Influence of burning and weed control on the soil fertility and vegetation cover of Brazilian Amazon pastures

Abstract

In pastures it is common to use fire to control weeds, justified by the increase in soil fertility that ashes can generate. However, the benefits of this process is short-lived, and also increase the soil exposure. The permanence of weeds can contribute to the vegetation cover in areas of deficient pastures. This study aimed to evaluate the effect of prescribed burning and mowing on vegetation cover of Urochloa brizantha (U. brizantha) pastures and soil surface fertility in pastures located in the Brazilian Amazon. The study was conducted in Itupiranga, Pará state, Brazilian Amazon. Five pastures of U. brizantha cv. Marandu and a forest area were evaluated. The soil was a Ferralsol. Vegetation cover was estimated using a quadrat. Four composite soil samples were taken in each area, collected from 0–0.05 m depth. The percentage of vegetal cover of U. brizantha, weeds and bare soil was measured and fertility in soil samples (pH, Al3+, Ca2+, Mg2+, K+, Na+, P, and H+Al) were determined. Three groups were identified in the evaluated pasture plots. Group I had the highest average percentage of bare soil (33.5%) and was associated with H+Al and P values. Group II had the highest average of U. brizantha cover (90%) and was associated with Ca2++Mg2+ and K+. Group III had the highest average of weed cover (53.4%) and was associated with Al3+. The higher percentage of U. brizantha in Group II was favored by the burning later. This group presented better levels of K+, Mg2+ and sum of bases. The management adopting the least use of fire on the pastures, with longer time for the regeneration of forage, combined with the mechanical control of weeds, can be the best alternative for maintaining the soil cover and bringing benefits for quality surface layer of the soil.