Produtividade de um campo natural de Planossolo do bioma Pampa fertilizado com sulfato de amônio

Abstract

It is evident, nowadays, that the only way to preserve natural pastures is making them express all their productive potential and, thus, be used in an economically viable way. This way, it was evaluated for three years the productivity and quality of a natural grassland of Planosol subjected to increasing levels of nitrogen in spring and summer (0, 40, 80, 120, 160, 200, 240, 280 kg/ha of N) and autumn (0, 20, 40, 60, 80, 100, 120, 140 kg/ha of N), in the form of ammonium sulfate. The experiment was conducted at the Palma Agricultural Center of Federal University of Pelotas, located in Capão do Leão County (RS). Three cuts (spring, summer and autumn) were performed to evaluate dry forage mass, accumulation rate, dry matter and crude protein. After being evaluated for their normality by the Kolmogorov-Smirnov test, the data were analyzed using ANOVA, Tukey mean comparison test and polynomial regression (P≥0.05). Water availability is essential for optimizing the response of the natural grassland, requiring higher levels of nitrogen fertilization in years of water deficit. In years with adequate water availability, fertilizations up to 220,8 and 216,5 kg/ha of N were sufficient to reach maximum productivity in spring and summer, respectively. In autumn, the maximum values were obtained with the application up to 82,0 kg/ha of N. The maximum forage quality, in terms of crude protein, was not reached even under levels up to 280 kg/ha of N, with values averages up to 116,3 g/kg.