Ethiopian highlands (FAO 1984; ous cultivation of the land. In some parts of the Ethiopian Zewdie 2013). The most recent survey puts the extent of highlands, steep slopes with gradients as steep as 50% Nitisols to cover about one million hectares that account are cultivated without installing adequate conservation for 31% of the agricultural lands in the Ethiopian high- measures (Assen and Tegene 2008). Often, resource-poor lands (Elias 2016). The soils are particularly extensive in farmers have a short time horizon, i.e., they are primar- the south-western and north-central highlands repre- ily concerned with the crop and animal production of the senting 64 and 25% of the agricultural landmass, respec- forthcoming season than the long-term productivity of tively (Fig.  1). Nitisols are among the most productive the soil. Longer-term processes that adversely affect agri - agricultural soils along with Vertisols, Luvisols, and cultural sustainability such as depletion of soil organic Planosols (Stocking 1988). They support the bulk of the matter and nutrient stocks are less visible and perhaps cereal and livestock production in the Ethiopian high- less noteworthy by farmers (Hailu et al. 2015; Elias 2016). lands. More importantly, the production of coffee (Cofea As result, land degradation has become a major policy arabica), the most important export commodity in Ethi- concern in Ethiopia that is experiencing one of the high- opia, relies almost exclusively on Nitisols. In addition, the est rates of soil erosion and nutrient depletion in Africa large proportion of tea production comes from strongly (Elias et  al. 1998; Hailu et  al. 2015; Laekemariam et  al. acidic Nitisols in the western part of the country (Elias −1 2016). The rate of soil erosion losses, 130  tons  ha for 2002). cultivated fields, was estimated to be one of the high - However, soil nutrient and organic matter depletion, est in Africa (FAO 1986; Elias 2016). The depletion rate acidification and soil erosion losses as result of inap - −1 −1 of macronutrients, −122 kg N ha , −13  kg P ha and propriate land use practices have become major cause −1 −82 kg K ha , was estimated to be high (Haileslassie of concern for agricultural soils in the Ethiopian high- et  al. 2005). The field level nutrient balances on Niti - lands (Elias 2002; IFPRI 2010). In particular, due to the sols reported from southern Ethiopia (−102, −45 and land form of occurrence (high to mountains relief hills −1 −67 kg N, P and K ha ) are even more threatening (Elias with moderately steep slopes) and intensive cereal cul- 2002). tivation and cattle grazing, Nitisols have become prone Among the unsustainable land use practices farmers to degradation in spite of their high structural aggregate that fuel soil degradation include low and unbalanced stability to resist erosion (FAO 2001; Elias 2016). Land Elias Environ Syst Res (2017) 6:20 Page 3 of 15 Fig. 1 Distribution and extent of Nitisols in the Ethiopian highlands −1 fertilizer application leading to mining of soil nutrient N, 46% P O ) and 100 kg ha of urea (46% N) has been 2 5 stocks, complete removal of crop residues, and dung promoted. In actual practice, the recommended rate is burning as household energy rather than recycling applied only in some high potential highland cereal zones to augment soil fertility and intensive tilling to create such as west Gojam, central Shewa and Arsi-Bale high- −1 smooth seed bed for small cereals that predisposes the lands while the national average rate of 43  kg urea ha −1 soil to erosion (Elias 2002; Hailu et  al. 2015). In addi- and 65  kg DAP ha is at best low (Elias 2016). Since tion, research reports suggest that continued application 2015, the government of Ethiopia initiated preliminary of nitrogen and phosphorus alone would accentuate the fertilizer blend formulas in which new compound fer- uptake and deficiency of other nutrients that are not sup - tilizer (NPS: 19% N, 38% P O , 7% S) was introduced to 2 5 plied in the fertilizer. Application of N and P fertilizer replace DAP for blending with potassium (K) and some alone would particularly increase the uptake of micro- micronutrients chiefly zinc (Zn) and boron (B). This has nutrients (e.g., Zn, Bo, Mn) and eventually depletes them resulted in the formulation of two poplar blends, namely, unless included in the fertilizer scheme (FAO 2006b; Zinc blend (14% N, 23% P O , 8.2% S, and 1.2% Zn) and 2 5 Elias 2016). zinc-boron blend (14% N, 21% P O 15% K O, 6.5% S, 2 5, 2 The government of Ethiopia has initiated various inter - 1.3% Zn and 0.5% B) (Karltun et  al. 2013). Efforts are ventions to arrest soil degradation primarily mass mobi- underway to prepare regional soil fertility maps to guide lisation and participatory watershed protection and fertilizer recommendations but site, crop and soil spe- fertilizer extension. Until 2015, a blanket recommenda- cific fertilizer rate recommendations are yet to be devel - −1 tion of 150 kg DAP ha (Di-ammonium Phosphate: 18% oped. This remains crucially important to maximize crop Elias Environ Syst Res (2017) 6:20 Page 4 of 15 production while at the same time maintaining soil qual- the late Eocene to the late Oligocene period. Major parent ity (through balanced nutrition) and reversing nutrient materials include basic rocks such as alkali-olivine basalts, depletion. gabbro, amphibole mixed with more recent flood basalts A more nuanced approach should, therefore, take into and tuff. considerations of the spatial diversities in soil nutrient stocks and land use practices, which are factors driv- Climate ing crop demand for soil nutrients (Elias 2016). On Much of the Nitisol areas in the Ethiopian highlands the one hand, studies suggest that soil fertility deple- are characterized by humid to sub-humid agro-climatic tion and land use effects on soil physical and chemical conditions (Elias 2016). The main monsoon rains over characteristics vary strongly across