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Soil nutrient assessment based on attribute recognition model in the Loess Plateau of China

Soil nutrient assessment based on attribute recognition model in the Loess Plateau of China Soil fertility is important factors for growth and productivity of vegetation. The relationship between vegetation and soil fertility deserves attention due to its scientific importance and practical applications. However, the effects of soil fertility on vegetation development and succession are poorly documented. Here we study soil fertility in Yanhe watershed at northern Shaanxi on five different land uses, namely shrubland, farmland, natural grassland, woodland, and artificial grassland, and in soil under restoration for 5, 10, 15, 20, and 25. Attribute recognition model based on entropy weight was used to evaluate the soil fertility of typical region in the Loess Plateau of China, which contained 52 soil samples with 6 physical and chemical indexes, including soil organic matter, soil total nitrogen, total phosphorus, etc. The results show that (1) Land use has an obvious effect on soil bulk density, total porosity and capillary porosity of surface layers, but not significant in the subsurface layer; (2) SOM, N , total N and K are the most in shrubland and woodland while P and P in farmland, respectively; hydro avail total avail (3) Vegetation succession on eroded soil result in significant changing of soil fertility; and (4) Vegetation succession on eroded soil result in significant changing of soil fertility. Introduction degradation and supply of fuel and fodder in this area, and Soil fertility is important factors for growth and pro- reduced nutrients retention [14]. Deterioration of soil fer- ductivity of vegetation [1-3]. Vegetation structure, soil tility is important in vegetation restoration, especially for moisture and nutrients have very close relationship. converting agricultural land to reforested plantations or Different soil nutrients affect vegetation community grassland. This topic is also important in estimating the the size of the biomass, species composition and diver- role of natural vegetation recovery in soil rehabilitation of sity [4]. Soil nitrogen determines the productivity, biodi- the Loess Plateau, where little natural vegetation exists, versity and species invasive capacity of vegetation helping to guide current restoration of vegetation in west communities [5-7]. Phosphorus is a restrictive factor in a China. variety of soil types, and determines the size of vegetation Study of degradation processes attracts attention to productivity and change of species composition [8-12]. the influence of degradation on the human environment, Potassium also affects community biomass [10] and state but study of recovery processes is more important, pro- of vegetation water, and help to overcome soil moisture viding recommendations for eco-environmental recon- stress [13]. So, in vegetation restoration and reconstruc- struction or rehabilitation. Much research has been done recently on the influence on soil fertility properties tion, it is should be considered that soil properties of aban- doned farmland to assure that the ideal and realistic of vegetation recovery or different land-use patterns restoration goals [4]. However, over exploitation of exist- [15-17]. However, changes of soil fertility properties are ing vegetation further aggravates the problem of land still under study during the long-term recovery of vege- tation. Research into changes of soil fertility properties is considered necessary to understand the ecological * Correspondence: Jiaof11@126.com Institute of Soil and Water Conservation, Northwest A&F University, Yangling, consequences of vegetation recovery [18,19]. In the Shaanxi, China semiarid area of the Plateau, vegetation recovery or Full list of author information is available at the end of the article © 2013 Jiao et al.; licensee Springer This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Jiao et al. SpringerPlus 2013, 2(Suppl 1):S14 Page 2 of 6 http://www.springerplus.com/content/2/S1/S14 reconstruction is always limited by shortage of fertility. northern Shaanxi Province and had 25 years of compre- There is not much literature concerned with this parti- hensive management because one ecology station was cular issue, especially for long-term change of soil ferti- founded in this area (Figure 1). Of the area, 287 km of lity properties under natural re-vegetation in the Plateau length, 7687 km2 of the total area; 90% is hilly, 3% is [20]. The objective of the present study is to identify villages, rivers, and lakes; and only 7% is considered sui- changes in soil fertility in five different land uses includ- tablefor intensiveagriculture.The studyareahas a ing shrubland, natural grassland, artificial grassland, semi-arid climate characterized by heavy seasonal rain- farmland, and woodland, and changes in soil fertility after fall