Effect Of Straw Return With Fertilizer Application On Nitrogen,Phosphorus And Runoff COD Loss From Farmland Under Rice And Wheat Crop Rotation Pattern

Fertilizer application and straw return are important for the rational use of resources.To investigate the effects of annual straw return under different fertilizer application patterns on crop yield,soil nutrient content and p H,and nitrogen,phosphorus and COD losses in field runoff,a straw return experiment was conducted in a rice-wheat rotation system with six treatments:treatment 1 no straw return+no fertilizer application（CK）;treatment 2 straw mulch return+no fertilizer application（S）;treatment 3 conventional（F）;treatment 4 straw clad return+conventional fertilizer（SDF）;treatment 5 straw mulch return+conventional fertilizer at 15%reduction（SFR）;treatment 6 straw mulch return+conventional fertilizer（SMF）.To provide an effective reference for the correct implementation of straw mulching and prevention of agricultural surface source pollution,the main findings are as follows:（1）During the rice-wheat crop rotation,the straw cladding treatment and the straw mulching treatment both reduced the mass concentrations of TN,NH₄⁺-N and NO₃^--N,but increased the mass concentrations of TP and COD in runoff under the same fertilizer application conditions;the reduction in fertilizer application effectively reduced the mass concentrations of N,P and COD in runoff under the same straw application conditions.The average mass concentrations of TN were reduced by10.96%to 18.33%and 2.37%to 14.39%for SDF and SMF respectively compared to treatment F.The average mass concentrations of TP and COD were increased by6.33%to 13.36%and 2.31%to 16.74%for SDF treatment compared to treatment F respectively.（2）Under the same fertilizer application conditions,both the straw cladding return treatment and the straw mulching return treatment could prevent and control the loss of N nutrients with surface runoff,but increase the risk of phosphorus nutrient and COD loss,while the straw mulch return treatment could effectively control the rate of phosphorus nutrient and COD loss;under the same straw return conditions,the reduction of fertilizer application could effectively reduce the risk of N,phosphorus and COD loss.Compared with the F treatment,TN loss from SDF and SMF was reduced by 15.55%to 28.18%（P<0.05）and 4.41%to 21.14%in the wheat and rice seasons,respectively.TP loss in the SDF and SMF treatments increased by 0.28%to5.53%in the wheat season compared to the F treatment;TP loss in the SDF and SMF treatments decreased by 0.55%to 0.56%in the rice season compared to the F treatment.COD losses were 2.41%higher in wheat season SDF compared to F treatment;COD losses were 3.21%lower in rice season SDF compared to F treatment.（3）Under the same fertilizer application conditions,both the straw cladding treatment and the straw mulching treatment significantly increased soil nutrient content and reduced soil p H.compared to F,the organic matter content increased by10.84%to 16.27%and 7.73%to 10.39%in the SDF and SMF treatments,respectively（P<0.05）;total nitrogen content increased by 6.38%to 9.31%and Total N content increased by 6.38%～9.31%and 4.57%～6.77%respectively（P<0.05）;total phosphorus content increased by 14.76%～21.11%and 12.19%～20.72%respectively（P<0.05）;soil p H decreased by 0.21%～1.40%in the SDF treatment compared to the F treatment.（4）Under the same fertilizer application conditions,both straw cladding and straw mulching treatments increased wheat-rice crop yields,and straw mulching with chemical fertilizer significantly increased wheat and rice yields compared to conventional local fertilizer application,while straw mulching with reduced fertilizer guaranteed crop yields.Wheat yields were significantly higher by 21.92%and14.01%（P<0.05）and rice yields were significantly higher by 28.09%and 22.82%（P<0.05）in the SDF and SMF treatments,respectively,compared to the F treatment.In summary,straw cladding with fertilizer treatment is a better way to prevent and control the loss of nitrogen,phosphorus and runoff COD from agricultural fields.Straw mulching with reduced fertilizer application can effectively control the loss of nitrogen,phosphorus and runoff COD from farmland while maintaining crop yield.