land use type, slope much of the Ethiopian highlands are influenced by the gradients and soil types (Gebreselassie et al. 2015; Hailu Inter-Tropical Convergence Zone (ITCZ) weather sys- et  al. 2015; Laekemariam et  al. 2016). On the other tem as blown from the Atlantic Ocean. The average hand, reports suggest that land use effects vary consid - annual rainfall ranges between 1300 and 1600  mm in erably with soil types with some soils being more prone the north-central highlands that falls between June and to physical and chemical deterioration than others September months. The rainy season is much extended (USDA-NRCS 2014). For example, Gebreselassie et  al. in the south-western highlands spanning from Febru- (2015) working on Luvisols in the central highlands of ary to October with average annual rainfall in the range Ethiopia reported significantly higher mean values of of 1800–2000  mm. The mean annual air temperature in organic matter, TN and exchangeable bases in the lower much of the Ethiopian highlands is 22–25 °C (Elias 2016). slope than in the upper slopes. Information on the According to Eswaren (1988) the Ethiopian highlands are effects of land use type and slope class on the physical categorized by udic soil moisture and hyperthermic soil and chemical characteristics of Nitisol is largely lack- temperature regimes. ing for the Ethiopian highlands thus impinging up on more nuanced soil fertility management decisions. Such Farming system and land use types information is crucially important for planning soil In the intensive cereal system, five major cereals form management strategies that curb the adverse effects of the staples for the population: tef (Eragrostis tef (Zucc), inappropriate land use on soil characteristics. Hence, maize (Zea mais), wheat (Triticum aestivum), barley this study was set out to evaluate how Nitisols profiles (Hordeum vulgarae) and sorghum (Sorghum bicolor). occurring in upper and lower slope positions respond to Maize-potato rotation is the main form of crop rotation different land use types in terms of their physical and and free range grazing in crop fields after harvest is com - chemical characteristics. monly practiced. In the agroforestry based system, the fields are divided into home gardens and distant out - Soil sites and methods fields. In the home gardens, enset (Enset ventricosum or Location, landform and geology Musa ensete), coffee and shade trees (e.g., Cordia afri - The study was conducted in two districts (Jabi Tehnan and cana) and fruit trees such as avocado (Persia americana) Gera) representing the cereal and agroforestry systems and mango (Mangifera indica) are typical features with in the north-central and south-western highlands where undergrowth of root crops, tubers and species. The dis - Nitisols are most dominant (Fig. 1). The landforms in the tant out fields are planted to cereals (maize, wheat, tef ) north central highlands are characterized by the undulat- that are cultivated in rotation with legumes such as faba ing to rolling high plateaus with scattered moderate relief bean (Vicia faba), haricot bean (Phaseulus vulgaris) and hills, dissected side slopes and river gorges including the soybean (Glycinemax sp.) in certain places. Trees such popular Blue Nile gorge (Elias 2016). The landform in the as Codia africana, Milletia ferruginea, Croton macros- south-western highlands is characterized by moderate to tachyus, and various species of acacia are interspersed in high relief mountains and undulating to rolling hills. Trap the crop fields providing fresh supply of organic matter Series volcanic rocks (basalt, trachyte, ignimbrite ash in the form of leaf litter to the soil. flows, and tuff ) predominate the high plateau landscapes in the north-central highlands. Basaltic basement com- plex was overflown by lavas in the Tertiary-Quaternary Tef (Eragrostis tef ) is small cereal cultivated in Ethiopia for its grain that is volcanic rocks resulting in geologically young soils that used to make the most favorite national food—Enjera. The plant rarely known are developed over pre-weathered materials (Elias 2016). as food staple outside of Ethiopia. According to Davidson (1983), the geological materials Enset (Enset ventricosum or Musa ensete otherwise called false banana) is a plant having pseudo-stem and corm that are pulped for food and fiber that building the soil profiles in the south-western highlands provides subsistence for about 10 million people in the south-western high- are recent pyroclastic deposits over the volcanic rocks of lands of Ethiopia. Elias Environ Syst Res (2017) 6:20 Page 5 of 15 Fig. 2 Location map of the study sites showing the major land use types and study districts Soil fertility management practices are also distinctly dif- 2016), Jabi Tehnan (west Gojam) and Gera (Jimma area) ferentiated according to the farming system. In the inten- districts were selected representing the intensive cereal sive cereal system the majority of farmers apply 150  kg and agroforestry systems, respectively (Fig.  2). In each −1 −1 DAP ha and 100  kg urea ha as per the extension rec- district, a “representative” sub-watershed was selected −1 ommendation thus, supplying 73–69  kg  N-P O ha . In using the slope map that was prepared following slope 2 5 the agroforestry system, the home gardens receive the classes categorization provided in FAO (2006a). Accord- application of farm yard manure and household refuse ingly, Jimat sub-watershed in Jimat Peasant Association while the outer fields are treated with 75–50 kg DAP-urea of Jabittehnan district and Garee Weychara sub-water- −1 −1 ha , thus, supplying 37–35  kg  N-P O ha . This is sup - shed in Wanja Kersa peasant association of Gera district 2 5 −1 plemented by application of on average 1.5–2.0 ton ha of were delineated (Fig.  3). The soil-landscape map of the compost as well as systematic manuring through kraaling two districts indicate that about 80% of