The effects of deep application of nitrogen fertilization on ammonia volatilization in a winter wheat/summer maize rotation system in the North China Plain

The deep application of nitrogen fertilizers can reduce soil ammonia volatilization, but no annual systematic study in a winter wheat/summer maize rotation system exists. Nitrogen fertilizer was deeply applied to soil from a winter wheat/summer maize rotation system to determine the effects on ammonia emissions and optimize farmland fertilization. Five treatments were used from October 2018 to October 2019:no fertilization (CK), conventional fertilizer surface-application (T₁), slow-release fertilizer surface-application (T₂), twice layered deep-application of slow-release fertilizer (T₃), and single layered deep-application of slow-release fertilizer (T₄). Ammonia volatilization primarily occurred in the corn top-dressing season and accounted for 84.84% of the annual ammonia volatilization. The cumulative amounts of annual ammonia volatiles were 22.75 (T₁), 6.17 (T₂), 2.25 (T₃), and 0.55 kg·hm^-2(T₄), accounting for 4.86%, 1.32%, 0.48%, and 0.16% of the total fertilizer application, respectively. The slow-release fertilizer treatments reduced the ammonia volatilization loss by 72.88% (T₂), 90.11% (T₃), and 96.30% (T₄) compared to T₁. The single deep application treatment (T₄) avoided the summertime high soil ammonia volatilization period, and the cumulative annual ammonia emissions were comparable to the unfertilized emissions (0.43 kg·hm^-2). The annual yields were 8.31 (CK), 13.20 (T₁), 12.66 (T₂), 14.42 (T₃), 14.22 (T₄) t·hm^-2; and compared with T₁, the slow-release fertilizer deep application increased the crop yield by 9.25% (T₃) and 7.75% (T₄). The surface application of slow-release fertilizer (T₂) slightly decreased the yield but significantly reduced the ammonia volatilization amount. In conclusion, the deep application of slow-release nitrogen fertilizer improved crop yield and reduced soil ammonia emissions, and was shown to be a simple, efficient, and environment-friendly fertilization method.