Total organic fertilizer substitution of nitrogen fertilizer in Erhai watershed can satisfy rice nitrogen nutrition and reduce gaseous reactivenitrogen emission in paddy fields

Objectives Erhai watershed is an important water resource and ecological threshold of Yunnan Province. The chemical nitrogen fertilizer has been prohibited and application of organic fertilizer are promoted for conservation of water quality. We studied the feasibility of complete substitution of chemical fertilizers with organic resources in rice production of th area.

Methods A rice field experiment was conducted for two years (two season) in Dali Autonomous Prefecture, Yunnan Province from 2021 to 2022. Chemical fertilizer N rate was used as control amount (CF), and green manure (GM), cow dung (CD), pig manure (PM), and chicken manure (CM) were applied in equal N amount. Ammonia volatilization in rice fields were monitored since the first day of fertilization using intermittent air sampling-acid-base titration in situ method, and the total N and dissolved organic N in the surface water were measured at the same time. N₂O emissions were monitored using the static dark box-meteorological chromatography in situ method. At harvest, rice yield and nitrogen accumulation were analyzed.

Results Based on two years of data, the four organic substitution treatments were recorded similar rice yield, aboveground N accumulation, and nitrogen fertilizer utilization efficiency with CF treatment. Compared with CF in 2021 and 2022, the organic fertilizer treatments reduced the NH₃ volatilization rate by 65.15%−85.61%, and 91.51%−96.25%, decreased cumulative NH₃ volatilization by 89.81%−96.04%, and 97.19%−98.72%, and reduced NH₃ volatilization loss by 89.81%−96.04%, and 97.15%−98.79%. The organic fertilizer substituting treatments reduced 56.21%−72.39% of total N₂O emissions than CF.

Conclusions Complete substitution of chemical fertilizer with local organic fertilizers can ensure the nitrogen nutrition rerquirement and yield of rice, reduce NH₃ volatilization and N₂O emissions significantly, indicating the feasibility of complete organic fertilizer substitution in both rice production efficiency and the reduction of gaseous active nitrogen emissions in Erhai watershed, Yunnan Province.