the Nitisols are system (Elias 2016). found within lower limits of 2–5% (gently sloping) and upper limits of 15–30% (moderately steep slope). For this Soil sampling units reason, the study delineated these two slope classes as Following the intervention sites of the project that sup- lower and upper limits for soil profile sampling. In each ported the study and using the soil landscape map (Elias slope, three sample profiles were described giving a total sample of 12 profiles (Fig.  3). In the agroforestry system, profiles were opened in the distant outfields as digging During the dry season, cattle kraals are set up in crop fields that rotate to pits inside the gardens is culturally not allowable. Table 1 new fields every two weeks thus systematically distributing animal dung over much of the cultivated outfields. provides the list of profiles, their geographic location, The Dutch project, Capacity building for scaling up of evidence based slope class and elevation. Soil profile pits were opened to best practices in Ethiopia (CASCAPE for short) has supported the study. Elias Environ Syst Res (2017) 6:20 Page 6 of 15 Fig. 3 Slope map of Jabi Tehnan district (left) and Gera district (right) showing sub-watershed and soil sampling units Table 1 Geographic location, slope class, elevation and land use types in the profiles sites Profile ID Latitude Longitude Slope (%) Altitude (m) Intensive cereal-livestock system (north-central highlands) ET_AJJIP001 10°39′33.407″N 37°19′29.398″E 2–5 2790 ET_AMAMP001 11°24′26.593″N 37°3′36.276″E 2–5 2800 ET_ASAA-P001 11°21′49.326″N 36°57′8.624″E 2–5 2446 ET_ASAA-P002 11°20′21.373″N 36°55′52.203″E 15–30 1946 ET_MTA-HBP1 15–30 2272 9°26′23.008′’N 41°42′56.008″E o o ET_GIR-GGP3 8 11′36.640″N 36 56′27.632″E 15–30 2954 Agroforestry-livestock system (south-western highlands) ET_JIMG-SLP2 2–5 1917 7º46′36.005″N 36º24′33.012″E ET_JIMG-WKP1 7º47′05.003″N 36º22′17.011″E 2–5 1932 ET_BAK-AGP3 8º59′21.779″N 37º12′21.316″E 2–5 1665 ET_JIMLS-SP2 8º11′36.640″N 36º56′27.632″E 15–30 1953 ET_JIMG-GCP2 7º43′39.994″N 36º15′09.014″E 15–30 2025 ET_ILUD-MMP1 15–30 2163 8º29′07.994″N 36º20′05.014″E Soil analytical procedures a depth of 200 cm (bedrock permitting) and the soil was A total of 53 samples were collected from 12 profiles and described according to the FAO guidelines for soil taken to the soil fertility lab of the Water Works Design description (FAO 2006a). Soil samples were taken from and Supervision Enterprise (WWDSE) in Addis Ababa, each of the identified genetic horizons for laboratory Ethiopia. The analytical methods followed the standard investigation. Elias Environ Syst Res (2017) 6:20 Page 7 of 15 Table 2 Particle size limits for  coarse, medium and  fine sodium bicarbonate extraction solution at pH 8.5 (Olsen −1 sand and silt fractions (USDA-NRCS 2014) et  al. 1954) and the amount of AP (mg  kg ) was deter- mined by spectrophotometer (Van Reeuwijk 2006). Particle size fraction Sand (0.05–2 mm) Silt (0.002–0.05 mm) −1 Exchangeable cations and CEC (cmol(+) kg ) were Coarse 0.8–0.40 0.06–0.02 determined by Ammonium Acetate method at pH 7. In 2+ 2+ Medium 0.4–0.20 0.02–0.006 the leachate, Exchangeable Ca and Mg were deter- Fine 0.2–0.06 0.006–0.002 mined using Atomic Absorption Spectrophotometer + + (AAS) and Na and K by flame photometer as outlined in Van Reeuwijk (2006). The contents of selected micro - 2+ 2+ 2+ 2+ nutrients (Fe, Mn, Zn and C u ) was determined procedures as outlined in Van Reeuwijk (2006). The per - using the di-ethylene tri-amine-penta-acetic acid (DTPA) centage of sand (0.05–2.0 mm), silt (0.002–0.05 mm) and extraction method (Tan 1996). clay (<0.002 mm) fractions of the fine earth (<2 mm) was determined using the modified sedimentation hydrometer Statistical analysis and data presentation procedure (Bouyoucos 1962). Particle grain size analysis Descriptive statistics was applied and mean values for the to separate coarse, medium and fine sand and silt frac - surface horizons of all profiles investigated were com - tions was carried out following the procedures outlined puted by means of weighted average. The presence of sig - in USDA-NRCS (2014). Particle size limits for the coarse, nificant difference in mean values between the two land medium and fine fractions are given in Table  2. This was use types and slope classes was tested using paired T test to evaluate the effect of land use and slope on particle in SPSS (Statistical Package for Social Science) software size fractions which in turn have impact on erosion and Version 23. The results of the Paired T test analysis pre - management practices to be implemented. Soil aggregate sent the weighted mean values of all profiles investigated. stability test was conducted by wet sieving method as Full profile information (analytical data) on physical and outlined in USDA-NRCS (2014). It involves abrupt sub- chemical characteristics is presented for four sample mergence of air dry aggregates in water followed by wet profiles representing the two land use types and slope sieving using 0.5 mm sieve. Figures reported are percent- classes. age of aggregates retained after wet sieving. Soil moisture contents (w/w, %) were determined by means of pressure Results and discussion membrane extractor at different pressure forces to the Soil physical characteristics as affected by land use type crushed samples (Baruah and Barthakur 1997). The field and slope class capacity (FC) was determined at 1/3 bar and the perma- The soils are clayey with clay content ranging from 51 to nent wilting point (PWP) at 15 bars for sieved and air dry 55% in the A-horizon and from 58 to 72% in the B-hori- soil samples. The plant available water content (AWC) zon (Table 3). The clay enrichment in the B-horizon is as was determined as the difference between FC (the upper result of clay migration. The silt/clay ratio ranges from limit) and PWP (the lower limit). 