Fertilização do campo nativo: efeitos na diversidade, produtividade e estabilidade

Abstract

The native grasslands are the food base of livestock and the main forage resource, with great economic, environmental and social importance for the "Pastizales del Río de la Plata" region in Brazil, Uruguay, Eastern Argentina and Southern Paraguay. These grasslands have great productive limitations related to the climatic seasonality and the low content of phosphorus and available nitrogen in the soils. Fertilization of native grasslands pasture is a viable alternative to improve primary and secondary livestock production. In this study the effects of nitrogen-phosphate fertilization of native field were analyzed using a six-year database of an experiment with continuous grazing of calves located in the northern region of Uruguay. The treatments consist of: I) Native Grasslands and II) Native Grasslands fertilized with Nitrogen (N) and Phosphorus (P2O5) in plots of two hectares with two replications. At the productive level there is a lack of indicators that help in decision making to optimize the productive and environmental management of this resource. Specifically, the study identified, from one hand, the fertilization long term effects on species richness, the C3/C4 ratio of dominant grasses, the productive response of grazing animals and, on the other hand, determined the temporal stability of both primary and secondary production. The N-P fertilization increased the calves’ daily gain, the stocking rate, the animal productivity in winter and spring, and the temporal stability of animal production. However, the N-P fertilization decreased the species richness by 40% and the stability of pasture production in spring, and also reduced calves’ daily gain and the stability of animal production in summer. In synthesis, the fertilization of grasslands with N and P fertilization causes positive and negative changes in the long term. These changes generate a dilemma when recommending this technologic tool. In this sense, new research is needed to develop indicators of sustainability, that will contribute to a decision support system for grasslands fertilization. The natural pasture indicators identified in the project will contribute to the construction of a support system for management decisions.