| Summary: | Substantial ammonia (NH<sub>3</sub>) losses from rice production result in poor nitrogen (N) use efficiency and environmental damage. A data synthesis using the published literature (127 studies with 700 paired observations), combined with an incubation experiment using 50 paddy soils from across China, were conducted to improve the current understanding of the NH<sub>3</sub> loss from paddy rice and its drivers. The efficacy of the urease inhibitor Limus<sup>®</sup> for reducing NH<sub>3</sub> losses was also evaluated. The mean loss of N, through NH<sub>3</sub> volatilization, was 16.2% of the urea-N applied to paddy rice. The largest losses were from double rice cropping systems, and losses increased with the N application rate, surface application of N, unstable N types (ammonium bicarbonate and urea), and high floodwater pH. Under simulated flooded conditions, urea amended with Limus<sup>®</sup> reduced NH<sub>3</sub> loss by 36.6%, compared to urea alone, but floodwater pH had a significant effect on inhibitor efficacy. Key driving factors were air temperature, N application rate, and floodwater pH. The effectiveness and limitations of the inhibitor in NH<sub>3</sub> emission mitigation was examined, as well as its basis as one means of N pollution control in paddy rice cropping systems.
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