0.28 to 0.41 in the A-horizon and from 0.22 to 0.41 in Soil pH was determined in water (pH—H O) using a the B-horizon that were rated as high according to the 1:2.5 soil to water solution ratio with a pH meter as out- ratings of Hazelton and Murphy (2007). This suggests lined in Van Reeuwijk (2006). Organic carbon (OC) con- the presence of weatherable mineral reserve in the soil. tent of the soil was analyzed using the Walkley and Black −3 The bulk density was within 1.04–1.14  g  cm range in method (Nelson and Sommers 1982). Total nitrogen (TN) −3 the A-horizon and 1.02–1.12  g  cm in the B-horizon. was analyzed according to the Macro-Kjeldahl method These values are below the critical values for agricultural that involves digestion of the sample and a wet-oxidation −3 use (1.4 g cm ) suggested by Hillel (2004) indicating the procedure (Bremner and Mulvaney 1982). Available phos- absence of excessive compaction or restrictions for root phorus (AP) content was determined using Olsen development. Land use and slope significantly (p  <  0.05) affected In Ethiopia, the Olsen’s NaHCO method (pH 8.5) is widely used for particle size distribution and plant available water con- determining soil available P. A study on the evaluation of soil test meth- tents. The mean values of fine grained texture materi - ods for available phosphorus on 32 Ethiopian soils reported that the Olsen als including 39% fine sand, 42% fine silt and 67% clay method followed by Warren and Cooke, and Truog methods is the best of the eight chemical methods they used to assess available P (Mamo and in the agroforestry system were significantly higher Hague (1991). This was further confirmed by Mamo, Christian and Heilig- than 30% fine sand, 21% fine silt and 46% clay in the tag (2002) who found the magnitude of soil available P extraction in the cereal system (Tables  4, 5). These findings suggest that order Truog > CAL > Olsen > Bray II > Warren and Cooke. Since Troug and CAL methods are not practiced in the analytical labs in Ethiopia, the although texture is an inherent property of the soil, it Olsen, Cole, Watanabe and Dean (1954) remains the best method for avail- can be altered by land use practices over a longer period able P-extraction in Ethiopia to date. Elias Environ Syst Res (2017) 6:20 Page 8 of 15 Table 3 Particle size distribution, textural class and bulk density of Nitisol sample profiles Horizon Depth (cm) Sand (%) Silt (%) Clay (%) Silt/clay Class BD (g/cm ) Profile 1: Intensive cereal upper slope (ET_ASAAP002) Ap 0–20 30 19 51 0.28 Sandy clay 1.14 AB 20–40 26 16 58 0.27 Clay 1.07 Bt1 40–80 22 18 60 0.30 Clay 1.02 Bt2 80–200 27 11 62 0.20 Clay 1.20 Profile 2: Intensive cereal lower slope (ET_AJJIP001) Ap 0–20 14 21 63 0.35 Clay 1.12 AB 20–42 12 21 67 0.31 Clay 1.10 Bt1 42–90 12 18 70 0.26 Clay 1.10 Bt2 90–200 10 20 72 0.27 Clay 1.10 Profile 3: Agroforestry upper slope (ET_JIMLS-SP2) Ah 0–12 23 23 55 0.41 Clay 1.14 BA 12–30 13 23 63 0.36 Clay 1.12 Bt1 30–0 12 26 61 0.43 Clay 1.12 Bt2 90–145 12 29 60 0.48 Clay 1.04 Bt3 145–200 12 27 62 0.43 Clay 1.06 Profile 4: Agroforestry lower slope (ET_JIM-G-SLP2 Ap 0–10 17 37 56 0.33 Clay 1.04 AB 10–30 14 22 64 0.15 Clay 1.02 Bt1 30–60 13 21 66 0.32 Clay 1.04 Bt2 60–105 11 22 63 0.42 Clay 1.07 Bt3 105–180 8 27 66 0.41 Clay 1.04 BD bulk density of time (Schaetzl and Anderson 2005). Slope effect was different between land use types (Table  7). This indicates also significant for particle size distribution. The mean that Nitisols have little water dispersible aggregates and values of fine sand (39%), fine silt (30%) and clay (63%) in hence they are fairly resistant to erosion. This is part the lower slope were significantly (p < 0.05) higher than of the reason why the Nitisols remained deep and pro- mean values in the upper slope—17% fine sand, 14% fine ductive in spite of centuries of intensive cultivation and silt and 51% clay in the upper slope (Table  6). The find - severe erosion hazards in the Ethiopian highlands (Elias ings suggest residual accumulation of coarser particles 2016). and removal of finer particles from in the upper slopes The water content of the soil at FC (1/3 bar) and PWP by runoff water and its deposition in the lower slopes. (15  bar) were 35 and 23% in the cereal system and 37 The result is in agreement with the findings of Gebrese - and 24% in the agroforestry system (Table  5). According lassie et  al. (2015) and Gebrekidan and Negassa (2006) to the rating of Hazelton and Murphy (2007), the water that reported increasing trends of coarse fractions with content at FC and PWP were rated as high while AWC increasing slope and increasing clay fractions with was in the medium to high range. The generally favour - decreasing slope gradients. able water holding capacity of the soil can be attributed Soil structural aggregate stability has a key role in to high clay content, well-developed soil structural aggre- the functioning of soil such as water retention, aera- gates and reasonably good organic matter contents of the tion, infiltration and therefore resistance to erosion soils. The result is in agreement with another report from (Abrishamkesh et al. 2010; USDA-NRCS 2014). The man Welega, western Ethiopia that found higher water hold- values of water stable aggregate (WSA), the proportion ing capacity for soils with higher clay content (Chimdi of structural aggregates retained after wet sieving in et  al. 2012). On the other hand, the mean AWC in the 0.5  mm sieve, were 79 and 87% for the intensive cereal agroforestry system (135 mm/m) was significantly higher and agroforestry systems, respectively (Table 5). Accord- than that in the cereal system (112  mm/m) suggesting ing to the ratings of Hazelton and Murphy (2007), the differences in particle grain size distribution and organic WSA was rated as very high and were not significantly matter content. Elias Environ Syst Res (2017) 6:20 Page 9 of 15 Table 4 Grain size fractionation of sand (>0.05 mm) and silt (0.05–0.002 mm) particles (%) Horizon