Study On The Restoration Effect Of Cultivated-layer Soil Quality And Its Response To Environmental Factors On Purple Soil Sloping Farmland

Purple soil(Entisols)sloping farmland is not only an important cultivated land resource in Southwest China but also the source of soil and water loss in the Three Gorges Reservoir Area.Its cultivated-layer soil quality is characterized by severe erosion degradation and low and unstable crop yields.Soil erosion,soil nutrient loss,and crop yield constraints caused by rainfall and runoff erosion are the main factors threatening the sustainable development of cultivated land and agricultural ecosystems in purple hilly areas.Soil management measures can effectively improve soil structure,enhance soil water retention capacity and improve soil fertility,thereby achieving improved farmland productivity and ensuring food security.It is of great scientific significance and application value for erosion degradation restoration and crop yield increase on sloping farmland to study the restoration effects of physical and chemical properties of cultivated-layers and the response characteristics of cultivated-layer quality to environmental factors under the dual driving factors:erosion degree and management measures.In this paper,the cultivated-layer soil on a typical slope in purple hilly areas was used as the research object,and an artificial shovel test(topsoil movement method)plot was established with five erosion levels(S0,S5,S10,S15,S20)and three soil management measures(no fertilizer CK,chemical fertilizer F,and biochar+chemical fertilizer BF).The specific objectives of this study are:based on plot-scale sloping farmland erosion/management orientation experiments,to analyze the restoration effects of management measures on the physical and chemical properties of cultivated layer with different erosion degrees and their interannual variation characteristics;based on the field survey of sloping farmland cultivated-layer soil at a small watershed scale,to analyze the change characteristics and obstacle factors of the cultivated-layer quality,to quantitatively evaluate the impact of environmental factors such as altitude,slope,effective soil layer thickness,and slope position through evaluation models such as principal component analysis and constrained ordering,and to analyze the response characteristics of cultivated-layer quality to the interaction of environmental factors through the response surface model.The main conclusions are as follows:(1)Soil management measures significantly restored the physical properties of eroded cultivated-layer,with significant differences in the response of cultivated-layer soil bulk density,porosity,and soil infiltration rate to management measures,and were not sensitive to the interaction with erosion degrees.With BF measures,the sand content of 0～10cm and 10～20cm layers significantly decreased by 35.27 and 12.32%compared to F,the clay content significantly increased by 44.05 and 53.27%,the bulk density significantly decreased by 6.95 and 7.00%,and the porosity significantly increased by 7.79 and 8.56%.After 4 years of consecutive management,with the F and BF measures,the sand content in the cultivated layer has decreased by 5.56 and 10.52%annually,the silt content has increased by 3.82 and 3.01%annually,and the clay content has increased by 3.08 and 13.60%annually.Moreover,the improvement effect on the texture of the10～20 cm layer in the profile is better.The soil bulk density of the cultivated layer increased by 0.71and decreased by 1.09%annually,soil porosity decreases by 0.68%and increases by 1.29%annually,and biochar has a better effect on improving the bulk density and porosity of the profile of 30～40 cm.The initial infiltration rate of the cultivated layer increased by 0.92 and decreased by 5.26%per year,the stable infiltration rate increased by 0.43 and decreased by 4.25%per year,and the saturated hydraulic conductivity increased by 3.46 and decreased by 1.79%per year,respectively.The topsoil infiltration rate is higher,and the biochar inhibits the infiltration process of the profile.The interaction between soil erosion degrees and management measures has a relatively small impact on cultivated-layer bulk density,porosity,initial infiltration rate,and stable infiltration rate.The regression model determination coefficients R~2 are 94.71,95.13,64.69,and 70.49%,respectively.Physical indicators are more sensitive to soil management measures.