with periodic local flooding and drought; the average different restoration periods of plantations. We hypothe- annual rainfall at the experimental site is 497 mm sized that soil fertility properties are largely a function of (1970-2000, CV22%) with distinct wet and dry seasons. secondary succession re-growth. Other important factors, The rainy season starts in July and continues up to such as neighboring vegetation, climate change, and alti- October; the August rainfall accounts for 23% of the tude were not considered. The most popular natural grass- annual rainfall. The annual reference evapotranspiration land in the study area with vegetative chronosequence is is approximately 1000 mm. Most of the lands are also investigated to evaluate soil fertility on lands with dif- located at 900-1500 m altitude and are closely dissected ferent restoration times. and sharp-edged with steep and very steep slopes (the slopes are deep, 40%). The topography, soil type, soil Materials and methods and land-use patterns of Yanhe watershed are very typi- Study area cal in the Loess Plateau, Land-use types including: slop- The study area was located in Yanhe watershed of the ing land, terraces, orchards, woodland, shrubland, Loess Plateau at N 36°23′-37°17′and E 108°45′-110°28′ in natural grassland, wasteland and other types [21]. Figure 1 The location of study area on the Loess Plateau. Jiao et al. SpringerPlus 2013, 2(Suppl 1):S14 Page 3 of 6 http://www.springerplus.com/content/2/S1/S14 Study approach and sampling design properties can be measured by comparing sites of differ- The chronosequence method was used because of the ent ages. Five age series (5-, 10-, 15-, 20- and 25-year-old existence of similar conversion history in this area. The vegetation community) were found in the adjacent sites management was similar, with known periods of cultiva- of the study area, which have undergone light livestock tion climate, topography, and soil type. Soil samples were grazing in recent years. Within each community (5, 10, collected in August 2006. Soil samples were taken at 0-20 15, 20 and 25), five sites were selected as sampling (five cm depths. Composite samples of about 1 kg were col- replicates). Also, five nonvegetated lands in the vicinity of lected with 5 replicates at each sampling plot and then the planted sites (farmland) were chosen as a control for air-dried and sieved through 1 mm sieve. All measure- the chronosequence. ments were made at the State Key Laboratory of Soil Ero- sion and Dryland Farming on the Loess Plateau, China. Calculation of soil samples attribute measure and data The analytical methods for the soil samples were the analysis international standard methods as adopted and pub- Soil samples attribute measure is its status value in soil. It lished by the Institute of Soil Science, Chinese Academy is used that the second national soil survey classification of of Sciences (1978). Soil organic matter (SOM) was soil nutrient standards for the evaluation criteria, and a determined on the basis of oxidation with potassium standard matrix was built up based on the evaluation cri- dichromate in a heated oil bath. Total nitrogen (Ntotal) teria. Soil sample analysis of variance (ANOVA) and cor- was measured according to the semi micro Kjeldahl relation were carried out using the SPSS11.0 procedures method and hydrolysable nitrogen (Nhydro) by means for sites in different succession stages. Duncan’s test (at of the Alkali diffusion method. Total phosphorus (Pto- p < 0.05) was used to compare means of soil variables tal) was digested with perchloric acid and sulfuric acid when the results of ANOVA were significant at p < 0.05. and determined using colorimetry. Total potassium (Ktotal) was digested with hydrofluoric acid and per- Results and discussions chloric acid. Available phosphorus (Pavail) was extracted Soil fertility in different land uses with sodium bicarbonate and measured with colorime- Table 1 shows that, in different land use, changing try. Available potassium (Kavail) in soil was extracted SOM, Ntotal, Ptotal, Nhydro, Pavail and Kavail were sig- with ammonium acetate. nificant in the 0-20 cm layer at p < 0.05. Woodland A common approach in studies of soil rehabilitation in contains the highest all soil fertility indexes except relation to vegetative cover is to monitor plant and soil Pavail. Farmland contains the highest Ptotal (0.57%) and changes occurring along a vegetative chronosequence Pavail (2.06 mg/kg), and has a higher Kavail (60.2 mg/ developed on similar soils under similar climatic condi- kg). Natural grassland and Shrubland contain the high- tions [22]. This chronological approach has been widely est Kavail (70.0 mg/kg), and have higher SOM (8.11%) used in applied ecosystem research [23] and is considered and Ntotal (0.46%), respectively. While artificial grass- retrospective research because existing conditions were land has a lower contain in all soil fertility indexes. compared with