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 low-carbon emission reduction provides a new pathway for safe and high-quality production of modern rice. In this study, the late-maturing medium japonica rices 'Nanjing 9108' and 'Taixiangjing 1402' mainly popularized in Jiangsu Province were selected as materials. Novel resin-coated controlled-release urea and quick-release urea (ordinary urea) were used as N fertilizers. Under the optimal operational ratio of 70% basal-tillering N fertilizers to 30% panicle N fertilizers, five treatments with different ratios of controlled-release N fertilizers to quick-release urea (here in after referred to as "controlled-to-quick ratios") with side-deep application of basal-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 (basal and tillering N fertilizers as quick-release urea broadcasted, FFT) and no N fertilizer application (0N) treatments were set up. 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 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. The D5∶5 treatment was significantly lower than the other treatments, with reductions of 58.31% and 61.59% for 'Nanjing 9108' and 46.72% and 49.42% for 'Taixiangjing 1402' compared to the FFT treatment. The next lowest was the D4∶6 treatment. (2) The 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 D5∶5 treatment had the lowest emissions, with reductions of 40.03% and 34.93% for 'Nanjing 9108' and 'Taixiangjing 1402' respectively compared to the FFT treatment, and both were significantly lower than the other treatments. However, the cumulative CH₄ emissions, greenhouse gas warming potential, and emission intensity significantly increased as the proportion of controlled-release N fertilizer decreased. The D10∶0 treatment had the lowest values, with reductions of 38.93%, 37.74%, and 39.53% for 'Nanjing 9108' and 41.32%, 40.04%, and 41.72% for 'Taixiangjing 1402' compared to the FFT treatment, and both were significantly lower than the other treatments. The next lowest was the D8∶2 treatment. 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.