Soil And Water Loss Control Effect Of Sloping Farmland Mulching Measures In Northwest Guizhou

The area ratio of sloping farmland in karst area of Southwest China is large,which is the main source of soil erosion.The special karst environment makes the problem of regional engineering water shortage prominent,coupled with extensive farming methods,resulting in regional sloping farmland soil is relatively poor.In this paper,taking the sloping farmland agronomic mulching measures in Northwest Guizhou as the research object,taking the method of field runoff plot positioning,we continuously observed the impact of agronomic mulching measures on sloping farmland soil environment and soil erosion from 2018 to 2020.Agronomic mulching measures mainly included straw mulching（SM）,biochar mulching（BM）,and grain and grass intercropping（GI）.Based on mulching application rate,straw mulching was set with SM1—SM5,biochar mulching was set with BM1—BM4,and grain and grass intercropping was set with alfalfa（AI）,chicory（CI）and ryegrass（RI）intercropping with maize according to forage species,and maize monoculture mode without mulch was set as control（CK）,which were13 treatments.Based on the three-year observation data of soil moisture,nutrients（organic matter,SOM;total nitrogen,TN;total phosphorus,TP;total potassium,TK;available nitrogen,AN;available phosphorus,AP;available potassium,AK）,runoff and sediment yield and soil mechanics,this paper focused on the impact and mechanism of agronomic mulching measures on soil moisture and ferterity environment and runoff and sediment yield in Northwest Guizhou,the results showed that:（1）With the increase of straw mulching application rate,the effect of soil moisture conservation showed an upward trend,soil moisture content of SM4 and SM5 was significantly higer than trhat of CK（P<0.05）,however,through the analysis of three years of soil moisture observation records,it was found that,the relationship between soil moisture content and straw mulching application rate was not a simple linear function,but it was more consistent with the change trend of exponential,quartic polynomial and logistic function model;With the increase of biochar mulching,the soil moisture conservation effect was improving,but it was not significant compared with CK,especially in2018;the effect of soil moisture conservation of grain and grass intercropping was not obvious,the effect of soil moisture conservation of AI was better than CK,CI and RI,but there was no significant difference（P>0.05）;The average soil moisture conservation effect of straw mulching（SM）was significantly better than that of biochar mulching（BM）and grain and grass intercropping（GI）（P<0.05）.（2）The contents of SOM,TN,TP and available nutrients were significantly increased with the increase of straw and biochar mulching application rate（P<0.05）,but different from biochar mulching,soil TK did not increase with the continuous increase of straw mulching application rate,but showed a trend of first increase and then decrease;under AI treatment,the contents of TN and AN in soil were significantly higher than those of CK,CI and RI,with an average increase of 79.34%and 66.72%respectively compared to CK in three years.In terms of the effects of different mulching measures on soil nutrients,the content of soil organic matter under biochar mulching（BM）was significantly higher than that under straw mulching（SM）and grain and grass intercropping（GI）.The soil TK under straw mulching was the lowest,which was significantly lower than that under biochar mulching and grain and grass intercropping.The content of TN and AN in grain and grass intercropping was significantly higher than that in straw and biochar mulching（P<0.05）.（3）Under the conditions of straw mulching,biochar mulching and intercropping of grain and grass,the peak of runoff and sediment in sloping farmland was concentrated in maize seedling stage.The control effect of straw mulching on runoff and sediment in maize seedling stage was significant,especially in SM4 and SM5 treatments,from 2018 to2020,compared with CK,the runoff under SM4 and SM5 decreased by72.14%,63.89%;65.32%,62.30%;87.34%,85.92%,and the sediment yield decreased by 87.68%,79.52%;93.80%,90.00%;97.74%,97.20%.In the three years,the runoff and sediment control effect of straw mulching at maize ear and flowering and grain stage was not significant;the control effect of biochar mulching on soil and water loss was not significant in maize seedling stage,with the advance of maize growth period,the effect of biochar mulching on runoff and sediment control gradually improved,especially for BM5 treatment at maize ear stage.Compared with CK,the runoff and sediment yield under BM5 decreased by 70.14%,33.34%;59.41%,77.54%,and 86.67%,76.50%at maize ear stage from 2018～2020,and the sediment reduction effect was better than that of runoff reduction;The effective prevention and control of soil and water loss by intercropping with grain and grass was mainly concentrated in the maize flowering stage,and the effect of CI treatment on reducing runoff and sediment was particularly significant in this stage,the runoff and sediment yield under CI in 2019 and 2020 was significantly lower than that of CK（P>0.05）,the runoff reduction rate was 59.39%and62.85%,and the sediment reduction rate was 84.04%and 91.41%,respectively,the effect of sediment reduction was better than that of runoff reduction;the runoff and sediment amount of sloping farmland had significant multivariate power function relationship with rainfall（P）and maximum 30 min rainfall intensity(I₃₀).In general,the regulation effect of straw mulching on runoff and sediment was better than biochar mulching and grain and grass intercropping from 2018 to 2020.（4）Under the condition of straw and biothar mulching,the soil internal friction angleφ,cohesion c and shear displacementΔl had no significant difference with CK,and there were also no significant differences among the straw mulching treatments（P>0.05）.The soil compactness decreased with the increase of straw and biothar mulching application rate;grain and grass intercropping had significant effects on soil internal friction angleφand cohesion c,Under AI,CI and RI treatments,soil internal friction angleφand cohesion c were significantly higher than those of CK（P<0.05）,especially by RI,its soil internal friction angleφand cohesion c were significantly higher than those of AI and CI（P<0.05）,and the results showed that the shear strength under RI was higher than CK,AI and CI under the vertical normal stress of 100,200,300 and 400 k Pa,and the soil compaction was large under the condition of grain and grass intercropping.Under different mulching measures,soil internal friction angleφand cohesion c were significantly positively correlated,while cohesion c was significantly negatively correlated with sediment yield modulus;as far as the influence of agronomic mulching measures on soil shear strength was concerned,the effect of grain and grass intercropping was the most significant.