Liberação de nitrogênio de ureia de disponibilidade gradual em função da temperatura e do tempo de incubação

Abstract

The environmental conditions affect the release of nitrogen (N) from slow release fertilizers. The objective of this work was to evaluate the effect of temperature and incubation time on N release of three slow release ureas. The percentageof total N of the tested ureas was 39 (Experiment 1; U39), 38 (Experiment 2; U38), and 37% (Experiment 3; U37). The experiments were carried out in laboratory at the University of Passo Fundo, Brazil, in 2014. The experimental units were tetra pak boxes containing 200 g of an Oxisol and the tested ureas (except the Control). These materials were incubated in chambers with temperature control. Thetested ureas were coated with elemental sulfur (S 0 ) and biodegradable polymers. The concentration of these substances were 11 and 1.5% (U39), 14 and 2.5% (U38), 16 and 3.0% (U37), respectively. Temperature and time of incubation were the evaluated factors. The experiment was a randomized block design (three replications). The tested temperatures were 5, 15, 25, 35 and 45 °C. The N release was evaluated for up to 90 (Experiment 1), 150 (Experiment 2), and 210 days(Experiment 3) of incubation. The effect of incubation time and the temperature on the percentage of N released from the granule and on the content of mineral and total soil N and pH were evaluated. TheN source (Slow release x conventional urea) effect on these variables was also evaluated. In all experiments, the lowest release of N was found at 5 (19 to 40%) and 15 °C (36 to 44%), depending on thetested urea. The 15 lowest temperatures also decreased total and mineral N increments on soil N and the pH value. At the end of the experiments, N released from the fertilizers was higher at 35 °C (71 and 90%, U37 and U38, respectively) or at 45 °C (96%, U39). Nitrogen release increases with time and temperature of incubation. This effect was higher at 90 (U39), 150 (U38) and 210 (U37) days and at25 to 45 °C.