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Nitrogen (N) is an important nutrient for melon (Cucumis melo L.) production. However there is scanty information about the amount necessary to maintain an appropriate balance between growth and yield. Melon vegetative organs must develop sufficiently to intercept light and accumulate water and nutrients but it is also important to obtain a large reproductive-vegetative dry weight ratio to maximize the fruit yield. We evaluated the influence of different N amounts on the growth, production of dry matter and fruit yield of a melon 'Piel de sapo' type. A three-year field experiment was carried out from May to September. Melons were subjected to an irrigation depth of 100% crop evapotranspiration and to 11 N fertilization rates, ranging 11 to 393 kg ha -1 in the three years. The dry matter production of leaves and stems increased as the N amount increased. The dry matter of the whole plant was affected similarly, while the fruit dry matter decreased as the N amount was increased above 112, 93 and 95 kg ha -1 of N are sufficient for adequate plant growth, development and maximum production. To obtain fruit yield close to the maximum, the leaf N concentration at the end of the crop cycle should be higher than 19.5 g kg -1 . Key words: LAI, LAD, dry matter accumulation, production functions, leaf nitrogen concentration Dinâmica do crescimento e da produtividade do melão em resposta ao fertilizante nitrogenado RESUMO: O nitrogênio (N) é um nutriente importante para a produção de melão (Cucumis melo L.), porém existe pouca informação sobre a quantidade necessária para se obter um balanço entre o crescimento e a produtividade. Os órgãos vegetativos do melão precisam se desenvolver suficientemente para interceptor luz, acumular água e nutrients, mas também é importante alcançar uma grande relação de massa seca produtiva-vegetativa para maximizar a produção de frutos. Investigou-se a influência de quantidades de N no crescimento, na produção de matéria seca e na produtividade do melão tipo 'Pele de sapo'. Foi conduzido experimento com três anos de duração, de maio a setembro, com irrigações de 100% da evapotranspiração e 11 doses de adubação de N, no intervalo de 11 a 393 kg ha -1 em três anos. A produção de massa seca de folhas e caules aumentou com o aumento das doses de N. A matéria seca da planta toda foi afetada de maneira semelhante, enquanto a dos frutos decresceu com o aumento de N acima de 112, 93 e 95 kg ha A dose mais baixa de N reduziu a produtividade de frutos em 21%, enquanto a dose mais alta aumentou o crescimento vegetative, LAI e a duração de área foliar (LAD), mas reduziu a produtividade em 24% em relação ao tratamento N 93 . Aplicações excessivas de N aumentam o crescimento vegetativo às expensas do crescimento vegetativo. Para este tipo de melão, doses da ordem de 90-100 kg ha -1 de N são suficientes para crescimento adequado e produção máxima. Para obter produções próximas ao máximo, a concentração de N na folha no final do ciclo da cultura não deve ser maior que 19.5 g kg -1 . Palavras chave...

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Th e present study reviews the most common N effi ciency indexes with a view to maximizing yield and minimizing N loss, for melon grown in a zone where the water supply has a high nitrate content due to environmental degradation. Th e N use effi ciency (NUE) values of the study were those relating the fruit yield (FY) and the dry weight (DW) with N applied (N ap ), N available (N av ), and N uptake (N up ), which were denominated NUE 1 , NUE 2 , NUtE, NUE 3 , NUE 4 , and NUE 5 , respectively. A 3-yr fi eld experiment (2005, 2006, and 2007) was performed from May to September in central Spain. Melon crops were irrigated at 100% of the ET c (crop evapotranspiration) and 11 N rates, ranging from 11 to 393 kg ha -1 (considering N fertilizer [N f ], applied over 10 wk, and N in the irrigation water [N w ], where the NO 3 concentration was 5.58, 80.64, and 10.89 mg L -1 in 2005, 2006, and 2007, respectively), were applied to a soil classifi ed as Alfi sol Xeralf Petrocalcic Palexeralfs. Th e results show a clear relationship between crop N up and both FY and DW. Of the potential yield, 95% could be obtained with a N application of 93 kg ha -1 . Th e maximum FY was observed with a N up of 155 kg ha -1 . Th e NUE, when related to N ap and N av , showed an exponential trend and when related to N up a linear trend, delimiting a range within which the optimum value of N occurs.

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The need to reduce nitrogen (N) fertilizer pollution strengthens the importance of improving the utilization efficiency of applied N to crops. This requires knowledge of crop N uptake characteristics and how fertilization management affects it. A three-year field experiment was conducted from May to September in central Spain to investigate the influence of different N rates, which ranged from 11 to 393 kg ha -1 , applied through drip irrigation, on the dynamics of N uptake, nitrogen use efficiency (NUE), fruit yield and quality of a 'Piel de sapo' melon crop (Cucumis melo L. cv. Sancho). Both N concentration and N content increased in different plant parts with the N rate. Leaves had the highest N concentration, which declined by 40-50% from 34-41 days after transplanting (DAT), while the highest N uptake rate was observed from 30-35 to 70-80 DAT, coinciding with fruit development. In each year, NUE declined with increasing N rate. With N fertilizer applications close to the optimum N rate of 90-100 kg ha -1 , the fruits removed approximately 60 kg N ha -1 , and the amount of N in the crop residue was about 80 kg N ha -1 ; this serves to replenish the organic nutrient pool in the soil and may be used by subsequent crops following mineralization.Additional key words: Cucumis melo; fertilization; N distribution; N use efficiency; N removal; N in crop residues. ResumenInfluencia de la fertilización nitrogenada en la dinámica de absorción de nitrógeno, producción y calidad del melón 'Piel de sapo'La necesidad de reducir la contaminación procedente de la aplicación de fertilizantes nitrogenados refuerza la importancia de mejorar la eficiencia de utilización del nitrógeno aplicado a los cultivos. Durante tres años se realizaron ensayos de campo al aire libre en los meses de mayo a septiembre en la zona centro de España para investigar la influencia de distintas dosis de N, en la dinámica de absorción de N, eficiencia del uso del N (NUE), producción y calidad de un cultivo de melón (Cucumis melo L. cv. Sancho) 'Piel de sapo'. Las dosis de N variaron desde 11 a 393 kg ha -1 y se aplicaron a través del riego por goteo. Tanto la concentración como el contenido de N aumentaron en las distintas partes de la planta a medida que la dosis de N aumentó. La hoja fue el órgano con la mayor concentración de N, decreciendo un 40-50% a partir de los 34-41 días después del transplante (DAT). La tasa de absorción de N más alta se observó desde los 30-35 hasta los 70-80 DAT, coincidiendo con el desarrollo del fruto. En cada año, el NUE descendió con el incremento de la dosis de N. Con aplicaciones de N cercanas a la dosis óptima de 90-100 kg ha -1 , los frutos extrajeron aproximadamente 60 kg N ha -1 , y la cantidad de N en el residuo del cultivo estuvo alrededor de 80 kg N ha -1 . Este residuo sirve para rellenar la reserva de nutrientes orgánicos del suelo y puede ser usado por los cultivos posteriores después de su mineralización.Palabras clave adicionales: Cucumis