The wheat crop in São Paulo State, Brazil, is fertilized with N, P and K. The rate of applied N (0 to 120 kg.ha -1 ) depends on the previous grown crop and the irrigation possibility. The response of wheat to rates and time of N application and the fate of N applied to irrigated wheat were studied during two years. Residual N recovery by soybean grown after the wheat was also studied. The maximum grain productivity was obtained with 92 kg.ha -1 of N. The efficiency of 15 N-urea utilization ranged from 52% to 85%. The main loss of applied 15 N, 5% to 12% occurred as ammonia volatilized from urea applied on soil surface. The N loss by leaching even at the N rate of 135 kg.ha -1 , was less than 1% of applied 15 N, due to the low amount of rainfall during the wheat grown season and a controlled amount of irrigated water, that were sufficient to moisten only the wheat root zone. The residual 15 N after wheat harvest represents around 40% of N applied as urea: 20% in soil, 3% in wheat root system and 16% in the wheat straw. Soybean recovered less than 2% of the 15 N applied to wheat at sowing or at tillering stage. No Estado de São Paulo, a cultura do trigo é adubada, além de P e K, com N, cuja dose (0 a 120 kg ha -1 ) depende do cultivo anterior e da possibilidade de irrigação. A resposta do trigo às doses e épocas de aplicação e o destino do N aplicado foi estudada em dois cultivos de trigo, seguidos pela soja. Também se avaliou a recuperação do N residual pela soja cultivada nas mesmas parcelas após o trigo. A produtividade máxima estimada de grãos seria obtida com a dose de 92 kg.ha -1 de N. A eficiência de absorção 15 N-uréia variou de 52% a 85%. A principal perda de N, que variou de 5% a 12%, ocorreu através de volatilização de amônia proveniente da uréia aplicada na superfície do solo. Por lixiviação foi perdido menos que 1% do N aplicado, pois a água da chuva ou da irrigação foi suficiente para molhar somente a camada do solo onde se encontrava o sistema radicular do trigo. O N residual após o cultivo do trigo correspondeu a 40% do total aplicado, posto que 20% permaneceu no solo, 3% na matéria vegetal radicular do trigo e 16% na matéria vegetal da palha do trigo, depositada sobre o solo. A soja recuperou menos que 2% do 15 N aplicado no solo na semeadura ou no perfilhamento do trigo.Palavras-chave: adubação nitrogenada, eficiência, amônia, volatilização.A.E. Boaretto et al.

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Urea with micronised sulfur (S) in granules may result in lower nitrogen (N) depletion through ammoniacal N (NH3-N) loss than conventional urea due to the acidification reaction of S near urea granules in soil, and the addition of S to the urea may provide a limiting nutrient in tropical soils. The research objectives were to (1) verify whether urea containing micronised S (urea+S) can mitigate NH3-N volatilisation in comparison to conventional urea, ammonium nitrate, and ammonium sulfate; and (2) evaluate the efficiency of N and S sources for common bean (Phaseolus vulgaris L.) grown on coarse-, medium-, and fine-textured soil. The results showed that ~90% of NH3-N volatilisation occurred during the first 14 days after application. The blend of elemental sulfur and sulfate in urea reduces the loss of N by NH3-N volatilisation compared with regular urea but not enough to achieve the low volatilisation as observed for ammonium nitrate and ammonium sulfate application. Despite the differences in the leaf N and S concentration and bean yield components, no differences were observed among N sources in grain yield in general.

The study evaluated the potential agricultural use of kamafugite as a multi-nutrient fertilizer in the cultivation of Urochloa brizantha. Two experiments were carried out under greenhouse conditions, one using a Ferralsol and the other an Arenosol. The experimental design was a randomized block with four replicates, in a factorial scheme 4 × 2 + 2, comprising four doses of kamafugite (1667, 3334, 6668, and 13336 mg dm-3), two product forms (filler and powder), and two additional treatments, TSF + KCl and a control treatment without K2O and P2O5 application. The sources were incubated for 60 days on two soil types and, after the incubation period, Urochloa brizantha plants were grown and two consecutive cuts were performed. The kamafugite was efficient in increasing plant dry mass and the levels of P, K, Ca, and Mg accumulated in plants, mainly in the 2nd Urochloa brizantha crop. The granulometry filler was more efficient in the sandy soil and the form powder in the clayey soil. Kamafugite can be used as an alternative source of nutrients for the Urochloa brizantha crop, being a low-cost and a potential source to improve tropical soil fertility over time.

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