| Purple soil slope farmland is an important farmland resources in the upper reaches of the Yangtze River,with high productivity and strong erosive characteristics.Most of the purple soil slope farmland has been reclaimed as cultivated land except for the tops of rocky slopes and hills in China.However,due to the shallow layer of purple soil,large soil bulk density,low aggregate content,and low organic matter content,under the influence of rainfall and man-made long-term farming activities,soil erosion on the purple soil slope farmland is serious,the erosion risk is gradually increased,and crop yield is low and unstable,seriously restricting the sustainable development of regional agriculture.Analyze the types of slope farmland obstacles and their effects on crop yields,study the effects of soil erosion and soil management measures on the quality and stability of cultivated layers,explore the characteristics of the suitability of cultivated layers on purple soil,and propose the method of regulating and controlling the reasonable cultivated layer of purple soil slope farmland can provide parameter basis for improving the quality of cultivated layer of slope farmland on purple soil and constructing a reasonable cultivated layer.This article takes the purple soil slope farmland as the research object,analyzes the formation process of the purple soil slope farmland and its influencing factors by referring to the data,and clarifies the obstacle types of the purple soil slope farmland;By comparing five different erosion degrees and two soil management measures,the soil aggregate composition,aggregate stability,and soil mechanical properties of the cultivated layer in a simulated community under field positioning shovel soil erosion were analyzed to analyze the changes in the stability of the arable land on slope farmland;Based on five different erosion levels and two soil management measures,the positioning shovel soil erosion simulation plots in the field were used to analyze the soil aggregate composition,aggregate stability,and soil mechanical properties change characteristics of the cultivated layer on the purple soil slope farmland;Analyze the characteristics of the soil material composition and structure,soil permeability,soil nutrients and crop yields of different erosion levels and management methods of the cultivated layer of slope farmland;Based on the analysis of the relationship between the cultivated layer structure characteristics,soil erosion,crop yield and soil attribute index of the slope farmland,and the characteristics of the suitability change of the soil attribute parameters of the slope farmland layer,according to the main obstacle types on the slope farmland,the quality control methods of the cultivated layer of slope farmland were proposed.The main conclusions are as follows:（1）Compared with the natural soil-forming process,human-induced farming activities lead to changes in soil physical and chemical characteristics and soil structure.A plow layer is formed in the cultivated layer.The cultivated layer can be divided into topsoil layer,plow layer,sedimentary layer,parent layer 4 levels;Deep ploughing can break the plow bottom layer formed by long-term shallow ploughing and accelerate the soil maturation of the cultivated layer.The soil under deep ploughing conditions is divided into three layers:active layer,stable layer and guarantee layer.Human-made farming activities can control and regulate the influence of natural factors on the soil formation process.During the cultivation process,the characteristics of the natural factors on the soil in the cultivated layer should be mastered.The cultivated layer is loose,and the core soil layer is more compact.There were significant differences in soil physical properties between purple soil slope farmland with different soil fertility grades.With the decrease of soil fertility grade,the slope of the plot was significantly larger,and the thickness of the effective soil layer of plot was significantly smaller.When the slope of the plot changed from 5.14°to 21.71°,the crop yield could be reduced by 44.83%.The lack of soil layer in the five-slope farmland was serious.However,the soil fertility attributes did not show significant differences.The soil organic matter,soil total nitrogen and cation exchange capacity of the first to fourth grade slope farmland in the same soil fertility grade were as follows:topsoil layer>subsoil layer>bottom soil layer.There was no significant difference between the topsoil layer and the subsoil layer in the fifth grade slope farmland.The soil quality index of each soil layer in the first and second grade slope farmland was between 0.434 and 0.528.The soil quality index of each soil layer of the same soil productivity grade was characterized by topsoil layer>subsoil layer>bottom soil layer;the soil physical properties had a more significant effect on the soil quality of low-yield slope farmland.The obstacle degree of the slope of the plot of the fifth-grade slope farmland was 80.73 times than that of the first-grade slope farmland.The purple soil slope farmland could be classified into three types,namely,III soil nutrient limitated type,IV effective soil layer thickness limitated type,and V field surface slope limitated type.When the soil physical property was the main obstacle feature,the cultivated layer structure was loose,the subsoil layer was seriously deficient,and the crop yield was 24.75%lower than that of the soil nutrient-restricted sloping farmland.