Effects Of Straw Returning To The Field On Nitrogen And COD Loss In Farmland Runoff And Carbon,Nitrogen In Soil Aggregates

Returning straw to the field is one of the valid management steps for improving soil quality and increasing crop yield in agricultural ecosystems.Based on the field positioning trial of straw returning for 8a,the influences of straw returning and different fertilization methods on the runoff nitrogen and COD drain,soil aggregate distribution characteristics,aggregate carbon and nitrogen component distribution patterns,and crop yield in the Chaohu Lake Basin were investigated.The experiment were set up six disposes,no straw returning+no fertilization（CK）,conventional fertilization（F）,straw returning+conventional fertilization（SF1）,straw returning+80%conventional fertilization（SF2）,optimized fertilization（NPK）,and straw returning+80%optimal fertilization（NPK-）,in order to provide theoretical basis for effectively controlling nutrient loss,improving soil fertility,and crop yield in the farmland of Chaohu Lake region.The main research results are as follows:（1）Under the oil rice rotation model,the link of straw returning and chemical fertilizer significantly decreased the mass concentration of nitrogen（TN,NH₄⁺-N,and NO₃^--N）in farmland runoff,and the mass concentration of nitrogen in NPK-was the lowest.Compared with conventional fertilization,the mass concentration of TN in farmland runoff treated with SF1 and NPK significantly decreased by 10.29%～15.83%and5.16%～8.61%（P<0.05）in rape and rice seasons respectively;The mass concentrations of NH₄⁺-N and NO₃^--N decreased by 22.72%～26.39%and 10.17～15.96%（P<0.05）in the rape season respectively,while decreased by 33.80%～36.08%and 5.11%～12.38%（P<0.05）in the rice season,respectively;The mass concentration of COD treated with SF1 increased by 10.31%～15.14%compared to F in the fourth quarter.（2）Compared to traditional fertilization,straw returning to field decreased the risk of nitrogen loss and increased the amount of COD loss.However,straw returning to field and reduced fertilization can reduce the risk of COD emission and alleviate the pollution of surrounding water bodies.The amount of TN loss from farmland runoff treated with SF1and NPK significantly decreased by 11.30%～22.97%and 20.28%～24.70%（P<0.05）in rape and rice seasons,respectively,compared to F treatment;The mass concentrations of NH₄⁺-N and NO₃^--N decreased by 30.30%～35.58%and 18.81%～24.96%in the rape season,and by 7.24%～19.13%and 2.81%～14.11%（P<0.05）in the rice season,respectively;The amount of COD loss from SF1 compared to F treatment increased by1.36%～9.65%in the fourth quarter.（3）The influences of straw returning to the field and distinct fertilization methods on the water stability of soil aggregates with different particle sizes are different.In the rice season and the rape season,large aggregates with a diameter of>2 mm are dominant,accounting for 37.41%～46.10%and 36.44%～54.37%,respectively.Compared with F treatment,SF1 and NPK treatment remarkably raised the content of particle size aggregates with>2 mm and<0.25 mm in rice season,with increased of 7.49%～18.71%and14.26%～30.83%,while in rape season,the content of particle size aggregates with 1～2 mm,0.25～1 mm and<0.25 mm was mainly increased,with increased of 7.99%～13.72%,3.75%～21.96%and 7.17%～16.59%,respectively.（4）Straw returning to the field and different fertilization methods have different effects on the carbon and nitrogen components of aggregates with different particle sizes,and there was no significant difference in the contribution rate of DOC and DTN content in different particle sizes among different treatments.Straw returning significantly increased the contribution rate of soil organic carbon and components in large aggregates.Compared with F treatment,the SOC content of aggregates with SF1 and NPK treatment>2mm increased by 2.32%～12.64%;The largest contribution of POC content was from large aggregates>2mm,with an increase of 27.98%～34.27%（P<0.05）.Compared with F treatment,SF1 and NPK remarkably raised the content of TN in aggregates>2mm and0.25～1mm,with increases of 5.98%～25.38%and 24.34%～40.16%;The main contribution of PTN content was 1～2mm and 0.25～1mm aggregates,with the PTN content of 1～2mm and 0.25～1mm aggregates increasing by 6.61%～20.86%and 32.91%～65.41%（P<0.05）,respectively.（5）Compared to conventional fertilization,straw returning to the field and different fertilization methods increased rape,rice,and annual yield,with SF1 treatment having the highest yield,and SF2 treatment being able to reduce weight and stabilize yield.Moreover,with the increase in the number of years of straw returning to the field,the annual crop yield also significantly increases.Compared to 2021,the annual yield of rape,rice,and rice in 2022 increased by 1.36%～23.22%,0.95%～7.73%,and 0.29%～5.56%,respectively.The correlation between crop yield and soil aggregate carbon and nitrogen components showed that POC and PTN were significantly positively correlated with crop yield,while SOC and TN were significantly correlated with crop yield,indicating that relevant indicators were important indicators for improving crop yield.