The effects of nitrogen fertilizer deep placement on the ammonia volatilization from paddy fields in the Taihu Lake region of China

.Ammonia (NH₃) volatilization is an important nitrogen (N) loss pathway in paddy fields. However, the effects of N fertilizer deep placement, slow-release N fertilizers, and urea inhibitors on NH₃ volatilization reduction during the entire rice-growing season remain uncertain. To fill this knowledge gap, we conducted a field experiment with seven treatments: (1) no N application, (2) local broadcasting application of urea at a rate of 300 kg(N)∙hm⁻² (SN300), (3) 10% reduction of N from SN300 (SN270), (4) deep placement of basal urea together with the broadcasting of topdressing of urea at tiller and panicle stages of rice, at a total a rate of 270 kg(N)∙hm⁻² (DN270), (5) application of urea inhibitor for DN270 (DN270+UI), (6) 10% nitrogen reduction, deep application of basal urea together with the surface application of slow-release N fertilizer (DN270+SR), and (7) application of urease inhibitors for DN270+SR (DN270+SR+UI). Compared with the SN300 treatment, deep placement of basal N fertilizer reduced the cumulative NH₃ emissions by 78.2%−85.2% in the basal fertilization period. The combined application of the urease inhibitors in the rice topdressing periods (DN270+UI treatment) reduced the NH₃ emissions by 30.4% at the tillering stage and 25.3% at the panicle stage in comparison with the SN300 treatment. Replacing urea with a slow-release N fertilizer (DN270+SR treatment) in the rice topdressing periods reduced NH₃ volatilization by 36.4% at the tillering stage and 28.1% at the panicle stage. The cumulative NH₃ volatilization changed in the following order: SN300 > SN270 > DN270 > DN270+UI > DN270+SR > DN270+SR+UI. Compared to the local treatment (SN300), DN270+SR+UI significantly reduced NH₃ volatilization by 50.9%. There was no significant difference in rice yield among the N fertilizer treatments. NH₃ emission intensity per unit rice yield was lowest for the DN270+SR+UI treatment, 52.5% lower than the SN300 treatment. Overall, simultaneous N fertilizer deep placement with slow-release N and urease inhibitors produced more grains with lower environmental costs associated with NH₃ emissions. This represents a promising and sustainable management strategy for paddy fields in the Taihu Lake region of China.