Inhibition of methane emissions from Chinese rice fields by nitrogen deposition based on the DNDC model

Nitrogen (N) deposition has rapidly increased in China, and its impact on ecosystems has received extensive attention. In the present study, the net effect of increased N deposition on methane (CH4) emissions from rice fields across China was evaluated using the validated DNDC (DeNitrification-DeComposition) model. The results showed that N deposition produces a slight increase in rice biomass and weakly inhibits CH4 emissions, under the current N fertilizer application practices (excessive N fertilizer) in paddy fields. Nationally, N deposition reduces total CH4 emissions by 0.04 Tg yr(-1). CH4 emissions are reduced by 1.38 and 1.69 kg CH4 ha(-1) yr(-1) (accounting for 0.6% and 0.2% of the average CH4 emissions) in a mid-season drainage water regime for single-and double-cropping rice, respectively. N deposition showed significantly influence on CH4 emission reduction (R = 0.86 and 0.74 for single- and double-cropping rice, respectively, p < 0.01). The largest reduction in the CH4 flux of single-cropping rice was mainly concentrated in AEZ (agroecological zone) 6A and AEZ 7, while the largest reduction for double-cropping rice was mainly distributed in the Poyang Lake Basin and Dongting Lake Basin. It should be noticed that the net response of CH4 emissions to N deposition ( - 0.07 and - 0.14 kg CH4 ha(-1 )kg(-1) N for single- and double-cropping rice, respectively) was greater than that to N fertilizers (- 0.05 kg CH4 ha(-1) kg(-1) N) under the same water management practices, which mainly because the nitrate nitrogen in N deposition increases the soil redox potential, thus inhibiting the production of CH4. These results provide a new understanding of the ecological effect of N deposition on agricultural ecosystems.