Mitigating ammonia volatilization in rice cultivation: The impact of partial organic fertilizer substitution

Optimizing water and nitrogen management to minimize NH₃ volatilization from paddy fields has been extensively studied. However, there is limited research on the combined effect of different rates of organic fertilizer substitution (OFS) and irrigation methods in rice cultivation, exploring an effective water and nitrogen combination is beneficial to mitigate NH₃ volatilization. To address this gap, we conducted a two-year field experiment to investigate NH₃ volatilization under different OFS rates (0%, 25%, and 50%) combined with continuous flooding irrigation (CF) and alternate wet and dry irrigation (AWD). Our findings revealed that NH₃ fluxes exhibited similar emission patterns after each fertilization event and significantly decreased with increasing rates of OFS during the basal stage. Compared to no substitution (ON0), the low (ON25) and high (ON50) rates of OFS reduced cumulative NH₃ emissions by 18.9% and 16.6%, and lowed NH₃ emission factors (EFs) by 26.7% and 23.3%, respectively. Although OFS resulted in a slight reduction in rice yield, yield-scaled NH₃ emissions were significantly reduced by 11.9% and 6.5% under the low and high substitution rates, respectively. This reduction was mainly attributed to the slight yield reduction observed at the low substitution rate. Furthermore, when combined with ON0, AWD irrigation had the potential to increase NH₃ volatilization. However, this increase was not observed when combined with ON25 and ON50. During each fertilization stage, floodwater ⁺ concentration emerged as the prominent environmental factor influencing NH₃ volatilization, showing a stronger and more positive correlation compared to other factors such as floodwater pH, soil pH, and NH₄⁺ concentration. Based on our findings, we recommend implementing effective water and nitrogen management strategies to minimize NH₃ volatilization in rice cultivation. This involves applying a lower rate of organic fertilizer substitution during the basal stage, maintaining high water levels during fertilization, and implementing mild AWD irrigation during non-fertilization periods.