Depth (cm) CS MS FS CSi MSi FSi Profile 1: Intensive cereal upper slope (ET_ASAAP002) Ap 0–20 62 20 18 52 27 21 AB 20–40 64 15 21 66 20 14 Bt1 40–80 62 22 16 45 20 35 Bt2 80–200 58 21 21 56 27 17 Profile 2: Intensive cereal lower slope (ET_AJJIP001) Ap 0–20 13 13 64 39 18 43 AB 20–42 12 22 66 20 25 55 Bt1 42–90 18 20 62 28 15 55 Bt2 90–200 16 22 62 13 24 63 Profile 3: Agroforestry upper slope (ET_JIMLS-SP2) Ah 0–12 45 21 34 55 25 25 BA 12–30 50 18 32 68 23 11 Bt1 30–90 48 20 32 51 34 15 Bt2 90–145 42 35 23 30 42 28 Bt3 145–200 45 27 28 44 36 20 Profile 4: Agroforestry lower slope (ET_JIM-G-SLP2) Ap 0–10 12 23 65 20 14 66 AB 10–30 10 28 62 39 19 42 Bt1 30–60 7 30 63 29 23 57 Bt2 60–105 17 25 63 29 20 51 Bt3 105–180 15 30 55 28 24 48 CS coarse sand, MS medium sand, FS fine sand; CSi coarse silt, MS medium silt, FSi fine silt Soil chemical characteristics as affected by land use The mean OC content was 2.0 and 2.1% for the inten - and slope sive cereal and agroforestry systems (Table  10). Based Tables 8 and 9 summarize important chemical character- on the ratings of Landon (1991), the OC of the soil istics of the sample profiles of Nitisols while mean values was rated very low showing no significant difference as affected by land use type and slope class are presented between the land use types. On the other hand, slope in Tables  10 and 11. The mean pH values were 5.29 and effect was significant (p  <  0.05) with higher mean val - 6.12 for the cereal and agroforestry systems (Table  8) ues (2.5% OC) in the lower slope compared to 1.5% which are statistically significantly (p  <  0.05) different. in the upper slope (Table  11). This is attributed to the Based on the ratings of Hazelton and Murphy (2007), the movement of humus particles down slope with runoff soil pH is rated as strongly acidic and moderately acidic water. The finding is in agreement with Gebreselassie respectively. The strongly acidic soil reaction in the cereal et al. (2015) that reported increasing OC contents with system was attributed to intense leaching of bases and decreasing slope. continued application of DAP and urea fertilizers. The The mean TN values, 0.15 and 0.22% for the inten - base saturation 62 and 77% for the cereal and agrofor - sive cereal and agroforestry systems, were rated low estry systems that are significantly (p  <  0.05) different based on the ratings of Landon (1991) and significantly (Table  10). The implication is that there is more intense (p  <  0.05) different between the two land use types. leaching of basic cations in the cereal system resulting in Higher TN content in the agroforestry system was due higher exchangeable acidity. In addition, the rate of fer- to crop residues addition and leaf litter accumulation tilizer application in the cereal system (100  kg urea and from land use practices that added to N-mineraliza- −1 150  kg DAP ha ) was double the rate applied in the tion. This is further elaborated by significantly lower −1 agroforestry system (i.e., 50 kg DAP and 75 kg urea ha ). C/N ratios with mean value of 10 in the agroforestry Previous research findings suggest that continuous appli - system compared to 18 in the intensive cereal system cation ammonia fertilizers such as DAP and urea can (Table  10). Although rate of decomposition was not contribute to increased exchangeable acidity of the soil measured in this study, the significantly higher C/N (Smaling and Braun 1996; Elias et al. 1998; Elias 2016). ratios are indicative of somewhat depressed microbial Elias Environ Syst Res (2017) 6:20 Page 10 of 15 Table 5 Structural aggregate stability and water holding capacity of Nitisol sample profiles Horizon Depth (cm) Water stable aggregates Water holding capacity (%) (%) −1 FC (1/3 bar) PWP (15 bar) AWC (mm m ) Profile 1: Intensive cereal upper slope (ET_ASAAP002) Ap 0–20 63 34 22 120 AB 20–40 70 35 23 120 Bt1 40–80 79 38 26 120 Bt2 80–200 76 40 28 120 Profile 2: Intensive cereal lower slope (ET_AJJIP001) Ap 0–20 85 38 26 120 AB 20–42 88 42 29 130 Bt1 42–90 89 43 30 130 Bt2 90–200 91 46 31 150 Profile 3: Agroforestry upper slope (ET_JIMLS-SP2) Ah 0–12 78 39 25 140 BA 12–30 75 37 23 140 Bt1 30–90 74 38 24 140 Bt2 90–145 69 36 22 140 Bt3 145–200 70 38 23 150 Profile 4: Agroforestry lower slope (ET_JIM-G-SLP2 Ap 0–10 91 40 23 170 AB 10–30 88 47 32 150 Bt1 30–60 93 47 31 160 Bt2 60–105 93 48 31 170 Bt3 105–180 94 49 26 230 Table 6 Mean values of physical and chemical characteristics of Nitisol (0–20 cm) as affected by slope class Soil properties Upper slope (15–30%) Lower slope (2–5%) T value Sign. Sand (%) 27 12 4.829 0.017 Silt (%) 22 25 −0.441 0.689 Clay (%) 51 63 −1.604 0.027 −3 Bulk density (g cm ) 1.2 1.1 1.787 0.172 Particle size fractions (%) Coarse sand 49 15 3.141 0.042 Medium sand 34 33 0.097 0.929 Fine sand 17 52 −4.447 0.041 Coarse silt 54 41 1.065 0.365 Medium silt 32 21 1.392 0.258 Fine silt 14 38 −2.637 0.078 Water stable aggregates 80 82 −0.935 0.419 Water holding capacity w/w, %) FC (1/3 bar) 35 37 −1.095 0.353 PWP (33 bar) 23 24 −0.662 0.555 −1 AWC (mm m ) 120 127 −1.567 0.215 decomposition of organic matter and N-mineraliza- remains subject for future research. Slope effect of TN tion in the cereal system. Further, the land use system was also significant (p < 0.05) with higher mean values might be adversely affecting soil microorganisms which in the lower slope (0.22%) compared to 0.13% in the Elias Environ Syst Res (2017) 6:20 Page 11 of 15 Table 7 Mean values of physical and chemical characteristics of Nitisols (0–20 cm) as affected by land use Soil property Intensive cereal system Agroforestry based system T value Sign. Sand (%) 28 15 3.677 0.032 Silt (%) 26 18 −2.320 0.103 Clay (%) 46 67 −5.536 0.012 −3 Bulk density (g cm ) 1.2 1.1 1.163 0.329 Particle size fractions (%) Coarse sand 43 19 6.453 0.008 Medium sand 41 16 4.494 0.021 Fine sand 30 39 −3.307 0.045 Coarse silt 59 30 7.769 0.004 Medium silt 38 17 3.859 0.031 Fine silt 21 42 −3.23 0.045 