Effect of ratios of controlled-release nitrogen fertilizer to ordinary urea with side-deep application on NH₃ volatilization and greenhouse gas emissions in paddy field

The innovative demonstration of side-deep application technology combining slow/controlled-release nitrogen (N) fertilizer with urea for low ammonia volatilization and carbon emission reduction provides a new pathway for the safe and high-quality production of modern rice. In this study, the late-maturing medium japonica rices ‘Nanjing9108’ and ‘Taixiangjing1402’, mainly popularized in Jiangsu Province, were selected as materials. Novel resin-coated urea and quick-release urea (ordinary urea) were used as N fertilizers. Under the optimal operational ratio of 70% base and tillering N fertilizers to 30% panicle N fertilizers, five treatments with different ratios of controlled-release N fertilizer to quick-release N fertilizer (herein after referred to as “controlled-to-quick ratio”) with side-deep application of base and tillering fertilizers were established: 10∶0 (D10∶0), 8∶2 (D8∶2), 6∶4 (D6∶4), 5∶5 (D5∶5), and 4∶6 (D4∶6). Additionally, conventional fertilizer application (base and tillering N fertilizers such as quick-release N fertilizer broadcasted, FFT) and no N fertilizer application (0N) treatments were established. The NH₃ volatilization, N₂O and CH₄ emission patterns, and environmental impacts of different “controlled-to-quick ratio” treatments were analyzed. The results showed that: 1) For both rice varieties, the whole growth period cumulative NH₃ volatilization and emission intensity of different “controlled-to-quick ratio” treatments first decreased and then increased as the proportion of controlled-release N fertilizer decreased, and these indicators under the D5∶5 treatment were significantly lower than the other treatments, with reductions of 58.31% and 61.59% for ‘Nanjing9108’ and 46.72% and 49.24% for ‘Taixiangjing1402’ compared to the FFT treatment. The next lowest was the D4∶6 treatment. 2) The whole growth period cumulative N₂O emissions of both rice varieties also followed a trend of first decreasing and then increasing with the decreasing proportion of controlled-release N fertilizer. The whole growth period cumulative N₂O emissions under D5∶5 treatment had the lowest emissions, with reductions of 40.03% and 34.93% for ‘Nanjing9108’ and ‘Taixiangjing1402’, respectively, compared to the FFT treatment, and both were significantly lower than the other treatments. However, the whole growth period cumulative CH₄ emissions, global warming potential, and greenhouse gas emission intensity increased as the proportion of controlled-release N fertilizer decreased. The whole growth period cumulative CH₄ emissions of the two varieties under the D10∶0 treatment was the lowest. The global warming potential, and greenhouse gas emission intensity of ‘Nanjing9108’ under the D10∶0 treatment were also the lowest, while these two indicators of ‘Taixiangjing1402’ under the D8∶2 treatment were the lowest, which showed no significant difference compared to the D10∶0 treatment. Compared to the FFT treatment, the whole growth period cumulative CH₄ emissions, global warming potential, and greenhouse gas emission intensity under D10∶0 treatment decreased by 38.93%, 37.74%, and 39.53% for ‘Nanjing9108’ and 41.30%, 40.04%, and 41.72% for ‘Taixiangjing1402’. In summary, the “controlled-to-quick ratio” of 5∶5 is suitable for high-yield and ammonia-controlled production for japonica rice, while the “controlled-to-quick ratio” of 10∶0 favors green, low-carbon, and emission-reduction production.