Legal restrictions from burning sugarcane prior to harvest are causing a sharp increase in acreage which is harvested as green cane. The presence of a thick sugarcane trash mulch left after harvest makes it difficult to incorporate fertilisers in the soil. Since large losses of ammonia may occur when urea is surface applied to trash, it is important to find ways to improve urea-N use efficiency. The urease inhibitor NBPT slows down urea hydrolysis and thus may help decrease ammonia losses. Ammonia traps were set up in seven sugarcane fields covered with trash and fertilised with ammonium sulfate or ammonium nitrate, urea, and NBPT-treated urea. All N fertilisers were surface-applied at rates of 80 or 100 kg N ha -1 . Very little N was lost when ammonium nitrate or ammonium sulfate were used. However, volatilisation losses as ammonia from the urea treatments varied from 1% (rainy days after fertilisation) to 25% of the applied N. The percentage of reduction in volatilisation due to NBPT application ranged from 15% to 78% depending on the weather conditions during the days following application of N. Addition of NBPT to urea helped to control ammonia losses, but the inhibitor was less effective when rain sufficient to incorporate urea into the soil occurred only 10 to 15 days or latter after fertiliser application. RESUMO: Restrições legais à colheita de cana-de-açúcar com despalha a fogo estão causando um aumento da área cultivada com cana crua. Essa prática gera uma espessa camada de palha de cana sobre o solo após a colheita, o que dificulta a incorporação de fertilizantes. Uma vez que grandes quantidades de amônia podem ser perdidas quando a uréia é aplicada superficialmente sobre a palha, é importante buscar alternativas para maximizar a eficiência de uso do N-uréia. O inibidor de urease NBPT retarda a hidrólise da uréia e pode contribuir para diminuir as perdas de amônia por volatilização. Para quantificar essas perdas, foram instaladas câmaras coletoras de amônia em sete áreas de produção de cana-de-açúcar colhida sem queima; estas foram fertilizadas com sulfato ou nitrato de amônio, uréia ou uréia tratada com NBPT. Todos os fertilizantes nitrogenados foram aplicados superficialmente em doses de 80 ou 100 kg ha -1 de N. As perdas de N foram muito pequenas quando se usou nitrato ou sulfato de amônio. Entretanto, as perdas por volatilização de amônia decorrentes do uso de uréia variaram de 1% (com dias chuvosos após a adubação) a 25% do N aplicado. O uso de NBPT proporcionou reduções de 15 a 78% nas perdas por volatilização, dependendo das condições climáticas nos dias posteriores à aplicação de N. A adição de NBPT à uréia ajudou a controlar as perdas de amônia, mas o inibidor foi menos efetivo quando chuvas suficientes para incorporar a uréia no solo ocorreram somente 10 a 15 dias, ou mais, após a aplicação dos fertilizantes. Palavras-chave: NBPT, adubos nitrogenados, perdas de amônia Cantarella et al.

There is a lack of information about fertilization of pineapple grown in the State of São Paulo, Brazil. So a field experiment with pineapple 'Smooth Cayenne' was carried out to study the effects of NPK rates on yield and fruit quality. The trial was located on an Alfisol in the central part of the State of São Paulo (Agudos county). The experimental design was an incomplete NPK factorial, with 32 treatments set up in two blocks. The P was applied only at planting, at the rates of 0; 80; 160 and 320 kg/ha of P2 0(5), as superphosphate. The N and K2O rates were 0; 175; 350, and 700 kg/ha, applied as urea and potassium chloride, respectively, divided in four applications during the growth period. Response functions were adjusted to yield or to fruit characteristics in order to estimate the nutrient rates required to reach maximum values. The results showed quadratic effects of N and K on yield and a maximum of 72 t/ha of fresh fruit was attained with rates of 498 and 394 kg/ha, respectively of N and K2O. In order to reach the maximum fruit size, and to improve the percentage of first class fruit (mass greater than 2.6 kg), were necessary rates of N and K respectively 11 and 43 % higher than those for maximum yield. No effect of P rates was observed on pineapple plant growth, despite the low availability of this nutrient in the soil. The effect of N rates was negative on total soluble solids and total acidity while the opposite occurred with K, which increased also the content of vitamin C. High yield and fruit size were closely related to N and K concentrations in the leaves.

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