Abstract: 【Objective】Optimization of water and nitrogen management measures has a great significance for rice yield improvement and greenhouse gas emission reduction in paddy fields. To establish water and fertilization management regimes with effects on yield promotion and greenhouse gas mitigation, a new water-saving irrigation technique, “thin and shallow alternate wetting drying”, was investigated in the double rice cropping system. Synergistic effects of water-saving irrigation and new types of nitrogen fertilizer on rice yield and greenhouse gas emissions were evaluated. 【Method】The study focused on double rice cropping system in the Jianghan Plain, Hubei province, Central China. Greenhouse gas emissions were observed from four different treatments: U＋CI: urea with conventional traditional irrigation, as the control (CK); U＋SI: urea with “thin and shallow alternate wetting drying” water-saving irrigation; CRU＋SI: polymer-coated urea with “thin and shallow alternate wetting drying” water-saving irrigation; NU＋HQ＋SI: nitrapyrin crystal urea with hydroquinone and “thin and shallow alternate wetting drying” water-saving irrigation. Measurements were taken using the automatic static chamber-GC (gas chromatography) method. CH₄ and N₂O emissions, and total CO₂-eq (CH₄＋N₂O, on a 100a horizon) of each treatment were analyzed. Rice yield per plot and greenhouse gas intensity (GHGI) were calculated after harvesting. 【Result】The “thin and shallow alternate wetting drying” water-saving irrigation technique diminished CH₄ emission fluxes during the early and late rice seasons, especially at the reproductive stage, resulted in lower CH₄ emissions for U＋SI compared to U＋CI (P<0.01). The reduction in CH₄ emissions in the late rice season was greater than in the early rice season. By using water-saving irrigation techniques, pronounced differences in CH₄ emissions were identified among polymer-coated urea, nitrapyrin crystal urea with hydroquinone and urea treatments. Total CH₄ emissions during two rice seasons from CRU＋SI and NU＋HQ＋SI were 60% and 73% of emissions from the U＋SI treatment, respectively. “Thin and shallow alternate wetting drying” water-saving irrigation increased N₂O emissions in paddy fields. Compared to U＋CI, the U＋SI treatment significantly increased N₂O emissions in the early and late rice seasons by 34% and 39%, respectively (P<0.05). Compared to urea, N₂O emissions from nitrapyrin crystal urea with hydroquinone and polymer-coated urea treatments were decreased. The effect of nitrapyrin crystal urea with hydroquinone on the control of N₂O emissions was superior to that of the other two nitrogen fertilizers. A trade-off was identified between CH₄ and N₂O emissions under “thin and shallow alternate wetting drying” irrigation, but the effect on the reduction of CH₄ emissions was greater than the increase in N₂O emissions. Overall, “thin and shallow alternate wetting drying” irrigation can reduce total greenhouse gas emissions, with the strength of the mitigation effect depending on the type of nitrogen fertilizer used. Polymer-coated urea had the greatest mitigation effect, reducing total CO_2-eq emissions by 49%, followed by nitrapyrin crystal urea with hydroquinone (46%) and urea (28%). Furthermore, polymer-coated urea and nitrapyrin crystal urea with hydroquinone were more beneficial for rice yield promotion and decreased greenhouse gas intensity of rice production. 【Conclusion】The results suggest that “thin and shallow alternate wetting drying” water-saving irrigation has good effects on yield maintenance and GHG abatement. The combined application of water-saving irrigation and polymer-coated urea or nitrapyrin crystal urea with hydroquinone could further increase rice yield and reduce greenhouse gas emissions. Thus, these water and nitrogen management measures deserved wider extension in order to simultaneously increase grain yield and decrease global warming effects.

Key words: rice, water saving irrigation, controlled-release fertilizer, urease/nitrification inhibitor, greenhouse gas, yield