(2)Soil management measures significantly restored the chemical properties of eroded cultivated-layer,with significant differences in the response of cultivated-layer SOC,p H,and CEC to management measures,and were not sensitive to the interaction with erosion degrees.With BF measures,SOC in 0～10cm and 10～20cm layers significantly increased by 30.96 and23.20%compared to F,and CEC significantly increased by 16.71 and 16.28%.BF measures can effectively improve the p H of the eroded cultivated layer soil.With CK and F measures,the average p H of the cultivated layer is 5.01 and 5.72,respectively,which are slightly acidic,while with BF measures,the average p H is 7.38,which is slightly neutral.After 4 years of consecutive management,with F and BF measures,the average annual increase of SOC in the cultivated layer was 3.12 and9.24%,while the average annual increase of p H was basically unchanged and 0.41 units,and both of them had the best effect on improving the nutrient index of 0～10cm of the profile,but with CK,the average annual loss of cultivated layer SOC is 12.18%,and the average annual decrease of p H is0.18 units.The interaction between soil erosion degrees and management measures has a relatively small impact on cultivated-layer SOC,p H,and CEC.The regression model determination coefficients R~2 are 98.53,98.97,and 92.90%,respectively.Nutrient indicators are more sensitive to soil management measures.(3)Soil management measures have a significant impact on the profile distribution of soil physical and chemical properties in sloping farmland,and the restoration effect of biochar+fertilizer on surface is better than that of other layers in the profile.With BF measures,the clay content in the full profile and the cultivated-layer profile increased by 35.11%and 47.78%on average compared to F,while the sand content decreased by 18.71%and 18.42%;the bulk density of the full profile and the cultivated-layer profile decreased by 4.77%and 7.01%compared to F,respectively,and the porosity increased by 5.73%and 8.19%;the initial infiltration rate,stable infiltration rate,and average infiltration rate of the full profile decreased by 36.08,28.95,and18.18%compared to F,respectively,while the saturated hydraulic conductivity basically remained unchanged,the above indicators decreased by 27.72,26.29,20.42,and 8.79%in the cultivated-layer profile.The vertical distribution of SOC and CEC is characterized by"surface aggregation",which is characterized by surface layer>subsoil layer.The change range of nutrients in the bottom layer is small,and the nutrient accumulation effect is weakened.BF measures significantly increased the profile SOC,p H,and CEC,with the best effect(+1.5 times)for SOC at 0-10 cm,and 0.94～1.25times for other layers of the profile.Soil p H at 0～10cm had the best improvement effect(+2.46units),while the other layers increased by 0.96～2.28 units.Soil CEC at 0～10cm had the best lifting effect(+41.12%),while other layers increased by 13.16～40.90%.(4)The cultivated-layer soil quality and soil attribute indicators of purple soil sloping farmland at small watershed scale showed a significant level of difference,and the cultivated-layer quality responded significantly to environmental factors.The thickness and bulk density of cultivated-layer are within a suitable range,and the texture is sandy silt soil.The soil infiltration performance is weak.The soil nutrient content occurs at a lower middle level in the cultivated-layer,and the soil attribute indicators are generally medium to low sensitivity(CV<100%).The average value of the cultivated-layer soil quality index(CLSQI)of sloping farmland is 0.450(CV15.98%),and the soil quality is at a medium to low level.From the perspective of topographic factors,there is a significant difference in CLSQI between low altitude and high altitude.The distribution characteristics of CLSQI at different slope positions are downslope(0.461)>middle slope(0.448)>upslope(0.440).The obstacle factors of CLSQ in sloping farmland are organic matter,total nitrogen,and bulk density,all of which belong to moderate obstacles.The main obstacle factors on uphill slopes are total porosity,sand,organic matter,and total nitrogen,while on the middle and lower slopes are bulk density,organic matter,and total nitrogen.According to the partial redundancy analysis results,the order of importance of environmental factors on CLSQ is EST(6.8%)>SP(3.1%)>AL(1.6%)>SL(1.1%),with only EST and SP reaching significant levels,and the main influencing factors causing spatial variability of CLSQ are EST and SP.From the response surface analysis results,it can be seen that the interaction between effective soil layer thickness and slope position,as well as the interaction between effective soil layer thickness and slope have a relatively large impact on the CLSQ,and the CLSQ is more sensitive to the effective soil layer thickness.