known original conditions and treat- ments. The retrospective approach was adapted in this Weight of soil fertility index in different land uses study because of the availability of closely located vegeta- Table 2 shows that, in different land use, changing tion community established 5, 10, 15, 20 and 25 years weight of soil fertility index were significant in the ago on eroded soils with similar properties. These vegeta- 0-20 cm layer at p < 0.05. In the 0-20 cm layer, weight tion communities therefore provide a time gradient of of Nhydro was the highest in farmland, followed by grass occupancy on similar sites. Changes in soil SOM, Kavail, Pavail, Ntotal and Ptotal. Weight of SOM Table 1 Means and coefficient of variations of soil nutrient in different land-use patterns Land use SOM (%) N (%) P (%) N (mg/kg) P (mg/kg) K (mg/kg) total total hydro avail avail bc bc a cd a ab Farmland 6.87 (0.30) 0.44 (0.22) 0.57 (0.05) 26.5 (0.25) 2.06 (0.43) 60.2 (0.37) c c b d b b Artificial grassland 6.17 (0.32) 0.35 (0.22) 0.52 (0.03) 25.0 (0.12) 0.87 (0.64) 38.4 (0.15) b b b b b a Natural grassland 8.11 (0.24) 0.46 (0.32) 0.52 (0.12) 34.8 (0.23) 0.88 (0.13) 70.0 (0.27) a a a a b a Woodland 10.25 (0.19) 0.61 (0.15) 0.57 (0.06) 44.4 (0.19) 1.01 (0.37) 85.3 (0.47) bc b ab bc b a Shrubland 7.08 (0.27) 0.46 (0.27) 0.53 (0.08) 32.6 (0.27) 0.72 (0.34) 68.0 (0.39) Sig. of ANOVA 0.001 0.000 0.031 0.000 0.000 0.020 Means with the same letter in the same row are not significantly different at the 0.05 level (LSD). Data in the parentheses are coefficient of variation. Jiao et al. SpringerPlus 2013, 2(Suppl 1):S14 Page 4 of 6 http://www.springerplus.com/content/2/S1/S14 Table 2 Weight of soil nutrient index in different land use patterns Land use SOM N P N P K Sig. of ANOVA total total hydro avail avail b e f a d c Farmland 19.18 14.37 13.77 20.48 14.92 17.29 0.000 b bc cd de de a Artificial grassland 17.64 16.75 15.92 15.21 15.33 19.15 0.000 a c f b d e Natural grassland 21.09 17.87 11.53 19.17 15.72 14.62 0.000 c c bc a a ab Woodland 13.88 13.64 15.89 19.59 19.13 17.87 0.000 c c a b c c Shrubland 15.62 15.66 19.70 18.57 14.87 15.57 0.000 Means with the same letter in the same row are not significantly different at the 0.05 level (LSD). Data in the parentheses are coefficient of variation. was the highest in natural grassland, followed by Nhydro, Weight of soil fertility index in different restoration Ntotal, Pavail, Kavail and Ptotal. Compared with that in years farmland and natural grassland, weight of Kavail was the Figure 2 shows that, in different restoration years, chan- highest in artificial grassland, and weight of Nhydro and ging weight of soil fertility index was significant in the Pavail was the highest in Woodland, and weight of Ptotal 0-20 cm layer at p < 0.05. Abandoned early, the greater was the highest in Shrubland. In comparison, SOM, the weight and so are as follows: Pavail > Nhydro > Nhydro, Pavail and Kavail played an important role in SOM > Kavail > Ntotal > Ptotal. The difference between different land use. weights of soil fertility was significant at p < 0.05, the largest up 66.28% (Figure 2). With the increase of aban- doned years, the difference between weights of soil ferti- Soil fertility in different restoration years lity was reducing gradually. The largest differences Five replicated soil samples were collected from five between weights of soil fertility were 52.94%, 41.84%, sites with the same restoration time of 5, 10, 15, 20 and 30.97%, 23.04% and 11.01% in 5, 10, 15, 20 and 25 25 years, respectively. Also, five nonvegetated lands in the vicinity of the planted sites (farmland) were chosen years, respectively (Figure 2). The statistical results as controls for the chronosequence. After 5, 10, 15, 20 showed that: With the increase of abandoned years, and 25 years of restoration, SOM, Ntotal, Nhydro, Pavail affection of soil fertility on vegetation succession came and Kavail were significant in the 0-20 cm layer at p < into line gradually (Figure 2). 0.05 and except Ptotal, which was not significant at p > 0.05. Generally, vegetation succession resulted in a Conclusions change of soil fertility parameters in the eroded soils, Land use has an obvious effect on Soil fertility of surface significant decreases of soil fertility parameters (p < layer, but not significant in the subsurface layer. Shrub- 0.05) took place from beginning to 15-years of restora- land has higher soil fertility than other land uses. In tion, and significant increases (p < 0.05) from 15-years most cases, table land has low levels of soil fertility, but to 20-years of restoration, and significant decreases (p < after long period of cultivation, the land degrades year 0.05) from 20-years to 25-years of restoration. The sta- by year. Our results indicate that the establishment and tistical results showed that soil fertility and vegetation development of vegetation succession on eroded soil succession had significant interactions with