ManageMent of IrrIgatIon and nItrogen fertIlIzers to reduce aMMonIa VolatIlIzatIon

nitrogen losses by ammonia (nH 3) volatilization can be reduced by appropriate irrigation management or by alternative n sources, replacing urea. the objective of this study was to evaluate the efficiency of irrigation management and N source combinations in decreasing NH 3 volatilization from an Argissolo Vermelho Distrofico tipico cultivated for 28 years with black oat (Avena strigosa) and maize ( Zea mays), under no-tillage in the region of depressao central, rio grande do sul, Brazil. the experiment was arranged in a randomized block design with split plots with three replications, where the main plots consisted of irrigation systems: no irrigation; irrigation immediately before and irrigation immediately after fertilization. the subplots were treated with different n sources: urea, urea with urease inhibitor and slow-release fertilizer, at an n rate of 180 kg ha -1 , broadcast over maize, plus a control treatment without n fertilization. ammonia volatilization was assessed using semi-open static collectors for 1, 2, 4, 6, and 10 days after n fertilization. In general, more than 90 % of total nH 3-n losses occurred until three days after n fertilization, with peaks up to 15.4 kg ha -1 d -1 . The irrigation was efficient to reduce NH 3 losses only when applied after n fertilization. However, reductions varied according to the n fertilizer, and were higher for urea (67 %) and slightly lower for urea with urease inhibitor (50 %) and slow-release fertilizer (40 %), compared with the mean of the treatments without irrigation and irrigation before fertilization. the use of urea with urease inhibitor instead of urea was only promising under volatilization-favorable conditions (no irrigation or irrigation before n fertilization). c ompared to urea, slow-release fertilizer did not reduce ammonia volatilization in any of the rainfed or irrigated treatments.