（2）There is a large difference in the composition of soil aggregates in the cultivated layer of slope farmland under different erosion degrees.With the increase of the degree of erosion,the content of aggregates>5 mm showed a gradual decreasing trend,and the overall performance of DR0.25,MWD,and GMD was S-0>S-5>S-10>S-15>S-20.Under the erosion degree of S-00 and S-5,the MWD was significantly greater than that of S-10,S-15,and S-20（P<0.5）.With the increase of erosion degree,the overall content of water-stable aggregates>5 mm,WR0.25,MWD,and GMD showed S-0>S-5>S-10>S-15>S-20.The MWD of S-00 water-stable aggregates is the largest,between3.84-4.16 mm,and S-20is 47.94%-55.08%lower than that of S-0.The GMD of S-0water-stable aggregates is 0.78-0.99 mm,and S-2020 is 48.87%-50.85%lower than S-0.As the erosion intensifies,the destruction rate of the soil aggregates in the cultivated layer gradually increases,the stability of the cultivated layer gradually decreases,and the sloped farmland is more susceptible to erosion and destruction,resulting in poor quality of the cultivated layer.With the increase of the erosion degree,the soil shear strength of the cultivated layer increased first and then decreased,and the erosion degree of S-10increased to the maximum,between 8.71-9.56 kg/cm2.Soil compaction first decreases and then increases with the increase of erosion degree,and the erosion degree of S-55 is the smallest,between 8.97-10.63 kg/cm2.The overall penetration resistance of the cultivated layer of slope farmland under different erosion levels is S-5<S-0<S-10<S-15<S-20.The soil shear strength,compactness,and penetration resistance of 10-20 cm soil layer are all greater than 0-10 cm soil layer.The soil erodibility K value of purple soil slope farmland is between 0.04822-0.04839,and the soil erodibility gradually decreases with the increase of the degree of erosion.In general,the effect of BF treatment on the composition and stability of aggregates in soil was better than that in F treatment;the effect of F and BF treatment on soil water-stable aggregates in 0-10 cm soil layer was better than that in 10-20 cm soil layer.Under different management methods,the shear strength of the topsoil of slope farmland is CK,F and BF in descending order,and the soil compactness and penetration resistance are CK>F>BF.The interaction between the degree of soil erosion and the management method has a relatively small effect on the soil shear strength.The soil shear strength is mainly affected by the degree of erosion,and the interaction with the management method is not obvious.（3）The particle size distribution characteristics of the cultivated layer of slope farmland under different erosion degrees are significantly different.With the increase of the erosion degree,the sand grain content gradually increases,and the soil powder and clay content gradually decrease.Erosion increased from S-00 to S-20,soil sand content increased from 38.09%-42.38%to44.15%-46.35%,and soil clay content decreased from 12.62%-14.81%to 9.56%-11.01%.Coarse ossification is getting worse.With the intensification of erosion,the soil bulk density increased significantly,and the total soil porosity and capillary porosity gradually decreased.Compared with S-0,the soil bulk density under the erosion degree of S-15and S-20increased from 1.27-1.40 g/cm3respectively to 1.37-1.48 g/cm3 and 1.39-1.52 g/cm3.The initial infiltration rate,stable infiltration rate,average infiltration rate,and saturated hydraulic conductivity of the cultivated layer of slope farmland under different erosion levels are S-0>S-5>S-10>S-15>S-20（P<0.05）.Under the erosion degree of S-20,the initial infiltration rate of soil decreased the most,followed by the erosion degree of S-10,and S-2020 decreased by 43.12%-46.86%compared with S-15.The soil organic matter,cation exchange capacity,and pH value of the cultivated layer of slope farmland under different erosion levels are generally expressed as S-0>S-5>S-10>S-15>S-20.There are large differences in the content of sand,silt,clay,soil bulk density and porosity in the cultivated layer of slope farmland under different management methods.The soil sand content of the cultivated layer of the BF treatment downhill slope is significantly lower than that of the extensive management CK,the soil bulk density is also significantly reduced,the soil total porosity and capillary porosity are significantly increased,and the permeability is significantly enhanced,effectively improving the soil porosity of the cultivated layer,improve soil aeration and water permeability.Under different management methods,soil organic matter,CEC and pH values of BF treatment are the largest,followed by F treatment,and CK is the smallest,and the application of biochar+fertilizer can significantly increase the organic matter content and CEC value of the soil in the cultivated layer,and the effect is better than the single application of chemical fertilizer,and can improve the purple soil acidification status.The soil quality index of 0-20 cm cultivated layer varies greatly between different erosion levels and management