Effects of urea and ammonium sulfate on N_2O release pathway in an alkaline paddy soil

XING Zhi-qiang;XI Rui-ze;YANG Yong-qiang;ZHU Jun;HU Hong-qing;FU Qing-ling;College of Resources & Environment,Huazhong Agricultural University;Soil and Fertilizer Workstation of Linfen;

alkaline paddy soil;;N2O;;autotrophic nitrification;;denitrification;;heterotrophic nitrification

【Objective】The effects of soil water content and nitrogen fertilizer type on alkaline paddy soil N_2O release and release route were clarified,which provided a scientific basis for improving nitrogen use efficiency and reducing soil N_2O release.【Method】In this experiment,fluvo-aquic soil was used as the tested soil,soil moisture contents were adjusted through indoor culture,which was adjusting the maximum water holding capacity(WHC)to be 50%,80%,100%,120%and 160%,applying two types of nitrogen fertilizers: urea and ammonium sulfate(N 100 mg/kg). Acetylene(C_2H_2,10 Pa)and oxygen(O_2,100 kPa)were used to inhibit the autotrophic nitrification process and denitrification process of different nitrogen fertilizer types during 100% WHC. N_2O release,nitrate nitrogenand ammonium nitrogen contents were determined by gas chromatography and flow analyzer.【Result】The results showed that compared with no fertilization treatment(CK),urea and ammonium sulfate treatments significantly increased soil N_2O emission rate and cumulative emissions,and the effects of urea was greater than that of ammonium sulfate,and N_2O emission rate increased first and then decreased with the increase of water content. The N_2O emission rate of soil autotrophic nitrification and heterotrophic nitrification increased after nitrogen application,and the contribution of autotrophic nitrification to N_2O emission was greater than that of heterotrophic nitrification. However,the effects of urea and ammonium sulfate on the contribution of autotrophic nitrification and heterotrophic nitrification to N_2O emissions were different. The application of ammonium sulfate increased the contribution of autotrophic nitrification to N_2O emissions from 31.0%(CK)to 49.0% and reduced the contribution of heterotrophic nitrification from 63.0% to 5.3%;while urea reduced both the contribution of autotrophic nitrification and heterotrophic nitrification to N_2O emissions,from 31.0% to 25.0% and 63.0% to 1.7%,respectively.【Conclusion】With the increase of soil water content,the release rate of alkaline paddy soil N_2O increases first and then decreases. The cumulative release amount of urea N_2O under different water contents is higher than that of ammonium sulfate. The addition of nitrogen fertilizer reduces the contribution of heterogeneous nitrification to N_2O release. Ammonium sulfate and urea are dominated by autotrophic nitrification and denitrification,respectively. Therefore,the application of urea in dry soil and the use of ammonium nitrogen fertilizer in paddy field are beneficial to reduce N_2O release.