Water stable aggregates 79 87 −3.068 0.055 Water holding capacity w/w, %): FC (1/3 bar) 35 37 −1.424 0.250 PWP (33 bar) 23 24 −0.132 0.903 AWC (mm/m) 112 135 −9.000 0.003 Table 8 Selected chemical characteristics of Nitisol profiles by land use type and slope −1 Horizon Depth (cm)PH H O OC (%) TN (%) C/N CEC and exchangeable bases (cmol(+) kg ) CEC Ca Mg Na K TEB PBS Profile 1: Intensive cereal upper slope (ET_ASAA-P002) Ap 0–20 4.8 2.1 0.16 13 44 15 4 0.1 1.4 20 43 AB 20–40 5.1 1.7 0.10 17 32 14 3 0.1 1.2 18 53 Bt1 40–80 5.5 1.0 0.05 20 30 13 2 0.1 1.3 16 50 Bt2 80–200 5.7 1.0 0.06 17 30 14 4 0.2 1.2 19 60 Profile 2: Intensive cereal lower slope (ET_AJJI-P001) Ap 0–20 4.7 3.6 0.20 18 42 15 7 0.4 1.2 22 52 AB 20–42 4.9 2.0 0.12 17 49 20 7 0.4 1.1 27 55 Bt1 42–90 4.5 1.1 0.06 18 48 20 6 0.5 1.4 26 54 Bt2 90–200 4.9 1.1 0.07 15 45 17 5 0.4 1.3 22 49 Profile 3: Agroforestry upper slope (ET_JIMLS-SP2) Ah 0–12 6.2 2.5 0.25 10 37 13 14 0.2 2.2 29 78 BA 12–30 5.5 1.3 0.12 11 41 18 10 0.6 2.0 29 70 Bt1 30–90 5.5 0.9 0.09 10 35 14 10 0.9 2.0 25 71 Bt2 90–145 5.3 0.6 0.06 10 32 14 8 0.2 2.1 23 72 Bt3 145–200 5.8 0.4 0.04 10 30 12 11 0.2 2.0 18 77 Profile 4: Agroforestry lower slope (ET_JIM-G-SLP2) Ap 0–10 5.5 3.6 0.33 11 30 11 8 0.2 3.0 21 70 AB 10–30 5.9 1.9 0.13 14 28 13 8 0.1 2.0 22 79 Bt1 30–60 5.6 1.5 0.13 12 27 12 9 0.1 2.2 22 81 Bt2 60–105 5.6 1.1 0.10 11 30 12 10 0.1 2.4 23 77 Bt3 105–180 5.5 0.4 0.03 12 30 14 8 0.1 2.2 23 76 TEB total exchangeable bases, PBS percent base saturation −1 upper slope (Table  11). Similar results are reported by The mean AP content, 10 and 8  mg  kg for the cereal Gebreselassie et  al. (2015) who found increasing TN and agroforestry systems, were rated as low based on levels with decreasing slope. the ratings of Hazelton and Murphy (2007). Although Elias Environ Syst Res (2017) 6:20 Page 12 of 15 −1 Table 9 Available phosphorus and micronutrient contents (mg kg ) of the surface horizons in the Nitisol profiles Profile ID Land use Slope AP Fe Mn Zn Cu ET_ASAA-P002 Cereal 15–30 8 29 63 3 2 ET_AJJI-P001 Cereal 2–5 16 32 69 2 2 ET_JIMLS-SP2 Agroforestry 15–30 9 66 94 13 3 ET_JIM-G-SLP2 Agroforestry 2–5 8 60 98 10 2 Table 10 Mean values of selected chemical characteristics of Nitisols (0–20 cm) as affected by land use Soil property Intensive cereal system Agroforestry based system T value Sign pH–H O 5.29 6.12 −6.935 0.006 OC (%) 2.00 2.12 −0.620 0.579 Tot. N (%) 0.15 0.22 −4.217 0.024 C/N 18 10 2.600 0.080 −1 AP (mg kg ) 10.0 8 0.504 0.649 −1 CEC and basic cations (cmol(+) kg ): CEC 40 44 1.800 0.170 Ca 14 16 −1.507 0.229 Mg 6 15 −10.832 0.002 Na 0.02 0.14 0.522 0.638 K 1.60 3.0 −3.705 0.024 PBS (%) 51 75 −6.937 0.006 −1 Micronutrients (mg kg ): Fe 37 97 −8.895 0.003 Mn 39 68 −9.731 0.002 Zn 3 13 −8.278 0.004 Cu 2 3 −1.732 0.182 Table 11 Mean values of  selected chemical characteristics some profiles in the cereal system had high AP contents of Nitisols (0–20 cm) as affected by slope (Table  9), the mean values were not significantly differ - ent between the two land use types. The low levels of AP Soil properties Upper slope Lower slope T value Sign. (15–30%) (2–5%) in spite of relatively higher doses DAP application (i.e., −1 150 kg ha ) in the cereal system suggests the unavailabil- pH–H O 5.85 5.67 0.835 0.465 ity of the applied phosphate in the soil solution. This was OC (%) 1.50 2.52 −12.000 0.000 attributed to increased exchangeable acidity and higher Tot. N (%) 0.13 0.22 −4.869 0.012 P-sorption capacity of the strongly acidic soils under the C/N 8 15 −25.000 0.000 cereal system. Literature indicates the applied phosphate is −1 AP (mg kg ) 10.0 17.0 −5.085 0.015 fixed by iron and aluminum compounds (i.e., sesquioxides) −1 CEC and basic cations (cmol(+) kg ): and hence, rendered unavailable in the soil solution in low CEC 43.0 42.0 0.324 0.767 pH soils (Schaetzl and Anderson 2005; Hillel 2004). On the Ca 16.0 14.0 1.842 0.163 other hand, AP contents were significantly (p < 0.05) differ Mg 9.0 8.0 5.196 0.14 ent between the two slope classes with higher mean values Na 0.04 0.06 −0.16 0.923 −1 −1 (17 mg kg ) in the lower slope compared to 10 mg kg in K 1.2 1.4 −1.092 0.355 the upper. The conventional practice of farmers is to apply PBS (%) 62.0 58.0 1.960 0.145 DAP at planting (i.e., basal application) when the monsoon −1 Micronutrients (mg kg ): rains are at their peak that results in the runoff removal of Fe 61.0 68.0 −0.733 0.516 some of the applied fertilizer from the upper slopes that Mn 46.0 55.0 −1.741 0.180 are deposited in the lower slopes. Zn 9.0 9.0 1.000 0.391 2+ On the other hand, the CEC, exchangeable bases (Ca , Cu 3.0 2.0 0.775 0.95 2+ + Mg, K ) and PBS of the soil were rated high based on the Elias Environ Syst Res (2017) 6:20 Page 13 of 15 ratings of Landon (1991) while N a appeared only in trace plant available water contents (AWC), soil pH and OC, amount. The paired T-test showed no significant difference TN, AP exchangeable basses and some micronutrients. 2+ between land use type and slope classes except for M g , The land use practices in the intensive cereal system was + 2+ −1 + K and PBS. Mean values of M g (15  cmol(+) kg), K found to be adversely affecting important soil physical −1 (3 cmol(+) kg ) and PBS (75%) in the agroforestry system and chemical characteristics as compared to the agro- were significantly higher than those in the cereal system (6 forestry system. These include alteration of particle size −1 2+ + and 1.6  cmol(+) kg of Mg and K and 51% PBS). The distribution, strongly acidic soil reaction, organic matter PBS was in the medium to high range (43–60%) in the cereal depletion, multiple nutrient deficiencies (N, P, K and Zn) system while it was high to very high (70–81%) in the agro- and low plant available water content. Among the inap- forestry system (Table 8). The generally high base saturation propriate land use practices include repeated cultivation of the soil was consistent with high contents of