Effects of different fertilization methods on ammonia volatilization from rice paddies

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Rice paddies are one of the most important anthropogenic sources of ammonia (NH3) emissions. The seasonal cumulative NH3–N loss accounts for 9%–60% of the total amount of applied nitrogen (N) fertilizer. Deep placement fertilization (DPF) can effectively improve N fertilizer use efficiency. However, unlike the conventional surface broadcasting fertilization method (CF), DPF technology can only be used to apply basal fertilizer (BF) in the rice paddies. It is currently unclear how CF and DPF fertilization methods influence NH3 volatilization at different BF application ratios. Therefore, an in situ field experiment was conducted in east China to investigate the effects of CF and DPF fertilization methods on NH3 volatilization from rice paddies under BF application ratios of 40%, 55%, 70%, 85%, and 100% (seasonal applied N fertilizer = 260 kg N·hm−2). Two background treatments: a control (no fertilizer) and N blank (applied with P and K fertilizers), were employed so that the NH3 volatilization-induced N losses could be calculated. The results indicated that the DPF treatments significantly reduced NH3 volatilization by 23.13%–60.57% under the different BF application ratios compared to the CF treatments. The mitigation effect of DPF on NH3 volatilization was only observed during the BF application period. Compared to the CF treatments, the DPF treatments markedly reduced the maximum BF application-induced NH3 volatilization fluxes by 39.78%–76.03% under the different BF application ratios. In contrast, no clear differences in top-dressing fertilizer-induced NH3 volatilization were observed between the CF and DPF treatments at the different BF application ratios. These results showed that DPF technology combined with a higher BF application ratio can effectively mitigate NH3–N losses from rice paddies.