all soil ferti- result in significant changing of soil fertility. With lity parameters except Ptotal (Table 3). increased plantation age, it is possible to recover soil Table 3 Means and standard deviations of soil nutrient in different restoration years Restoration time SOM(%) N (%) P (%) N (mg/kg) P (mg/kg) K (mg/kg) total total hydro avail avail de de d c c 25years 7.33 (1.31) 0.43 (0.07) 0.54(0.07) 29.3 (4.29) 0.70 (0.16) 64.9 (7.79) cde cde cd c c 20years 8.02 (1.47) 0.50 (0.15) 0.54(0.06) 31.9 (7.05) 0.67 (0.10) 66.0 (10.2) e e d c c 15years 5.93 (0.24) 0.36 (0.08) 0.54(0.06) 23.2 (2.68) 0.72 (0.10) 61.2 (17.2) e e d bc c 10years 5.53 (0.41) 0.37 (0.07) 0.54(0.04) 23.3 (4.62) 0.83 (0.18) 52.8 (20.5) de de d bc c 5years 6.62 (0.61) 0.43 (0.10) 0.53(0.03) 26.8 (5.99) 0.98 (0.17) 54.3 (27.4) de de d a c 0years 6.87 (0.30) 0.44 (0.22) 0.57(0.05) 26.5 (0.25) 2.06 (0.43) 60.2 (0.37) Sig. of ANOVA 0.000 0.000 0.627 0.000 0.000 0.003 Means with the same letter in the same row are not significantly different at the 0.05 level (LSD). Data in the parentheses are standard deviations. Jiao et al. SpringerPlus 2013, 2(Suppl 1):S14 Page 5 of 6 http://www.springerplus.com/content/2/S1/S14 Figure 2 Weight of soil fertility in different restoration years. 5. Chapin FS, Vitousek PM, Van Cleve K: The nature of nutrient limitation in fertility to a certain degree, and affection of soil fertility plant communities. American Naturalist 1986, 127:48-88. on vegetation succession came into line gradually. 6. Wedin DA, Tilman D: Influence of nitrogen loading and species composition on the carbon balance of grasslands. Science 1996, 274:1720-1723. Competing interests 7. Brooks ML: Effects of increased soil nitrogen on the dominance of alien The authors declare that they have no competing interests. annual plants in the Mojave Desert. Journal of Applied Ecology 2003, 40:344-353. Acknowledgements 8. Janssens F, Peeters A, Tallowin JRB, et al: Relationship between soil This study was sponsored by the Western Light Project of Chinese Academy chemical factors and grassland diversity. Plant and Soil 1998, 202:69-78. of Sciences (NO: 2010y236), the National Natural Sciences Foundation of 9. Kirkham FW, Mountford JO, Wilkins RJ: The effects of nitrogen, potassium China (NO: 40871246), and Foundation for Youths Teacher by Northwest and phosphorus addition on the vegetation of a Somerset peat moor A&F University. under cutting management. Journal of Applied Ecology 1996, 33:1013-1029. 10. Oomes MJM, Ol H, Altena HJ: Effects of vegetation management and Declarations raising the water table on nutrient dynamics and vegetation change in The publication costs for this article were funded by Scientific & Technical a wet grassland. Journal of Applied Ecology 1996, 33:576-588. Development Inc. 11. Willems JH, Peet RK, Bik L: Changes in chalk grassland structure and This article has been published as part of SpringerPlus Volume 2 Supplement species richness resulting from selective nutrient additions. Journal of 1, 2013: Proceedings of the 2010 International Conference on Combating Vegetation Science 1993, 4:203-212. Land Degradation in Agricultural Areas (ICCLD’10). The full contents of the 12. Wang GL, Liu GB, Xu MX: Effect of vegetation restoration on soil nutrient supplement are available online at http://www.springerplus.com/ changes in Zhifanggou watershed of loess hilly region. Bulletin of Soil supplements/2/S1. and Water Conservation 2001, 22(1):1-5. 13. Sangakkara UR, Frehner M, Nosberger J: Influence of soil moisture and Authors’ details fertilizer potassium on the vegetative growth of mungbean and Institute of Soil and Water Conservation, Northwest A&F University, Yangling, vowpea. J Agronomy and Crop Science 2001, 186:73-81. Shaanxi, China. Institute of Soil and Water Conservation, Chinese Academy of 14. Zha X, Tang K: Change about soil erosion and soil properties in Science and Ministry of Water Resource, Yangling, Shaanxi, China. reclaimed forestland of loesshilly region. Acta Geographica Sinica 2003, 58(3):464-469. Published: 11 December 2013 15. Fu BJ, Chen LD, Ma KM, Zhou HF, Wang J: The relationships between land use and soil conditions in the hilly area of the Loess Plateau in northern Shaanxi, China. Catena 2000, 39(1):69-78. References 16. Fu B, Wang J, Chen L, Qiu Y: The effects of land use on soil moisture 1. Arshad MA, Lowery B, Grossman B: Physical tests for monitoring soil variation in the Danangou catchment of the Loess Plateau, China. quality. In Methods for Assessing Soil Quality, SSSA Special Publications. Catena 2003, 54(1-2):197-213. Volume 49. Soil Science Society of America, Madison, WI, USA;Doran JW, 17. Stolte J, van Venrooij B, Zhang G, Trouwborst KO, Liu G, Ritsema CJ, Jones AJ 1996:123-141. Hessel R: Landuse induced spatial heterogeneity of soil hydraulic 2. Keddy PA: Effects of competition from shrubs on herbaceous wetland properties on the Loess Plateau in China. Catena 2003, 54(1-2):59-75. plants: a four-year field experiment. Canadian Journal of Forestry Research 18. Makeschin F: Effects of energy forestry on soils. Biomass and Bioenergy 1989, 67:708-716. 