exchange- to create fine seedbed that predisposes the soil to ero - 2+ 2+ able bases (chiefly Ca and Mg ) but not consistent with sion, unbalanced fertilizer application, rotation of maize generally acidic soil reaction (pH 5.5–6.2) that needs some with potato that are depleting some nutrient stocks (e., K explanation. First, the soils in the Ethiopian highlands have and Zn), and removal of crop residues from fields. As can developed on recent Trapean lava flows that have high base be seen from the significantly lower PBS in the cereal sys - status (Mohr 1971). Secondly, according to Buol et al. (2011) tem, leaching of basic cations was intense that resulted in the volcanic parent materials such as rhyolites, granite, tra- increased levels of exchangeable acidity. In addition, con- chytes, ignimbrites, andesites and some acidic basalts that tinued use of DAP and urea seems to have contributed dominate the Ethiopian produce inherently acidic clays. to increased exchangeable acidity as well as accentuating Thirdly, the humid climatic conditions might have resulted the uptake and deficiency of other nutrients such as K in increased microbial oxidation to produced organic and Zn that are not supplied in the fertilizer application. acids, which provide H to the soil that can also contribute Slope position of the profiles also had significant effect towards low soil pH (Schaetzl and Anderson 2005). on soil characteristics with significantly higher propor - 2+ 2+ 2+ 2+ The mean values for Fe, Mn, Zn and Cu were tions of coarse textured particles that were low in OC, AP −1 respectively 37, 39, 3 and 2  mg  kg in the cereal system and TN contents in the upper slope compared to lower −1 while it was 97, 68, 13 and 3  mg  kg in the agroforestry slopes. Organic matter and nutrient contents decreased system (Table  9). According to the ratings of Havlin et al. with increasing slope gradient particularly in the cereal (1999), the micronutrient contents were rated as high to system indicating the effect of erosional losses of fine very high except for Z n that was low to medium. The high particles. levels of micronutrients is consistent with the low pH of The data, therefore, provides useful information for 2+ the soil and the low Zn contents are in agreement with planning soil management strategies that can address previous report that indicated widespread Zn deficiency in adverse effects of land use on soil characteristics. First the Nitisol areas of the Ethiopian highlands (Dibabe et al. and foremost, application of more balanced blend ferti- 2007). According to FAO (2006b), low soil pH induces lizer that contains N, P, K and Zn combined with liming increase in micronutrient contents that may eventually to raise the soil pH remains crucially important. In this lead to root toxicity unless soil pH is corrected through connection, research needs to generate NPS and Zn-B liming. The paired T-test showed significant (p < 0.05) dif - blend fertilizer applications rates for different crops, soil 2+ 2+ 2+ ference between land use types for Fe, Mn , and Zn types and land use systems. Increasing the rate of fer- 2+ but slope effect was nonsignificant. The mean value of Fe tilizer application is particularly crucial in the agrofor- −1 2+ −1 2+ −1 (97 mg kg), Mn (68 mg kg ) and Zn (13 mg kg ) in estry based system where current rates of fertilizer use the agroforestry system were significantly higher than 37, are far too low. However, given the very high levels of −1 2+ 2+, 2+ 39 and 3  mg  kg of Fe, Mn and Zn in the cereal Zn in the soil, Zn-blend should not be extended to farm- system (Table  10). According to Mohr (1971) and David- ers in the agroforestry system. Secondly, organic matter son (1983), the soil parent materials in the agroforestry management including restitution of crop residues and system are dominated by basic rocks such as alkali-olivine recycling of farm yard manure is fundamental in order basalts, amphibole and mica that are rich in ferromanga- to reverse the OC depletion and increase water hold- 2+ nese minerals thus explaining the exceptionally high F e ing capacity of the soil. Third, although Nitisols have 2+ and Mn contents in these sites. high structural aggregate stability that are fairly resist- ant to erosion, their landform of occurrence (i.e., high Conclusion to mountainous relief hills with steep slopes) makes The study showed that land use practices and slope class the soils susceptible to degradation by water erosion. significantly affects important soil physical and chemical This calls for the implementation of integrated soil and characteristics. These include particle size distribution, water conservation measures that combine physical, Elias Environ Syst Res (2017) 6:20 Page 14 of 15 Received: 13 January 2017 Accepted: 8 August 2017 biological and agronomic measures mainly in the cereal system. In addition, soil textural fractionation analysis indicates that repeated tillage practice is found to pre- dispose the soil to erosion by adversely affecting the soil textural fractions. Therefore, minimum tillage combined References with legume rotation (maize-tef-bean) observed in some Abrishamkesh S, Gorji M, Asadi H (2010) Long-term effects of land use on soil aggregate stability. Int Agrophys 25:103–108 parts of west Gojam (e.g., South Achefer and Bure) need Assen M, Amd Tegene B (2008) Characteristics and classification of the soils to be widely disseminated among farmers in the cereal- of the plateau of Siemen Mountains National Park. SINET Ethiopia J Sci livestock highlands. 