| The karst area of Southwest China is the area with the largest rocky desertification and the most typical karst development in the world.Broken surface,exposed bedrock,barren soil and serious decline in land productivity have become the most typical characteristics of this area.However,the karst area in Southwest China is very densely populated,and agricultural planting is widely developed.At the same time,slope farmland is the main carrier of agricultural production in this area.Frequent farming and unreasonable land use have exacerbated the soil and water loss of regional slope farmland.Soil erosion caused by rocky desertification and human activities is becoming more and more serious,swallowing the living and development space of local residents,especially in Guizhou,where the contradiction between man and land is very acute.In this study,Jinlan demonstration area in Qianxi City,Guizhou Province was taken as the research area,and the related experiments of soil and water conservation function of straw mulching tillage measures on sloping farmland were carried out from 2018 to 2021.A total of 6 straw mulching planting communities with a specification of3 m（width）×12 m（long）were set with a slope of 15°.Corn is planted in the community,and the planting specifications are roughly the same as those of local farmers.The six planting plots include corn monoculture+straw mulching（SM0—SM5,0,1111,2222,3889,5556,6944 kg/hm~2）,of which SM0 is the control group（CK）.Based on the 4-year observation data of soil moisture and nutrients and runoff and sediment yield in the soil tillage layer,this paper discusses the impact of straw mulching on the soil environment and runoff and sediment yield on the slope,in order to control soil and water loss in the karst area of Southwest China,Provide theoretical support for soil quality improvement.The results showed that:（1）With the increase of straw mulching,the soil moisture content showed an upward trend.Among them,SM4 and SM5 had significant moisture conservation effects.From 2018 to 2021,their moisture conservation effects were significantly better than CK（P<0.05）,but there was no significant difference between them（P>0.05）.（2）With the increase of straw mulching,the contents of soil SOC,TN,TP and available nutrients（AN,AP,AK）also increased except TK,especially SM4 and SM5,which were significantly higher than the CK（P<0.05）,but there was no significant difference between them（P>0.05）;For TK,it showed a decreasing trend with the increase of straw mulching.With the increase of straw mulching time,the contents of SOC,TN,TP and available nutrients also increased.（3）Under the condition of high straw mulching（SM4,SM5）,except N:P,the stoichiometric ratios of soil nutrient elements in four years were significantly higher than those in the CK（P<0.05）,but there was no significant difference between SM4 and SM5（P>0.05）;Under the condition of straw mulching,the soil C:N and C:P were low,which accelerated the mineralization and decomposition of soil organic matter,and also showed that the effectiveness of P was high;The lower N:P in the soil layer indicates that the crop growth in each plot is limited by N,and the lower C:P and N:P indicate that the soil nutrients in this area are in a state of lack of N and rich P.（4）Under different rainfall levels,straw mulching had better soil and water conservation effect,and the total amount of runoff and sediment decreased with the increase of mulching amount.The runoff and sediment yield of each mulching treatment from seedling stage to jointing stage was higher than that from jointing stage to heading stage and heading stage to maturity stage,and the runoff and sediment yield of each mulching treatment at each stage was lower than that of the control.Compared with the control,the average annual runoff depth of each mulching treatment decreased by 29.82%—59.60%,and the soil erosion modulus decreased by 44.68%—88.01%.With the increase of straw mulching rate,the runoff and sediment yield decreased exponentially,but when the straw mulching reached 5556 kg/hm~2 and continued to increase the straw to 6944 kg/hm~2,the runoff and sediment yield did not change significantly（P>0.05）.（5）Based on the comprehensive score of soil fertility,regression analysis of runoff and sediment yield and difference analysis results of slope farmland under straw mulch,combined with the functional benefits of slope soil and water conservation under different straw mulch and the economic range that local farmers can bear,it is recommended to cover about 6000 kg/hm~2 of straw on karst slope farmland in Southwest China,and add potassium fertilizer appropriately to maintain soil potassium balance,to promote the restoration of farmland ecosystem,so as to achieve better soil and water conservation and soil fertilization.The research results can provide reference for the comprehensive prevention and control of soil and water loss,the theoretical research and practice of straw returning to the field and the correction of relevant soil erosion models in southwest karst area. |
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