Fertilizantes nitrogenados convencionais, estabilizados, de liberação lenta ou controlada na cultura do cafeeiro: eficiência e custos

Abstract

Nitrogen fertilization has a direct economic and environmental impact in the management of soil fertility in coffee plantations. The application of urea on the soil surface can result in substantial losses of nitrogen by volatilization, leaching and denitr ification, causing the low utilization and recovery of this nutrient. The purpose of this study was to evaluate the efficiency, influence and costs of conventional nitrogen fertilizers, stabilized, with a slow release and a controlled release in coffee pla ntations in Lavras – MG – Brazil. The experimental design used was with completely randomized blocks with three replicates. The treatments were divided into two groups: Group 1, of conventional and stabilized fertilizers: Conventional urea, Urea dissolved in water, Ammonium sulfate, Ammonium nitrate, Urea + Cu + B, Urea + anionic polymer and Urea + NBPT; Group 2 of the slow or controlled release fertilizers: Urea + S 0 + polymers, Urea + plastic resin, Urea formaldehyde and Urea + water insoluble polymer. N itrogen fertilizations were done differently among the treatment groups. For Group 1, the N supply was made in 3 fertilizations at intervals of approximately 60 days, from November to March, each at a dose of 100 kg N per hectare. For Group 2, only one fertilization was done, according to the manufacturers' recommendations, of 300 kg ha -1, together with the first fertilization of Group 1. The evaluated characteristics were: volatilization of ammonia, superficial pH of soil, leaf N, S and Cu contents, estimated productivity and production cost. The fertilizers that presented higher losses of nitrogen by ammonia volatilization were Urea + anionic polymer (24.89%) and conventional Urea (22.98%). Those ones with the lowest losses were: Urea formaldehyde (0.46%) , Ammonium sulphate (0.23%) and Ammonium nitrate (0.18%). The soil pH in the 0 to 5 cm layer decreases after fertilization. The final soil pH means of each fertilizer did not differ from each other. Urea + anionic polymer was the fertilizer that more acidified the soil throughout the experiment. There was no correlation between the highest losses with leaf nutrition by nitrogen. N and S leaf contents did not vary among fertilizers after the fertilizations. Cu leaf contents varied. Urea + S 0 + polymer provided higher productivity (48.27 bags ha-1). The fertilizer that presented the lowest total operating cost per hectare was Urea + Cu + B (R$ 11,018.68), while Urea + plastic resin obtained the highest one (R$ 16,358.05). The highest gross profit per hectare was obtained by the fertilizers Urea + S 0 + polymers (R$ 10.743,76) and Urea + NBPT (R$ 9,784,61).