31(2):89–102 Baruah TC, Barthakur HP (1997) A textbook of soils analysis. Vikas Publishing House, New Delhi Bouyoucos GJ (1962) Hydrometer method improvement for making particle Abbreviations −1 size analysis of soils. Agronomy 5:179–186 AP: available phosphorus (mg kg ); AWC: available water content; BD: bulk 3 Bremner JM, Mulvaney CS (1982) Total nitrogen. In: Page AL, Miller RH, Keeney density (dgcm ); C/N: carbon to nitrogen ratio; Ca/Mg: calcium to magnesium −1 −1 DR (ed) Methods of soil analysis II. Chemical and microbiological proper- ratio; CEC: cation exchange capacity (cmol(+) kg ); Cu: copper (mg kg ); ties. American Society of Agronomy, Soil Science Society of America DAP: di-ammonium phosphate (18% N, 46% P O ); FC: field capacity; ITCZ: 2 5 −1 Buol SW, Southard RJ, Graham RC, McDaniel PA (2011). Soil genesis and clas- Inter Tropical Convergence Zone; K: Potassium (cmol(+) kg ); Mg: Magne- −1 −1 −1 sification, 6th edn. Wiley-Blackwell, London sium (cmol(+) kg ); Mn: Manganese (mg kg ); Na: Sodium (cmol(+) kg ); Chimdi A, Gebrekidan H, Kibret K, Tadesse A (2012) Status of selected physico- PBS: percent base saturation; SC: sandy clay; TN: total nitrogen (%); PWP: −1 chemical properties of soils under different land use systems of Western permanent wilting point; WSA: water stable aggregates; Zn: zinc (mg kg ). Oromia, Ethiopia. J Biodivers Environ Sci 2(3):57–71 Davidson A (1983) The Omo river project: reconnaissance geology and geo- Author’s information chemistry of parts of Ilubabor, Kafa, Gamo Gofa, and Sidamo. Ethiop Instit The author is a Ph.D. working in the area of Soil Science and environment Geol Surv 2:1–89 having 20 years of post-Ph.D. research, teaching and development work. Dibabe A, Bekele T, Assen Y (2007) The status of micronutrients in Nitisols, Currently, he holds associate Professor’s position with College of Natural and Vertisols, Cambisols and Fluvsisols in major maize, wheat, tef and citrus Computational Science of Addis Ababa University. Over the past years, he growing areas of Ethiopia. Ethiopian Agricultural Research Organization has been working on soil survey, characterization and mapping work with (EARO) Research Report, Addis Ababa scientists from the Wageningen University and Research Centre and the Elias E (2002) Farmers perceptions of soil fertility change and management. In: International Soil Reference and Information Centre (ISRIC), the Netherlands. SOS-Sahel and institute for sustainable development, Addis Ababa Some of his work has recently been published in a book entitled, “Soils of the Elias E (2016) Soils of the Ethiopian highlands: geomorphology and properties. Ethiopian Highlands: Geomorphology and Properties”—ISBN: 978-99944- ALTERA Wageningen University Research Centre, The Netherlands. ISBN: 952-6-9. In addition, the author published a number of peer reviewed journal 978-99944-952-6-9 articles and book chapters previously. Elias E, Morse S, Belshaw DG (1998) Nitrogen and phosphorus balances of Kindo Koisha farms in southern Ethiopia. Agric Ecosyst Environ 71(1):93–113 Eswaren H (1988) Taxonomy and management related properties of the red Acknowledgements soils of Africa. In: Nyamapfene K, Hussein J, Asumadu K (eds) The red soils The author acknowledges the technical support of CASCAPE field staff in the of eastern and southern Africa. Proceedings of an international sympo- study sites. These technical assistance do not qualify for co-authorship since sium, Harare, pp 1–23 data accrual, analysis, interpretation and write was done solely by the author. FAO (1984) Geomorphology and soils of Ethiopia. In: Assistance to land use planning and provisional soil association map of Ethiopia. Field document Competing interests AG DP/ETH/78/003. Food and Agriculture Organization of the UN, Rome The authors declares that there is no financial or non-financial competing FAO (1986) The Ethiopian highlands reclamation study (EHRS). vol 1, In: Main interests. Report. Food and Agriculture Organization of the UN, Rome FAO (2001) Lecture notes on the major soils of the world. In: ISRIC-ITC-Catholic Availability of data and materials University of Leuven World soil resources Report No 94. Food and Agri- I declare that the data and materials presented in this manuscript can be culture Organization, Rome made publically available by Springer Open as per the editorial policy. FAO (2006a) Guideline for soil description. 4th edn, Food and Agriculture Organization of the UN, Rome Consent for publication FAO (2006b) Plant nutrition for food security: a guide for integrated nutrient The manuscript does not contain no data or information from any person or management. In: FAO fertilizer and plant nutrition, vol 16. Food and individual apart from his own field investigation. All data and information are Agriculture Organization of the UN, Rome generated and synthesized by the author himself. Gebrekidan H, Negassa W (2006) Impact of land use and management prac- tices on chemical properties some soils of Bako area, western Ethiopia. Ethics approval and consent to participate Ethiop J Nat Res 8(2):177–197 Not applicable to this manuscript submission. Gebreselassie Y, Anemut F, Addis S (2015) The effects of land use types, man- agement practices and slope classes on selected soil physico-chemical Funding properties in Zikre watershed, North-Western Ethiopia. Environ Syst Res This research was conducted as part of the action research and capacity 4(3):1–7. doi:10.1186/s40068-015-0027-0 building project entitled, “Capacity building for Scaling up of Evidence based Haileslassie A, Priess J, Veldkamp E, Teketay D, Lesschen JP (2005) Assessment best Practices for increased Agricultural Production in Ethiopia (CASCAPE)” of soil nutrient depletion and its spatial variability on smallholders’ mixed with kind financial assistance from the Ministry of Foreign Affairs of the Dutch farming systems in Ethiopia using partial versus full nutrient balances. Government through its Embassy in Addis Ababa. Agric Ecosyst Environ 108:1–16 Hailu H, Mamo T, Keskinen R, Karltun E, Gebrekidan H, Bekele T (2015) Soil Publisher’s Note fertility status and wheat nutrient content in Vertisol cropping systems of Springer Nature remains neutral with regard to jurisdictional claims in pub- central highlands of Ethiopia. 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