Effects Of Biochar And Straw Return On N₂O Emissions And Mechanism In Farmland Of The North China Plain

N2O is an important greenhouse gas, and the increasing of it’s concentration is an important cause of global warming. Thus reducing it’s emission has become an urgent way to solve the problem. Agricultural soil is an important source of N2O emissions. Based on the location experiment in North China, the effects and mechanisms of applying biochar and straw return on N2O emissions in wheat-maize rotation were studied. The experiment consisted of four treatments (CK, Cl, C2, SR) with three replications:CK (single NPK fertilizer), Cl (biochar 4.5;’t·hmr-2+NPK fertilizer) and C2 (biochar 9.0 t·hm-2+NPK fertilizer) and SR (straw return+NPK fertilizer). By the combination of field sampling and laboratory analysis methods, the effects of biochar and straw return on soil mineral nitrogen, pH, ammonia oxidizing bacteria, denitrifying bacteria, and the influences and effects of N2O emission in farmland of the North China Plain in 2014 and 2015 were studied. So as to provided a theoretical basis of mitigation of N2O emissions in North China’s farmland. The main results are as follows:(1) In the wheat-maize rotation cycle, the mineral N in the soil was dominated by NO3-N, and NH4+-N was kept at a low level. The content of soil mineral N in the whole growth period of winter wheat was higher than in that of summer maize. Application of biochar and straw return significantly increased soil NO3-N content. Compared with the treatment of straw return, the application of higher biochar was more helpful to the increase of soil NO3-N content. Application of higher biochar significantly increased soil pH.(2) In the wheat-maize rotation cycle, application of biochar and straw return were more helpful to increase soil the copy number of AOA, AOB, nirK, nirS, nosZ community. Soil ammonia oxidizing archaea is higher than ammonia oxidizing bacteria in the same crop. Application of biochar and straw return significantly increased nirK, nirS, nosZ copy number, nirK/nirS, (nirK+nirS)/nosZ ratio. The copy number of nosZ and nirK of soil in the wheat season were lower than that in the maize season.(3) In the wheat-maize rotation cycle, the dynamic changes of N2O flux was basically the same in each treatment. Application of low biochar significantly increased N2O emissions, and application of higher biochar helped to reducing N2O emissions. Straw return significantly increased N2O emissions in the maize season, but it significantly reduced N2O emissions in the wheat season. Whether in the maize or wheat season, there was a correlation between N2O emissions and soil nitrate, ammonium nitrogen content, and soil moisture. But there was a significant negative correlation between N2O fluxes and soil pH. There was a significant negative correlation between N2O emissions and copy number AOB in the wheat season. There was a negative correlation between N2O emissions and nosZ in the maize season.