Num solo calcário (Entissolo) da parte central da região costeira do Peru, foram estudadas, em casa de vegetação, as perdas por volatilização do N-ureia (10,191% átomos 15N) e N-sulfato de amônio (7,801% átomos 15N), aplicados como adubo de cobertura na cultura de milho. Nos vasos com 1.500g de terra, o N foi aplicado na dose de 150 μg/g. Os adubos localizados de quatro maneiras (na superfície do solo seco, superfície do solo úmido, superfície do solo seco com irrigação imediata e enterrado a 4cm em solo úmido), foram aplicados quando as plantas de milho (quatro/vaso) tinham quinze dias após a emergência (DAE). As perdas do N-fertilizante, por volatilização, foram calculadas através do balanço de massa do N aplicado, no final do experimento (45 DAE). Encontrou-se que: a) a ureia (65%) superou o sulfato de amônio (52%) no aproveitamento pela cultura, sendo que o aproveitamento dos adubos foi maior quando foram aplicados na superfície do solo seco ou enterrados em solo úmido; b) a ureia deixou mais N residual no solo, mas não houve diferenças significativas nas formas de localização; c) a perda do N-sulfato de amônio (39%), por volatilização, superou sensivelmente a ureia (23,6%); d) as perdas do N-fertilizante aplicado na superfície do solo úmido (42%) ou seco com irrigação imediata (37%) superaram sensivelmente as aplicações na superfície de solo seco (23,4%) ou enterrado em solo úmido (22%).A study was performed in greenhouse to investigate the volatilization losses on nitrogen from 15N labelled urea (10.191 atom % 15N) and ammonium sulphate (7.801 atom % 15N) applied to pots of a calcareous soil (Entisol) from the central coastal region of Peru. The pots contained 1.5 kg of soil and were planted with four maize plants. The labelled N was added at a rate of 150 μg N.g-1 soil at 15 days after emergence (DAE) of the maize. The N fertilizer were applied in four different ways: on the surface of the dry soil, on the surface of the wetted soil, on the surface of the dry soil but immediately irrigated, or buried at a depth of 4cm in wetted soil. The losses of fertilizer N, by volatilization were calculated from a mass balance of the applied labelled N at the end of the experiment (45 DAE). It was found that: a) a greater proportion of the N from urea (65%) was taken up by the plant than that provided by ammonium sulphate (52%) and fertilizer use efficiency was greater when the fertilizers were applied to the surface of the dry soil or buried in wetted soil; b) the urea left more residual N in the soil but there were no significant differences between the addition methods; c) the loss of N from ammonium sulphate 39%), by volatilization, was greater than that from urea (23,6%); d) the losses of fertilizer N applied to the surface of the wetted soil (42%) or from that applied to dry soil which was immediately irrigated (37%) were significantly greater than when the fertilizer was applied to the surface of dry soil (23,4%) or buried in wet soil (22%)
