Soil Organic Carbon And Nutrient Changes Under Different Land Use In Hilly Loess Plateau

Loess hilly areas since the implementation of returning farmland to forest project since the land use has undergone great changes.Loess hilly area not only land use patterns,terrain and soil texture is also very different.In all parts of the world,land use change is the main factor driving soil organic carbon,total nitrogen and total phosphorus change.However,as of now,soil organic carbon,total nitrogen,total phosphorus with land use changes have not been fully elucidated,especially in deep soil(> 100 cm).Therefore,we study the soil organic carbon in 0-100 cm soil layer under different land use types(farmland,jujube forest,7-year-old abandoned grassland and 30-year abandoned grassland)on the slope of the loess hilly region in China,Total nitrogen,total phosphorus.Quantify the contribution of deep soil organic carbon,total nitrogen and total phosphorus to the whole soil profile.In addition,in shallow soil(0-100 cm)we also analyzed the effects of soil texture(clay,granule and sand)and topographic factors(elevation,slope and aspect)on soil organic carbon,total nitrogen and total phosphorus.The differences of soil organic carbon,total nitrogen and total phosphorus between slope and channel were compared and analyzed.The main conclusions of this study are as follows:(1)In the whole small watershed,0-100 cm soil clay is about 14%,the grain is about 70%,and the sand is about 16%.The grain size,grain and clay content of 0-100 cm soil profile varied greatly in 30 years,and other land use types changed little.In the agricultural land,jujube forest,30 years abandoned grassland,7 years abandoned grassland and channel soil moisture with the soil depth increases.The mean values of soil water content of abandoned grassland,jujube forest and 7-year abandoned grassland,farmland and channel were 10.29%,11.66%,10.08%,11.43% and 11.34% respectively.0-20,20-40,40-60,60-80,80-100 cm soil soil average capacity were 1.26,1.29,1.31,1.35,1.34 g cm-3,the surface layer 0-40 cm average soil bulk density The(2)The land use type in the shallow section(0-100cm)significantly affected the distribution of soil organic carbon and the reserves in 0-20 cm soil layer,while 20-100 cm was not significant.The soil organic carbon content in the abandoned grassland was significantly higher than that in the abandoned grassland(P <0.05).Pearson correlation analysis showed that soil texture fraction and total nitrogen and soil organic carbon content were significantly or significantly correlated(P <0.05 or 0.01),but with the terrain factor showed a weak correlation.The variance analysis showed that there was no significant difference in the soil organic carbon content between the 0-40 cm soil slope and the channel soil,but there was a significant difference in soil organic carbon content between the slope and the channel under the 40 cm soil layer.In the deep section(0-1800cm),the soil organic carbon content and reserves decreased with the depth of soil layer,but the deep soil had higher soil organic carbon storage capacity.The accumulation of soil organic carbon at 100-1800 cm was 90.6,91.6,87.5 and 88.6% of the shallow 100 cm in the three land types,farmland,7-year abandoned grassland,30-year abandoned grassland and jujube forest.(3)The land use type in the shallow section(0-60cm)significantly affected the total nitrogen content of 0-20 cm soil layer,and 20-60 cm was not significant.While the total phosphorus content in the 0-60 cm soil layer were no significant difference.The soil total nitrogen content in the 0-60 cm soil layer decreased along the soil profile,while the total phosphorus increased with the depth of the soil.Soil soil organic carbon is the same as soil organic carbon,and total phosphorus is strongly related to soil texture(clay,grain and sand),and has a weak correlation with topographic conditions(aspect,slope and altitude).The variance analysis showed that there was a significant difference in the total nitrogen content of the slope and the channel soil in 0-40 cm soil layer at 0-60 cm soil profile,and there was no significant difference at 40-60 cm.There was a significant difference in soil total phosphorus content between 0 and 60 cm soil layers.The total soil total N reserves in the 100-1000 cm soil layer of the abandoned grassland,the abandoned grassland,the abandoned grassland and the jujube forest in the past 30 years accounted for 70.6,81.5,69.3 and 78.6% of the total 1000 cm soil profile,respectively.The total phosphorus reserves accounted for 40.6,,49.2,and 38.74% respectively.