Ammonia fluxes and emission factors under an intensively managed wetland rice ecosystem.

Nitrogen (N) loss from rice production systems in the form of ammonia (NH) can be a significant N loss pathway causing significant economic and environmental costs. Yet, data on NH fluxes in wetland rice ecosystems are still very scarce which limits the accuracy of national and global NH budgets. We measured the NH fluxes in situ in a wetland rice field and estimated emission factors (EF) under two soil management systems (i.e. conventional tillage, CT and strip tillage, ST); two residue retention levels (i.e. 15%, LR and 40% crop residue by height, HR); and three N fertilization rates (i.e. 108, 144 and 180 kg N ha) in two consecutive years (2019 and 2020). The highest NH peaks were observed within the first 3 days after urea application. The mean and cumulative NH fluxes significantly increased with the increases in N fertilization rates and were 18.5% and 18.6% higher in ST than in CT in 2020 but not in 2019. Overall, the highest mean NH fluxes were in 180 kg N ha coupled with either HR or LR and ST or CT. In 2019, the NH EF was unchanged by any treatments. In 2020, the lower EF was in CT coupled with LR (15%) than all other treatment combinations, where ST with HR showed the highest EF (20%). Likewise, the lowest N rate (108 kg N ha) in ST had the highest NH EF (20%) that was similar to higher N rates (144 and 180 kg N ha) in the same tillage treatment and to 180 kg N ha in CT. Our results highlight that NH fluxes in rice field particularly the effects of ST correlated with higher soil pH and NH content and lower redox potential. Our results highlight that NH fluxes are a potentially large N loss pathway in wetland rice under conventional and decreased soil disturbance regimes.