Effects Of Biochar Application On Yield,NH₃ Volatilization And N₂O Emission Of Rice-wheat Rotation System In Different Seasons

To understand the effects of biochar in ensuring rice and wheat yields and reducing nitrogen emission losses,elucidating the mechanism of BC influencing nitrogen utilization in rice-wheat rotation system during growing season,the typical rice-wheat rotation system was studied in this study.Three nitrogen application levels（N280,N350,N420）and treatments for biochar addition at different seasons（rice season:R,wheat season:W）were settled,determining the key indicators of rice and wheat yield,NUE,topsoil（0-20 cm）or surface water pH,NH₃ volatilization,N₂O emission and others,for providing theory and data support for the stable production of rice-wheat rotation system,nitrogen efficiency and emission reduction,and the application of BC.The main findings of the study are as follows:（1）During the rice season,the application of biochar treatment at the wheat season can increase the effective ears,grains of rice in the rice season at different nitrogen application levels and increase the yield of rice.During the wheat season,the application of biochar treatment at the wheat season can also increase the yield of 280 kg N ha^-1 year^-1 and 350 kg N ha^-1 year^-1 nitrogen levels by 6.49%and 3.88%respectively compared with the N280 and N350treatments,by increasing the wheat harvest index.Biochar applied at nitrogen level of 350 kg N ha-1 year-1（rice season and wheat season）performs better.The rice grain yield increased by8.71%.Biochar increased NUE of rice by 25.71%at 350 kg N ha-1 year-1 nitrogen application level and increased NUE of wheat at 350 kg N ha^-1 year^-1 and 420 kg N ha^-1 year^-1 nitrogen levels（10.36%-16.10%）.（2）Biochar reduced 9.86%NH₃ volatilization flux and 27.43%cumulative NH₃volatilization in the rice-wheat rotation system at nitrogen level 350 kg N ha^-1 year^-1.Biochar had different effects on the NH₃ volatilization of rice-wheat rotation system in different seasons and the effect of biochar applied at rice season on rice was more significant,reducing the NH₃volatilization of rice by 33.21%.The application of biochar at the wheat season had more significant effect on wheat,reducing the NH₃ volatilization of wheat by 41.92%.（3）Compared with the non-biochar treatments,the effect of biochar at rice season is more significant,which can reduce the N₂O emission of rice by 6.85%-14.52%.Biochar applied at the wheat season increased the N₂O emission of wheat by 17.57%-25.33%at the nitrogen application levels of 280 kg N ha^-1 year^-1 and 350 kg N ha^-1 year^-1.The application of biochar at wheat season increased N₂O emission of wheat by 35.96%-37.58%.The application of biochar at rice season had no significant effect on the overall N₂O emission of the rice-wheat rotation system.However,the applying biochar at wheat season will increase the overall N₂O emission of the rice-wheat rotation system compared with the treatment of no biochar application（26.15%-40.24%）.In summary,biochar reduced N₂O emission and NH₃ volatilization of 350 kg ha^-1 nitrogen treatment compared with no biochar treatment.Biochar increased yields of rice and wheat,and biochar applied at wheat season performed better.Therefore,based on appropriately reducing nitrogen inputs,the purpose of reducing nitrogen loss in rice-wheat rotation systems and ensuring crop yields can be achieved by applying biochar at the wheat season.