1994, 6(1-2):63-79. 3. Cambardella CA, Karlen DL: Spatial analysis of soil fertility parameters. 19. Paniagua A, Kammerbayuer J, Avedillo M, Andrews AM: Relationship of soil Precision Agric 1999, 1:5-14. characteristics to vegetation successions on a sequence of degraded 4. Critchley CNR, Chambers BJ, Fowbert JA, et al: Association between and rehabilitated soils in Honduras. Agriculture, Ecosystems and lowland grassland plant communities and soil properties[J]. Biological Environment 1999, 72:215-255. Conservation 2002, 105:199-215. Jiao et al. SpringerPlus 2013, 2(Suppl 1):S14 Page 6 of 6 http://www.springerplus.com/content/2/S1/S14 20. Chang QR, An SS, Liu J, Wang B, Wei Y: Study on benefits of recovering vegetation to prevent land deterioration on Loess Plateau. Journal of Soil Erosion and Soil and Water Conservation 1999, 5(4):6-9-44. 21. Yang WZ, Yu CZ: Region govern and evaluation in Loess Plateau[M]. Beijing: Science Press; 1992, 45-69. 22. Bhojvaid PP, Timmer VR: Soil dynamics in an age sequence of Prosopis juliflora planted for sodic soil restoration in India. Forest Ecology and Management 1998, 106(2-3):181-193. 23. Fang W, Peng SL: Development of species diversity in the restoration process of establishing a tropical manmade forest ecosystem in China. Forest Ecology and Management 1997, 99(1-2):185-196. doi:10.1186/2193-1801-2-S1-S14 Cite this article as: Jiao et al.: Soil nutrient assessment based on attribute recognition model in the Loess Plateau of China. SpringerPlus 2013 2(Suppl 1):S14. 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Soil nutrient assessment based on attribute recognition model in the Loess Plateau of China

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Springer Journals
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Copyright © 2013 by Jiao et al.; licensee Springer
Subject
Science, general; Science, general
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2193-1801
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10.1186/2193-1801-2-S1-S14
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Abstract

Soil fertility is important factors for growth and productivity of vegetation. The relationship between vegetation and soil fertility deserves attention due to its scientific importance and practical applications. However, the effects of soil fertility on vegetation development and succession are poorly documented. Here we study soil fertility in Yanhe watershed at northern Shaanxi on five different land uses, namely shrubland, farmland, natural grassland, woodland, and artificial grassland, and in soil under restoration for 5, 10, 15, 20, and 25. Attribute recognition model based on entropy weight was used to evaluate the soil fertility of typical region in the Loess Plateau of China, which contained 52 soil samples with 6 physical and chemical indexes, including soil organic matter, soil total nitrogen, total phosphorus, etc. The results show that (1) Land use has an obvious effect on soil bulk density, total porosity and capillary porosity of surface layers, but not significant in the subsurface layer; (2) SOM, N , total N and K are the most in shrubland and woodland while P and P in farmland, respectively; hydro avail total avail (3) Vegetation succession on eroded soil result in significant changing of soil fertility; and (4) Vegetation succession on eroded soil result in significant changing of soil fertility. Introduction degradation and supply of fuel and fodder in this area, and Soil fertility is important factors for growth and pro- reduced nutrients retention [14]. Deterioration of soil fer- ductivity of vegetation [1-3]. Vegetation structure, soil tility is important in vegetation restoration, especially for moisture and nutrients have very close relationship. converting agricultural land to reforested plantations or Different soil nutrients affect vegetation community grassland. This topic is also important in estimating the the size of the biomass, species composition and diver- role of natural vegetation recovery in soil rehabilitation of sity [4]. Soil nitrogen determines the productivity, biodi- the Loess Plateau, where little natural vegetation exists, versity and species invasive capacity of vegetation helping to guide current restoration of vegetation in west communities [5-7]. Phosphorus is a restrictive factor in a China. variety of soil types, and determines the size of vegetation Study of degradation processes attracts attention to productivity and change of species composition [8-12]. the influence of degradation on the human environment, Potassium also affects community biomass [10] and state but study of recovery processes is more important, pro- of vegetation water, and help to overcome soil moisture viding recommendations for eco-environmental recon- stress [13]. So, in vegetation