Nitrate Leaching and Ammonia Volatilization Under Different Nitrogen Management Practices.

In a series of field studies, differing rainfall patterns within the first month after nitrogen (N) fertilizer application to a coarse-textured soil were found to significantly affect yield and N use efficiency of irrigated corn, and that response varied with N source. A laboratory study was conducted to explore in more detail interactions of N source with precipitation events following N application to a coarse-textured soil. Nitrogen sources included urea-ammonium nitrate solution (UAN), UAN with additives of either nitrapyrin (Instinct®) or a polymer (Nutrisphere-N®), or polymer-coated urea (PCU) (ESN®). These products were applied to soil in chambers from which ammonia (NH₃) volatilization and nitrate (NO₃^-) leaching were measured over a period of 31 days following fertilization. Precipitation events simulated rainfall frequency and amount which occurred in field studies in 2009 (dry conditions) and 2011 (wet conditions). Ammonia volatilization was lower in wet than in dry conditions. Total NH₃-N loss for the dry precipitation regime ranged from 11-18% of applied N fertilizer for all treatments except for the PCU (<1% of applied of N). In contrast, all treatments in wet conditions had NH₃-N loss extremely low (<1% of applied N). However, substantial NO₃-N leaching occurred with wet conditions, in the range of 48-65% of applied N for most treatments. Leaching loss was the greatest for UAN, followed by UAN with additives. Polymer-coated urea effectively protected against either NH₃ volatilization or NO₃-N leaching, depending on the precipitation regime. The UAN-IN and UAN-NS treatments generally reduced loss compared to UAN alone. However, these additives were less effective than PCU when heavy precipitation occurred very soon after fertilization.