Water management at fertilization controls urease inhibitor performance in mitigating ammonia volatilization from temperate rice agrosystems

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Introduction Ammonia (NH 3 ) volatilization is one of the main pathways of nitrogen loss in rice paddies, reducing fertilizer efficiency and contributing to environmental pollution. Urease inhibitors such as NBPT (N-(n-butyl) thiophosphoric triamide) are commonly used to mitigate NH 3 emissions from urea-based fertilizers, but their effectiveness can vary depending on environmental conditions, particularly water management and temperature. Methods This study evaluated the effect of water management at fertilization (WMF) on NH 3 emissions from temperate rice agro-ecosystems (NW Italy). A field trial was conducted in 2024 where urea and urea + NBPT were applied and compared to ammonium sulfate under drained vs flooded conditions, with NH 3 emissions monitored over the 2 weeks following application. Soil N forms were monitored and agronomic parameters determined. Results Results show that NBPT effectiveness is strongly influenced by water management. Under drained conditions, the inhibitor reduced NH 3 emissions by approximately 72% compared with untreated urea, indicating inhibitor activation under aerobic conditions. Conversely, under flooded conditions, NBPT produced no significant reduction. When fertilization was conducted at higher mean air temperatures, the cooling effect of floodwater reduced NH 3 emissions more effectively than the inhibitor itself, highlighting the dominant role of temperature regulation. Ammonium sulfate showed negligible NH 3 losses across all conditions. Discussion Overall, the results demonstrate that the mitigation potential of NBPT in rice systems is governed by the balance between soil aeration and thermal conditions created by water management. NH 3 loss mitigation requires careful synchronization of fertilizer application, irrigation practices, and temperature conditions to maximize inhibitor performance and improve nitrogen use efficiency in rice production.