restoration and reconstruc- struction or rehabilitation. Much research has been done recently on the influence on soil fertility properties tion, it is should be considered that soil properties of aban- doned farmland to assure that the ideal and realistic of vegetation recovery or different land-use patterns restoration goals [4]. However, over exploitation of exist- [15-17]. However, changes of soil fertility properties are ing vegetation further aggravates the problem of land still under study during the long-term recovery of vege- tation. Research into changes of soil fertility properties is considered necessary to understand the ecological * Correspondence: Jiaof11@126.com Institute of Soil and Water Conservation, Northwest A&F University, Yangling, consequences of vegetation recovery [18,19]. In the Shaanxi, China semiarid area of the Plateau, vegetation recovery or Full list of author information is available at the end of the article © 2013 Jiao et al.; licensee Springer This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Jiao et al. SpringerPlus 2013, 2(Suppl 1):S14 Page 2 of 6 http://www.springerplus.com/content/2/S1/S14 reconstruction is always limited by shortage of fertility. northern Shaanxi Province and had 25 years of compre- There is not much literature concerned with this parti- hensive management because one ecology station was cular issue, especially for long-term change of soil ferti- founded in this area (Figure 1). Of the area, 287 km of lity properties under natural re-vegetation in the Plateau length, 7687 km2 of the total area; 90% is hilly, 3% is [20]. The objective of the present study is to identify villages, rivers, and lakes; and only 7% is considered sui- changes in soil fertility in five different land uses includ- tablefor intensiveagriculture.The studyareahas a ing shrubland, natural grassland, artificial grassland, semi-arid climate characterized by heavy seasonal rain- farmland, and woodland, and changes in soil fertility after fall with periodic local flooding and drought; the average different restoration periods of plantations. We hypothe- annual rainfall at the experimental site is 497 mm sized that soil fertility properties are largely a function of (1970-2000, CV22%) with distinct wet and dry seasons. secondary succession re-growth. Other important factors, The rainy season starts in July and continues up to such as neighboring vegetation, climate change, and alti- October; the August rainfall accounts for 23% of the tude were not considered. The most popular natural grass- annual rainfall. The annual reference evapotranspiration land in the study area with vegetative chronosequence is is approximately 1000 mm. Most of the lands are also investigated to evaluate soil fertility on lands with dif- located at 900-1500 m altitude and are closely dissected ferent restoration times. and sharp-edged with steep and very steep slopes (the slopes are deep, 40%). The topography, soil type, soil Materials and methods and land-use patterns of Yanhe watershed are very typi- Study area cal in the Loess Plateau, Land-use types including: slop- The study area was located in Yanhe watershed of the ing land, terraces, orchards, woodland, shrubland, Loess Plateau at N 36°23′-37°17′and E 108°45′-110°28′ in natural grassland, wasteland and other types [21]. Figure 1 The location of study area on the Loess Plateau. Jiao et al. SpringerPlus 2013, 2(Suppl 1):S14 Page 3 of 6 http://www.springerplus.com/content/2/S1/S14 Study approach and sampling design properties can be measured by comparing sites of differ- The chronosequence method was used because of the ent ages. Five age series (5-, 10-, 15-, 20- and 25-year-old existence of similar conversion history in this area. The vegetation community) were found in the adjacent sites management was similar, with known periods of cultiva- of the study area, which have undergone light livestock tion climate, topography, and soil type. Soil samples were grazing in recent years. Within each community (5, 10, collected in August 2006. Soil samples were taken at 0-20 15, 20 and 25), five sites were selected as sampling (five cm depths. Composite samples of about 1 kg were col- replicates). Also, five nonvegetated lands in the vicinity of lected with 5 replicates at each sampling plot and then the planted sites (farmland) were chosen as a control for air-dried and sieved through 1 mm sieve. All measure- the chronosequence. ments were made at the State Key Laboratory of Soil Ero- sion and Dryland Farming on the Loess Plateau, China. Calculation of soil samples attribute measure and data The analytical methods for the soil samples were the analysis international standard methods as adopted and pub- Soil samples attribute measure is its status value in soil. It lished by the Institute of Soil Science, Chinese Academy is used that the second national soil survey classification of of Sciences (1978). Soil organic matter (SOM) was soil nutrient standards