Effect of water addition and the urease inhibitor NBPT on the abatement of ammonia emission from surface applied urea

Urea is considered the cheapest and most commonly used form of inorganic N fertiliser worldwide. However, it has been estimated that 5–30% of the urea N is lost as volatilised NH3. Implementation of NH3 mitigation strategies is crucial in order to reduce both the economic and environmental impact associated with NH3 losses from urea application. Urease activity inhibitors and water addition to the soil have been proposed by UNECE (i.e. Gothenburg Protocol) as means to reduce NH3 emission from fertiliser applications. In this study, two field experiments were carried out in order to test the effectiveness of water addition as NH3 mitigation technique from surface applied urea in comparison with the use of the urease inhibitor NBPT. A system of wind tunnels was used to measure NH3 fluxes. Contrasting irrigation strategies (or rainfall patterns), in terms of both rate and timing, were used in order to evaluate the amount of water necessary to achieve a significant NH3 mitigation. The addition of 7 and 14 mm of water to the soil, immediately after urea spreading, reduced NH3 emission by 77 and 89%, respectively, similar to that achieved using NBPT (77–88% reduction). In contrast, a simulated 3 mm rainfall, immediately after fertilising, significantly enhanced NH3 volatilisation (with an 8% increase in emission compared to urea application without water addition). These results demonstrate the potential of correct water management in abating NH3 volatilisation from urea applications to soil, giving a similar effect to that of the urease inhibitor NBPT under the experimental conditions presented here.

Research highlights
► Effectiveness of water addition and the urease inhibitor NBPT, as NH3 mitigation techniques, was evaluated.
► A single watering was as effective as NBPT when mitigating NH3 from urea fertilising.
► Watering produced contrasting effects on NH3 emission depending on its rate and dose.
► These results add information to the sparse database on NH3 fluxes from urea fertilising.
► Although site-specific, these results provide supporting evidence for some UNECE NH3 mitigation strategies.