Losses by volatilization of 15 N-urea and 15N-ammonium sulphate from a calcareous soil of the central coastal region of Peru

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%)