Stability Of Soil Structure And Its Effect On Soil Anti-erodibility In Topsoil Of Sloping Farmland Of Purple Soil Region

Sloping farmland is an important component of China's arable land resources.However,due to its regional characteristics as a steep slope,sloping farmland often have thin soil tillage layers,low structural stability,and high soil detachment rate..Soil anti-erodibility on sloping farmland is strongly affected by the stability of the soil structure.Thus,a better understanding of soil structural stability and its effects on soil anti-erodibility of the sloping farmland in the purple soil region of China is of great significance in the reduction of soil erosion and to ensure regional food security.A field investigation combined with laboratory analysis was conducted in the purple soil region of Sichuan province to investigate the characteristics of soil structural stability in the topsoil and subsoil and soil anti-erodibility in the typical sloping farmland with three different slope gradients[gentle slope?0°to5°?;middle slope?5°to 15°?;steep slope?15°to 25°?].The relationship between soil structural stability and soil anti-erodibilitywas also revealed..The main results of this study are as follows:?1?The differences in soil structural stability with varying soil depth and gradient on sloping farmland were studied.Results showed that sloping farmland in the purple soil region has a thin soil depth,with the topsoil layer being only about 10 cm.More importantly,the differences in soil aggregate stability,soil organic matter?SOM?and pH at different depths were 0–10 cm>10–20 cm while soil clay content,soil compaction?SC?,soil shear stress?SHS?were 0–10 cm<10–20 cm.The characteristics of soil aggregate stability,soil mechanical properties,and soil biological properties in the same soil layer with different slope were middle slope>gentle slope>steep slope.?2?The four principle components that affected soil structural stability and one comprehensive principle component model in the topsoil was established.The principle components and their variance contribution include water stability of soil structure?P₁,47.7%?,mechanical stability of soil structure?P₂,16.2%?,biological stability of soil structure?P₃,15.2%?,and gradient?P₄,9.3%?.The comprehensive principle component?P₀?model calculated by P₁,P₂,P₃,and P₄ were P₀=0.540P₁+0.183P₂+0.172P₃+0.105P₄.Soil structural stability index was a suitable indicator that can be used to describe the stability of the soil structure on sloping farmland in the hilly region of Sichuan province.?3?The ranking system of the soil structural stability in the topsoil of the sloping farmland has been discussed.The structural stability of the topsoil in the study area can be divided into four grades through cluster analysis.From the highest to the lowest stability,the grades were A?2.98 to 1.50?,B?1.50 to0.28?,C?0.28 to-0.95?,and D?-0.95 to-2.18?while structural stability with grades A and B can be regarded as an optimum tillage layer in the study area.?4?The relationship between soil structural stability and soil anti-erodibility was elucidated.A significant correlation between soil anti-scourability?y?and soil structural stability index?x?can be observed:y=0.295x+1.801?R²=0.683,n=21?.Thus,soil structure can have a significant effect on soil anti-erodibility,and this anti-erodibility increased with the enhancement of soil structural stability.In conclusion,soil structural stability index was a comprehensive indicator to determine soil anti-erodibility and the stability of soil structure in the topsoil of the sloping farmland in the hilly region of Sichuan.Therefore,soil structural stability could be improved further and soil anti-erodibility can be enhanced to protect arable land resources and prevent soil loss in the hilly region of Sichuan.?5?The characteristics of soil anti-erodibility on sloping farmland in the hilly region of Sichuan were revealed.The soil aggregate disintegration rate in the topsoil?0 to 10cm?was 47%to 76%while soil anti-scourability index was 0.94 min·g^-1 to 3.33 min·g^-1.The significant correlation between soil aggregate disintegration rate and soil anti-scourability and soil anti-erodibility on different sloping farmland was as follows:gentle slope>middle slope>steep slope.The overall anti-erodibility on sloping farmland in the hilly region of Sichuan was moderate compared with the different soil types:loess soil in northwest<purple soil in Sichuan<black soil in the northeast.?6?Five soil factors which can be used for describing soil structure was selected from four different principle components:mean weight diameter by wet-sieving?MWDW?,soil organic matter?SOM?,soil compaction?SC?,soil microbial biomass nitrogen?SMN?,and slope?SLOPE?.Furthermore,combined with the ranking system of the soil structural stability,we defined the interval for these indicators,as MWDW:1.93±0.07,SOM:18.22±1.3g·kg^-1,SC:625.17±64.54 kPa,SMN:48.07±4.88mg·kg^-1;and SLOPE:5.63±0.6°,which can be used as reference values in the topsoil with fine structure on sloping farmland.