The use of inorganic nitrogen (N) fertilizers in grasslands is likely to increase as restrictions on manure applications are implemented. Concerns have been raised about the economic and environmental impact of N loss from these fertilizers through ammonia (NH3) volatilization. This study evaluated NH3 volatilization losses from urea, urea ammonium nitrate (UAN) and urea-polymer (UP) applied to grazed, tall fescue (Festuca arundinacea sp) pastures at 50 kg N ha -1 in fall and spring. Fertilizers were applied in triplicate circular plots (30-m diameter) and ammonia loss was measured by the modified passive flux method for 70 days following application. In fall 2004, urea lost significantly more (p<0.05) NH3 (16% of applied N) than UAN and UP (5%). In contrast, in spring 2005 there were no significant differences in NH3 volatilization among treatments (p<0.05), with an average loss of 8 % of the applied N. Lack of significant differences in spring 2005 may have been due to the occurrence of intense rainfall immediately after fertilizer application.
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