Efeitos do momento de adubação após a desfolha de cultivares de Brachiaria brizantha

Abstract

The fertilization of pasture aims to help maintain pasture productivity through the replacement of nutrients, but little is known about the dynamics of fertilization moments after defoliation. Thus, the objective was to verify the adequate moment for nitrogen and potassium fertilization after defoliation, to identify the effect of reserve compounds in the roots and to evaluate the effects on different Brachiaria brizantha cultivars. The experiment was conducted in a greenhouse at the Federal University of Mato Grosso and at the Federal University of Rondonópolis, in an entirely randomized design with 5 repetitions. The treatments consisted of fertilization days after defoliation (0; 3; 6 and 9 days), and three experiments were studied with the cultivars Marandu, Piatã and Xaraés. Productive, morphogenic, structural and chlorophyll index characteristics, nitrogen and carbohydrate contents and accumulation in the root system were evaluated. For Marandu grass, there was a linear decreasing effect of days after defoliation only for total root nitrogen content. For Piatã, there was an effect of days after defoliation on the following variables: stem+hair dry mass, tiller, total nitrogen, soluble carbohydrates and starch. For Xaraés, there was an effect of days after defoliation on the following variables: leaf blade dry mass, stem+hair dry mass, forage mass, leaf mass, number of leaves, tiller, as well as total nitrogen, starch and total nonstructural carbohydrates. Among the grasses, Xaraés showed the lowest starch fraction and the highest forage mass. The highest carbohydrate accumulation was in Marandu, but there was no effect on nitrogen accumulation. The moment of fertilization after defoliation does not alter the development of Marandu and Piatã cultivars. The cultivar Xaraés is influenced by the fertilization interval, reaching maximum forage production when fertilized on the fifth day after defoliation. The accumulation of soluble carbohydrates, starch and total nonstructural carbohydrates does not directly affect the forage mass production of the grasses.