The Response Of Yield,Nutrient Uptake And Loss Of Double-Season Rice To Organic Fertilizer Substitution Ratio In Dongting Lake Region

The planting area of rice in Dongting Lake area is large,and the application of large amounts of chemical nitrogen（N）fertilizers has resulted in serious losses of N in rice fields.In recent years,the national agricultural department has attached great importance to the research and promotion of chemical fertilizer reduction and efficiency enhancement technologies.As the key technology,organic fertilizers instead of chemical fertilizers has been widely promoted by the Ministry of Agriculture.Appropriate application of organic fertilizer can significantly reduce the loss of nitrogen in paddy fields,but a large amount of application will result in insufficient nutrient supply and affect rice yield.Therefore,on the premise of stabilizing rice yield,determine the suitable replacement ratio of organic fertilizer for double-season rice cultivation in the Dongting Lake area is beneficial to minimize N loss and reduce the agricultural non-point source pollution risk in the region.Also,it is conducive to improve soil fertility,stable yield and increase N fertilizer utilization efficiency.To this end,in this study,under the same total N input in the rice field,7treatments were set（ie,no N,CK;conventional fertilization,ON0;organic fertilizer N instead of chemical fertilizer N 10%,ON0.1;organic fertilizer N instead of chemical fertilizer N 20%,ON0.2;organic fertilizer N instead of chemical fertilizer N 30%,ON0.3;organic fertilizer N instead of chemical fertilizer N 50%,ON0.5;organic fertilizer N instead of chemical fertilizer N 80%,ON0.8）,different research Effects of N substitution ratio of organic manure on the yield of double-season rice in the Dongting Lake area,nitrogen fertilizer utilization rate,ammonia field（NH3）volatilization loss,risk of nitrogen loss in field water,soil total nitrogen and organic carbon content.The main conclusions are as follows:1.Effect of organic fertilizer substitution ratio on double-season rice yield and N fertilizer utilization efficiencyAppropriate application of organic fertilizer can increase rice yield,while excessive application reduces it.Compared with conventional fertilization,the annual yield of double-season rice treated with ON0.1,ON0.2,ON0.3,and ON0.5 increased by 4.96%,6.91%,6.2%,and 3.93%,respectively,but with no significant difference.The highest yield treatment was ON0.2 with 16330 kg·hm^-2,followed by ON0.3,which was 16222 kg·hm^-2.The yield of ON0.8 was only 14628 kg·hm^-2,which was 4.23%lower than that of ON0,and significantly lower than ON0.1-ON0.5.With the application of organic fertilizer,the utilization rate of N fertilizer increased first,and then decreased with the increase of the N substitution ratio of organic fertilizer.The absorption and utilization rate of N fertilizer averaged 22.0%～41.9%,and the ON0.2 and ON0.3 were the highest treatments.Combining rice yield and N fertilizer utilization rate,ON0.2 and ON0.3 are more suitable organic fertilizer application methods under the experimental conditions.2.Effect of organic fertilizer substitution ratio on ammonia volatilization in double-season rice fieldsThe peak of NH₃ volatilization of early and late rice appeared 2-5d and 1-3d after fertilization,respectively.The total NH₃ volatilization loss（N loss ratio）of ON0 treatment in the double-season rice growing season was the highest,at 76.18 kg N·hm^-2（22.38%）.The total amount of NH₃ volatilization（N loss ratio）in the growing season of double-cropping rice treated with organic fertilizer was 42.26～68.13 kg N·hm^-2（12.81%～20.65%）,which decreased with the increase of the N substitution ratio of organic fertilizer.Compared with ON0,the application of organic fertilizer can significantly reduce the NH₃ loss of double-season rice,and the ON0.3,ON0.5,and ON0.8 treatments reduced by 34.85%,38.05%,and 44.52%,respectively.3.The effect of organic fertilizer substitution ratio on the risk of nitrogen loss from surface water in double-season rice fieldsThe TN and NH₄⁺-N contents of the surface water reached the peak during 1-3 days after fertilization,which was the key period to control the nitrogen loss of the surface water.Compared with conventional fertilization treatment,the application of organic fertilizer can significantly reduce the TN and NH₄⁺-N content of the field water,and the nitrogen in the field water mainly exists in the form of NH₄⁺-N.The average TN content of early and late rice treated with ON0 treated surface water was 9.56 kg·hm^-2 and 5.86 kg·hm^-2,respectively,and the average content of NH₄⁺-N was 9.04 kg·hm^-2 and 4.53kg·hm^-2,The average NH₄⁺-N accounts for 77.30%-94.56%of TN.With the increase of organic fertilizer proportion,the average content of TN and NH₄⁺-N in field water gradually decreased.Compared with ON0treatment,the average content of TN and NH₄⁺-N in the surface water of double-season paddy fields decreased by 2.93%～42.85%and 0.76%～58.55%.4.The effect of substitution ratio of organic fertilizer on soil total nitrogen and organic carbon in double cropping riceAfter two seasons of organic fertilizer application,the content of TN（total nitrogen）and organic carbon in the 0-20cm soil of the late rice season showed an increasing trend with the increase of the substitution ratio of organic fertilizer N,while the soil C/N was decrease,which indicated that the effect of applying organic fertilizer on improving soil organic carbon was better than soil total nitrogen.5.Relationship between related factors and total ammonia volatilization lossConsidering that NH₃ volatilization is an important way of nitrogen loss in paddy fields,we discussed the relationship between related factors and total ammonia volatilization loss.Correlation analysis showed that ammonia volatilization loss in the early rice season had a very significant negative correlation with the organic fertilizer N substitution ratio（r=-0.927**）,and a significant positive correlation with the average concentration of TN and NH₄⁺-N in the surface water（r=0.908*,r=0.909*）.The total NH₃ volatilization loss in the late rice season was significantly negatively correlated with the substitution rate of organic fertilizer N（r=-0.881*）,and was positively correlated with the average concentration of TN and NH₄⁺-N in field water（r=0.922**,r=0.868*）.The total ammonia volatilization loss in the two seasons was significantly negatively correlated with the ratio of organic fertilizer N（r=-0.919**）,soil TN content（r=-0.946**）,and the soil organic carbon content（r=-0.876*）significantly negative correlation.In conclusion,ON0.2 and ON0.3 treatments can achieve higher double-season rice yield,while reduce the risk of NH₃ volatilization,TN and NH₄⁺-N loss of field water,and increase soil total nitrogen and organic matter content.