for the evaluation criteria, and a determined on the basis of oxidation with potassium standard matrix was built up based on the evaluation cri- dichromate in a heated oil bath. Total nitrogen (Ntotal) teria. Soil sample analysis of variance (ANOVA) and cor- was measured according to the semi micro Kjeldahl relation were carried out using the SPSS11.0 procedures method and hydrolysable nitrogen (Nhydro) by means for sites in different succession stages. Duncan’s test (at of the Alkali diffusion method. Total phosphorus (Pto- p < 0.05) was used to compare means of soil variables tal) was digested with perchloric acid and sulfuric acid when the results of ANOVA were significant at p < 0.05. and determined using colorimetry. Total potassium (Ktotal) was digested with hydrofluoric acid and per- Results and discussions chloric acid. Available phosphorus (Pavail) was extracted Soil fertility in different land uses with sodium bicarbonate and measured with colorime- Table 1 shows that, in different land use, changing try. Available potassium (Kavail) in soil was extracted SOM, Ntotal, Ptotal, Nhydro, Pavail and Kavail were sig- with ammonium acetate. nificant in the 0-20 cm layer at p < 0.05. Woodland A common approach in studies of soil rehabilitation in contains the highest all soil fertility indexes except relation to vegetative cover is to monitor plant and soil Pavail. Farmland contains the highest Ptotal (0.57%) and changes occurring along a vegetative chronosequence Pavail (2.06 mg/kg), and has a higher Kavail (60.2 mg/ developed on similar soils under similar climatic condi- kg). Natural grassland and Shrubland contain the high- tions [22]. This chronological approach has been widely est Kavail (70.0 mg/kg), and have higher SOM (8.11%) used in applied ecosystem research [23] and is considered and Ntotal (0.46%), respectively. While artificial grass- retrospective research because existing conditions were land has a lower contain in all soil fertility indexes. compared with known original conditions and treat- ments. The retrospective approach was adapted in this Weight of soil fertility index in different land uses study because of the availability of closely located vegeta- Table 2 shows that, in different land use, changing tion community established 5, 10, 15, 20 and 25 years weight of soil fertility index were significant in the ago on eroded soils with similar properties. These vegeta- 0-20 cm layer at p < 0.05. In the 0-20 cm layer, weight tion communities therefore provide a time gradient of of Nhydro was the highest in farmland, followed by grass occupancy on similar sites. Changes in soil SOM, Kavail, Pavail, Ntotal and Ptotal. Weight of SOM Table 1 Means and coefficient of variations of soil nutrient in different land-use patterns Land use SOM (%) N (%) P (%) N (mg/kg) P (mg/kg) K (mg/kg) total total hydro avail avail bc bc a cd a ab Farmland 6.87 (0.30) 0.44 (0.22) 0.57 (0.05) 26.5 (0.25) 2.06 (0.43) 60.2 (0.37) c c b d b b Artificial grassland 6.17 (0.32) 0.35 (0.22) 0.52 (0.03) 25.0 (0.12) 0.87 (0.64) 38.4 (0.15) b b b b b a Natural grassland 8.11 (0.24) 0.46 (0.32) 0.52 (0.12) 34.8 (0.23) 0.88 (0.13) 70.0 (0.27) a a a a b a Woodland 10.25 (0.19) 0.61 (0.15) 0.57 (0.06) 44.4 (0.19) 1.01 (0.37) 85.3 (0.47) bc b ab bc b a Shrubland 7.08 (0.27) 0.46 (0.27) 0.53 (0.08) 32.6 (0.27) 0.72 (0.34) 68.0 (0.39) Sig. of ANOVA 0.001 0.000 0.031 0.000 0.000 0.020 Means with the same letter in the same row are not significantly different at the 0.05 level (LSD). Data in the parentheses are coefficient of variation. Jiao et al. SpringerPlus 2013, 2(Suppl 1):S14 Page 4 of 6 http://www.springerplus.com/content/2/S1/S14 Table 2 Weight of soil nutrient index in different land use patterns Land use SOM N P N P K Sig. of ANOVA total total hydro avail avail b e f a d c Farmland 19.18 14.37 13.77 20.48 14.92 17.29 0.000 b bc cd de de a Artificial grassland 17.64 16.75 15.92 15.21 15.33 19.15 0.000 a c f b d e Natural grassland 21.09 17.87 11.53 19.17 15.72 14.62 0.000 c c bc a a ab Woodland 13.88 13.64 15.89 19.59 19.13 17.87 0.000 c c a b c c Shrubland 15.62 15.66 19.70 18.57 14.87 15.57 0.000 Means with the same letter in the same row are not significantly different at the 0.05 level (LSD). Data in the parentheses are coefficient of variation. was the highest in natural grassland, followed by Nhydro, Weight of soil fertility index in different restoration Ntotal, Pavail, Kavail and Ptotal. Compared with that in years farmland and natural grassland, weight of Kavail was the Figure 2 shows that, in different restoration years, chan- highest in artificial grassland, and weight of Nhydro and ging weight of soil fertility index was significant in the Pavail was the highest in Woodland, and weight of Ptotal 0-20 cm layer at p < 0.05. Abandoned early, the greater was the highest in Shrubland. In comparison, SOM, the weight and so are as follows: Pavail > Nhydro > Nhydro, Pavail and Kavail played an important role in SOM > Kavail > Ntotal > Ptotal. The difference between different land use. weights of soil fertility was significant at p < 0.05, the largest up 66.28% (Figure 2). With the increase of aban- doned years, the difference between weights of soil ferti- Soil fertility in different restoration years lity was reducing gradually. The largest differences Five replicated soil samples were collected from five between weights of soil fertility were 52.94%, 41.84%, sites with the same restoration time of 5, 10, 15, 20 and 30.97%, 23.04% and 11.01% in 5, 10, 15, 20 and 25 25 years, respectively. Also, five nonvegetated lands in the vicinity of the planted sites (farmland) were chosen years, respectively (Figure 2). The statistical results as controls for the chronosequence. After 5, 10, 15, 20 showed that: With the increase of abandoned years, and 25 years of restoration, SOM, Ntotal, Nhydro, Pavail affection of soil fertility on vegetation succession came and Kavail were significant in the 0-20 cm layer at p < into line gradually (Figure 2). 0.05 and except Ptotal, which was not significant at p > 0.05. Generally, vegetation succession resulted in a Conclusions change of soil fertility parameters in the eroded soils, Land use has an obvious effect on Soil fertility of surface significant decreases of soil fertility parameters (p < layer, but not significant in the subsurface layer. Shrub- 0.05) took place from beginning to 15-years of restora- land has higher soil fertility than other land uses. In tion, and significant increases (p < 0.05) from 15-years most cases, table land has low levels of soil fertility, but to 20-years of restoration, and significant decreases (p < after long period of cultivation, the land degrades year 0.05) from 20-years to 25-years of restoration. The sta- by year. Our results indicate that the establishment and tistical results showed that soil fertility and vegetation development of vegetation succession on eroded soil succession had significant interactions with all soil ferti- result in significant changing of soil fertility. With lity parameters except Ptotal (Table 3). increased plantation age, it is possible to recover soil Table 3 Means and standard deviations of soil nutrient in different restoration years Restoration time SOM(%) N (%) P (%) N (mg/kg) P (mg/kg) K (mg/kg) total total hydro avail avail de de d c c 25years 7.33 (1.31) 0.43 (0.07) 0.54(0.07) 29.3 (4.29) 0.70 (0.16) 64.9 (7.79) cde cde cd c c 20years 8.02 (1.47) 0.50 (0.15) 0.54(0.06) 31.9 (7.05) 0.67 (0.10) 66.0 (10.2) e e d c c 15years 5.93 (0.24) 0.36 (0.08) 0.54(0.06) 23.2 (2.68) 0.72 (0.10) 61.2 (17.2) e e d bc c 10years 5.53 (0.41) 0.37 (0.07) 0.54(0.04) 23.3 (4.62) 0.83 (0.18) 52.8 (20.5) de de d bc c 5years 6.62 (0.61) 0.43 (0.10) 0.53(0.03) 26.8 (5.99) 0.98 (0.17) 54.3 (27.4) de de d a c 0years 6.87 (0.30) 0.44 (0.22) 0.57(0.05) 26.5 (0.25) 2.06 (0.43) 60.2 (0.37) Sig. of ANOVA 0.000 0.000 0.627 0.000 0.000 0.003 Means with the same letter in the same row are not significantly different at the 0.05 level (LSD). Data in the parentheses are standard deviations. Jiao et al. SpringerPlus 2013, 2(Suppl 1):S14 Page 5 of 6 http://www.springerplus.com/content/2/S1/S14 Figure 2 Weight of soil fertility in different restoration years. 5. Chapin FS, Vitousek PM, Van Cleve K: The nature of nutrient limitation in fertility to a certain degree, and affection of soil fertility plant communities. American Naturalist 1986, 127:48-88. on vegetation succession came into line gradually. 6. Wedin DA, Tilman D: Influence of nitrogen loading and species composition on the carbon balance of grasslands. Science 1996, 274:1720-1723. Competing interests 7. Brooks ML: Effects of increased soil nitrogen on the dominance of alien The authors declare that they have no competing interests. annual plants in the Mojave Desert. Journal of Applied Ecology 2003, 40:344-353. Acknowledgements 8. 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SpringerPlus 2013, 2(Suppl 1):S14 Page 6 of 6 http://www.springerplus.com/content/2/S1/S14 20. Chang QR, An SS, Liu J, Wang B, Wei Y: Study on benefits of recovering vegetation to prevent land deterioration on Loess Plateau. Journal of Soil Erosion and Soil and Water Conservation 1999, 5(4):6-9-44. 21. Yang WZ, Yu CZ: Region govern and evaluation in Loess Plateau[M]. Beijing: Science Press; 1992, 45-69. 22. Bhojvaid PP, Timmer VR: Soil dynamics in an age sequence of Prosopis juliflora planted for sodic soil restoration in India. Forest Ecology and Management 1998, 106(2-3):181-193. 23. Fang W, Peng SL: Development of species diversity in the restoration process of establishing a tropical manmade forest ecosystem in China. Forest Ecology and Management 1997, 99(1-2):185-196. doi:10.1186/2193-1801-2-S1-S14 Cite this article as: Jiao et al.: Soil nutrient assessment based on attribute recognition model in the Loess Plateau of China. SpringerPlus 2013 2(Suppl 1):S14. 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