Ammonia volatilization characteristics and emission coefficients of wheat and maize rotation in sandy fluvo-aquic soil under reduced N fertilization

Objective Nitrogen fertilizer application amount influences the total ammonia emission and nitrogen use efficiency directly. We studied the characteristics of ammonia emission under reduced nitrogen fertilizer input for the precise evaluation of the ecosystem effect.

Methods Sandy loam fluvo-aquic soils are typical farmlands in North China, a localized fertilization experiment was conducted in this type of soil, with winter wheat-summer maize rotation. Five N fertilizer treatments were setup in the experiment, namely no fertilizer control (CK), conventional (N), optimized (OPT), reduced optimized rate (LOPT) and combing chemical N with manure in optimized total N rate (mOPT). The N rates in treatments of N, OPT and LOPT were 315, 225 and 135 kg/hm² for wheat and 330, 240 and 150 kg/hm² for maize. The closed sponge method was used to monitor the ammonia emission amount during the growing season. The ammonia emission coefficient was calculated, the yield and N uptake of wheat and maize were analyzed.

Results The ammonia emission of maize season was 12.8–20.4 kg/hm², and that of wheat season was 6.8–12.0 kg/hm², accounting for 5.9%–8.5% and 3.3%–5.0% of the total N input in the two seasons. The overall ammonia emission in the maize season was significantly higher than that in the wheat season. Among the four N rate treatments, the ammonia emission coefficients of N and LOPT treatments were higher, those in wheat season were 3.8% and 5.0%, respectively, and in maize season were 6.2% and 8.5%; while the ammonia emission coefficients of OPT and mOPT treatments were relatively low, those in wheat season were 3.6% and 3.3%, and in maize season were 5.9% and 5.9%, respectively.The yields of wheat and maize in OPT and mOPTwere all significantly higher than those in N and LOPT treatments (P<0.05), which demonstrated that excessive or insufficient nitrogen application was not conducive to the production of crop yields in sandy loam fluvo-aquic soil. Appropriate manure application could not only increase production, but also reduce ammonia emissions. Fitting analysis showed that the ammonia volatilization of N treatments in the fluvo-aquic soil had a significant exponential increase after fertilization (P<0.01).

Conclusions The ammonia emission during maize season in the fluvo-aquic soil is generally higher than that during wheat season. The ammonia emission in maize season is higher after top dressing than after basal fertilization, and the emission in wheat season is higher after basal fertilization than after top dressing. Compared with conventional N application rate, optimized N rate could significantly decrease the ammonia emission amount and the emission coefficient of N fertilizer, no matter combined with organic fertilizer or not; while excessive reduced N rate would not decrease the emission coefficient of nitrogen fertilizers, in spite of the decreased emission amount. Comprehensively considering the yield and ammonia emission, optimized fertilizer is beneficial for both the yield and ecosystem effect under the tested area.