Optimization Of Maize Straw Return Measures Based On Soil Erosion Resistance Regulation

Soil erosion is a serious problem in northern rocky mountainous areas with mixed soil and rocks on the surface and thin soil layers.Soil erosion resistance is an intrinsic factor affecting soil erosion,which mainly includes soil erodibility（K_d）and soil critical shear（τ_c）.Maize straw crushing and returning to the field is a widely used agricultural practice that can change the physicochemical properties of soil and affect soil erosion resistance,but the mechanism of its influence is not clear.In this study,a 21-month straw return experiment was conducted on a sloping field with brown loam soil in a northern rocky mountainous area.An orthogonal design was used,applying a L₉（3³）orthogonal table to three factors and three levels of straw crushing length（6,9,12 cm）,straw return depth（9,12,15 cm）,and straw return volume(1000,4500,8000kg ha^-1),resulting in nine treatments.In order to investigate the effect of continuous straw return over many years on soil physicochemical properties and erosion resistance,we selected 0,3-4,5-6,7-8,9-10,15,and 20 years of continuous straw return treatments for in situ sampling and analysis in the field.We used a JET soil erosion resistance tester to measure K_dandτ_cand also measured soil physicochemical properties and residual straw.Using correlation analysis,general linear analysis,and partial least squares regression,we analyzed the effects and mechanisms of maize straw crushing on soil erosion resistance.The main results were as follows:（1）The effect of straw crushing and returning on K_dandτ_cshowed differences.Compared withτ_c,K_dwas more sensitive to straw returning,with an average coefficient of variation of 0.40,whileτ_chad a smaller average coefficient of variation of 0.20.Both K_dandτ_cshowed a moderate degree of variation.With the increase in straw decomposition time,τ_cfirst increased and then decreased,while K_dshowed a pattern of first decreasing and then increasing.In the long-term straw returning experiment,there was no clear pattern of change inτ_cand K_d.Compared with the treatment without straw returning,the decrease in K_dunder the straw returning treatments for 3-4years,5-6 years,7-8 years,15 years,and 20 years ranged from 17%to 73%,and the increase inτ_cunder the continuous straw returning treatments for 3-4 years,5-6 years,and 7-8 years ranged from2%to 21%.（2）The key factors and soil physicochemical properties affecting K_dandτ_cwere different under the influence of straw crushing and returning.In terms of soil physicochemical properties,K_dwas mainly influenced by fulvic acid,humic acid,humus,Ca²⁺,Mg²⁺,and other factors,indicating that K_dwas mainly affected by particle aggregation within the soil.τ_cwas mainly affected by soil water content,initial soil water content,soil capillary porosity,and soil aeration porosity,indicating thatτ_cwas mainly controlled by the pore space between soil aggregates.K_dwas mainly affected by the length of straw crushing and the depth of straw returning（P<0.05）,with a contribution rate of 19%-42%.With the passage of time,the positive correlation between the two and K_dbecame negative.τ_chad a significant positive correlation with straw return depth（contribution rate of 38%）and straw return amount（contribution rate of 54%）（P<0.05）.In addition,after straw returning,early soil erosion resistance was mainly affected by soil physical properties,while later stages were mainly affected by the combined effect of residual straw and soil physicochemical properties.（3）Different optimization strategies for straw returning measures based on K_d,τ_c,and soil erosion resistance control were identified.The best way to reduce K_dwas to use straw with a length of 6 cm,a straw returning depth of 12 cm,and a straw returning amount of 4500 kg ha^-1.The best way to increaseτ_cwas to use straw with a length of 9 cm,a straw returning depth of 15cm,and a straw returning amount of 8000 kg ha^-1.The best way to enhance soil erosion resistance was to use straw with a crushing length of 12 cm,a straw returning depth of 15 cm,and a straw returning amount of 1000 kg ha^-1,followed by using straw with a crushing length of 6 cm,a straw returning depth of 15 cm,and a straw returning amount of 8000 kg ha^-1.In the long-term straw returning experiment,continuous straw returning for 20 years was the most effective way to reduce K_d,while straw returning for 3-4 years was the most effective way to increaseτ_c.Within 21 months of straw returning,the best way to enhance soil erosion resistance was to return straw for 9 months.The best way to enhance soil erosion resistance within 3-20 years of straw returning was to return straw for 20 years,followed by 5-6 years and 3-4 years of straw returning.