Atividade da urease nas folhas do capim-marandu após aplicação de fontes nitrogenadas

Abstract

Despite the extractive practice in the cultivation of pastures in Brazil, Brachiaria cultivars, and in particular the marandu cultivar, have been taking up a lot of space in the country, due to their good development characteristics, good rooting, tolerance in soils with low fertility, resistance to dry spells, and also pasture leafhoppers, becoming the ideal forage in the cerrado. The objective was to evaluate the urease enzyme in the diagnostic leaf of marandu grass after application of nitrogen (N) sources, using the method adapted from Hogan, Seift and Done (1983) and McCullough (1967). The experiment was conducted within the campus of the Federal University of Mato Grosso/Araguaia in Barra do Garças-MT. The design was in randomized blocks with the source’s urea, ammonium nitrate (N.A.), NA + sulfur (S), NA + calcium (Ca), NA + S + Ca, NA + Ca + magnesium (Mg), Urea + NBPT, plus a control treatment, and four replications. Each plot had an area of 30 m2. The applied dose was 120 kg ha-1 of N divided into two applications. Six diagnostic leaves (LR) were collected per plot. Five collections were performed in total, with an interval of about 20 days between collections. A mass of 0.2 g was removed from these leaves, cut and placed in a water bath with phosphate buffer solution and urea pH (7.4) for 3 hours at 30 0C. Subsequently, an aliquot of each treatment and a blank without plant material together with reagent I composed of (phenol and sodium nitroprussianate) and reagent II composed of (disodium phosphate and sodium hypochlorite and sodium hydroxide), were again taken to the bath for 35 min at 37 0C, finally taken for absorbance reading in the spectrophotometer at 625 nm. The data were subjected to analysis of variance, and when they showed significant differences by the F test, the Skott knott test was performed using the SISVAR 4.6 statistical program. The activity of the enzyme urease in the diagnostic leaves of Capim-Marandu differed between N sources, regardless of the evaluated period.