Effects Of Straw Returning Methods On Soil Organic Carbon And Available Nutrients

Crop straw is an important source of nutrients and organic matter in farmland soil.Straw returning management can effectively increase soil organic carbon and nutrient content.It is also an important way to improve soil environment and develop sustainable agriculture.In this study,a three-factor-five-level quadratic orthogonal rotation test was conducted in Northeast China.The straw length,amount and burying depth were defined as experimental factors.The primary objectives of this study were to investigate the effects of different straw return methods on soil organic carbon pool and available nutrient contents.At the same time,a comprehensive index of soil organic carbon and available nutrients was established using the Technique for Order Preference by Similarity to an Ideal Solution(TOPSIS)method.Based on this method,response surface methodology(RSM)was used to analyze the response of straw returning factors(straw length,returning volume,and depth)on soil organic carbon and available comprehensive index.This study was to explore the suitable straw returning mode for the modern agricultural machinery operation conditions in Northeast China,and provide scientific basis for effectively improving soil fertility.In the two years of straw returning to field,soil microbial biomass carbon,easily oxidizable organic carbon,and available potassium content were higher in soil layers of 10-15 cm and with a straw returning amount of 6800-8000 kg/hm~2.The content of particulate organic carbon in the soil layer of5-15 cm was significantly higher than that of 15-25 cm.The content of ammonium nitrogen and nitrate nitrogen in soil showed an increasing trend with the increase of straw returning amount.Besides,the ammonium nitrogen and nitrate nitrogen content of the treatment group with the straw returning amount of 6800-8000 kg/hm~2 was significantly higher than that of the treatment group with the straw returning amount of 2800 kg/hm~2.The value of soil carbon pool management index increased with the increase of straw returning amount and the shallow depth of straw buried soil.When the depth of straw is 5-10 cm,the amount of straw returned is 4800-8000 kg/hm~2,soil carbon pool management index was high.In addition,the soil carbon stock activity index,carbon stock index,and carbon stock management index were all higher in the straw returning treatment group when the straw burial depth was 5-15 cm,increased with the reduction of the depth of burial depth of the straw.The end period of straw returning to field,the response of straw returning factors to soil organic carbon and nutrients comprehensive index based on the response surface methodology showed that,different straw returning factors in this experiment have different response effects on soil organic carbon and available nutrient comprehensive indicator.The impacts of the three straw returning factors on soil organic carbon and available nutrient comprehensive index were as follows:straw returning depth>straw returning amount>straw returning length.Besides,there were different interactions between three straw returning factors on soil organic carbon and available nutrient comprehensive index.The results of the interactions of straw returning factors indicated that the content of soil organic carbon and available nutrient comprehensive index was positively correlated with straw returning amount,and negatively correlated with the straw returning depth and straw length.We concluded that a high soil carbon and nutrients comprehensive indicator was determined in the considered ranges in this research when the straw length,amount and burying depth were approximately 9-15 cm?4480-6700 kg/hm~2 and9-14 cm,respectively,which can be recommended as the suitable parameters for returning straw in this area.