methods.As the degree of erosion increases,the soil quality index of the cultivated layer gradually decreases,from S-00 erosion degree 0.332-0.414 to S-20erosion degree 0.221-0.280.Under BF treatment,the soil quality index of cultivated layer increased by 21.79%-27.24%,10.86%-15.94%compared with CK and F treatments;S-0,S-55 and S-1010 erosion degree of the soil quality of the cultivated layer all improved to the middle-grade cultivated layer（0.33≤SQI≤0.66）.The interaction between the degree of soil erosion and management methods of purple soil slope farmland has a significant effect on the soil quality index（P<0.05）.Under the same degree of erosion,the soil quality index showed no fertilization<single application of chemical fertilizers<application of biochar+chemical fertilizers,but the change range was relatively small.Relatively speaking,the effect of the degree of erosion on the soil quality index of the cultivated layer was more obvious.（4）Under conventional farming conditions,the overall structure of the cultivated layer on the uneroded slope farmland is that the cultivated layer（0-20 cm）is loose and the core soil layer（20-40 cm）is relatively compact.With the intensification of erosion,the soil bulk density of the cultivated layer and the core soil layer increases significantly,and the pore condition becomes significantly worse.The soil of the cultivated layer gradually compacts,which easily leads to soil compaction,which is not conducive to the growth of crops.Under the conditions of CK,F and BF,the degree of soil erosion and the mechanical composition of soil are extremely significantly related（P<0.01）;Under CK,F and BF treatments,the degree of soil erosion has a very significant correlation with the soil mechanical composition（P<0.01）;it has a very significant positive correlation with the soil bulk density（P<0.01）,and has a extremely significant negative correlation with total porosity and capillary porosity,initial infiltration rate,stable infiltration rate,average infiltration rate,and saturated hydraulic conductivity（P<0.01）;the degree of soil erosion has a significant negative correlation with the contents and stability of soil aggregates and water-stable aggregates（P<0.05）,the more serious the soil erosion of the cultivated layer,the worse the stability of the cultivated layer structure and water stability,the more easily the soil will be damaged by man-made mechanical disturbance and rainfall runoff erosion;the degree of soil erosion has a positive correlation with the soil penetration resistance and soil compactness,the more severe the soil erosion,the greater the soil penetration resistance,the greater the soil compaction,and the worse the cultivability;the degree of soil erosion has a significant negative correlation with the soil organic matter,cation exchange capacity,and pH value（P<0.05）.Under F treatment,the soil bulk density of S-00 and S-55 erosion levels were reduced to the appropriate range;BF treatment significantly reduced the soil bulk density,and the soil bulk density of each erosion degree fell to the appropriate value range.Under CK,F,and BF treatments,the soil saturated hydraulic conductivity was 53.52%-91.63%,45.37%-90.53%,36.12%-89.21%lower than the appropriate values,respectively.Under F treatment,the soil organic matter of S-00 erosion degree increased to the appropriate value range,9.30%higher than the appropriate value;Under the BF treatment,S-0,S-5,S-10,S-1515 soil erosion organic matter content of the cultivated layer increased to a suitable value range.BF treatment,the soil property index of the cultivated layer under the S-0erosion degree has good suitability,the sand content,penetration resistance,organic matter,and available phosphorus content are all within the appropriate value range.Cross-slope ridge cropping,no-tillage with concentrated soil,and biological moths can effectively improve the stability of the cultivated layer structure of the slope farmland,maintain the thickness of the cultivated layer of the slope farmland,and reduce soil loss of the slope farmland.In particular,no-tillage on poly soil can significantly increase the thickness of the cultivated layer,accelerate the maturation of deep soil,and increase crop yield.The application of biochar can improve the soil pore condition,significantly increase the soil nutrient content of the cultivated layer,and the soil acidification phenomenon has also been significantly improved.The plant hedge can significantly reduce the slope of the slope,make the slope of the sloping field naturally cascade,and shorten the slope length.Planting a hedge for 4 years can slow down the slope by 8-12°.The effect is remarkable,and it can gradually become a gentle slope or horizontal terrace.Therefore,the effective soil layer thickness-limited slope farmland can be combined with no-till soil and biochar to improve the quality of the farmland and increase crop yields;Nutrient-restricted slope farmland can adopt the combination of horizontal slope ridge farming and biochar application to reduce soil erosion on slope farmland,increase soil nutrient content in the plow layer,and increase crop yield;Field slope-restricted slope farmland can reduce slope by planting hedges and reduce soil loss in the cultivated layer. |
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