Fertilizantes de liberação controlada e seus “blends” com ureia tratada com inibidor de urease para o cafeeiro

Abstract

Fertilizer technologies have been developed to minimize nitrogen losses and increase the efficiency of N use in coffee crop. Therefore, this paper aims to evaluate the fertilization of coffee trees using nitrogen fertilizers, the conventional one and the ones with different technologies – stabilized, controlled-release and blends (physical mixture) of both – applied in different doses, and their direct implications on the soil N stock and on the coffee yield after two harvests, through the evaluation of several characteristics of the fertilizers, the soil and the coffee plants. The experiment was conducted on a farm in Carmo da Cachoeira, Minas Gerais, Brazil, between 11/09/2017 and 6/30/2019, with the Mundo Novo cultivar IAC-379/19 (Coffea arabica L.). A randomized block design was adopted, with three replicates, 10 plants per plot, eight of which were used for evaluation. This work was divided into two experiments. Conventional Urea, Urea + NBPT (stabilized fertilizer), Urea Emax 41% (controlled-release) and Urea Emax 43% (controlled-release) and two blends of stabilized and controlled-release fertilizers: Blend 1 (40% Urea NBPT + 60% Urea Emax 41%) and Blend 2 (40% Urea NBPT + 60% Urea Emax 43%) were analyzed in both experiments. In the first experiment, seven treatments were evaluated, the six fertilizers were applied in a dose of 300 kg N ha-1, and a witness without fertilization. In the second experiment, the six fertilizers were evaluated in four application rates: 0, 150, 300 and 450 kg N ha-1, in a 6x4 factorial, totaling 24 treatments. The fertilization in Conventional Urea and Urea + NBPT treatments was divided in three applications, while the others were applied in a single application. The characteristics evaluated in the first experiment were: N release curve from controlled-release fertilizers and blends, in the field and in the laboratory; ammonia volatilization; crop yield and N use efficiency indexes. In the second experiment, the NTOTAL and NMINERAL stocks, N-NO3- and N-NH4+ of the soil, crop yield and N efficiency indexes were evaluated. Conventional Urea is the fertilizer that promotes the highest nitrogen losses by volatilization. There is no relation between the greatest losses by volatilization and crop yield. Coffee yield increases linearly with the increase of the applied N dose. But, the dose reduction from 450 to 300 kg of N ha-1 does not affect the coffee yield, besides not reducing the soil N stock. Urea + NBPT provides the lowest crop yield compared to other fertilizers and has the lowest rates of nitrogen use efficiency. The levels and stocks of NTOTAL, NMINERAL, N-NH4+ and N-NO3- increase with the increase of the applied N dose, but the insufficient N supply causes their reduction. Controlled-release fertilizers - Urea Emax 41% and Urea Emax 43% - and their "blends" with urease inhibitor-treated urea make it possible to carry out nitrogen fertilization of the coffee trees in a single application, making N gradually available to the plants, without affecting crop yield and soil N stocks and reducing losses by volatilization when compared to Conventional Urea.