Uso da terra, fertilidade do solo e degradação de pastagens: um estudo de caso em dois municípios no Cerrado brasileiro

Abstract

Scope and objectives: the reconciliation of agribusiness with environmental preservation is an undeniable and growing demand among opinion makers, consumers and governments in Brazil and abroad. Within this reality, this thesis aims to study three fundamental aspects in the sustainable use of Brazilian Cerrado lands, of which 100 million hectares are currently under agricultural use: the drivers of land use change, including deforestation of original vegetation; the characterization of the fertility of their soils under pastures and crops, as the main limiting factor to their agronomic use, and the degradation of pastures, as they occupy vast tracts of land for extensive cattle raising. Material and methods: interviews with farmers and other actors involved in agribusiness, literature review and census data, soil sampling for chemical analysis and agronomic classification of its fertility and a survey of the proportion of plant cover by the grass planted to measure pasture degradation were carried out in two municipalities of the State of Goiás, as a case study. Results and conclusions: subsidized rural credit was the main factor that allowed for a drastic deforestation in the 1970s in the studied municipalities, firstly when 90% of the region's vegetation was replaced by pastures and, to a lesser extent, annual crops, and secondly, in recent years, the sugar cane introduction, which replaced 100,000 hectares of pasture and crops. There is a wide variability and imbalance in soil fertility, independent of agricultural activity, particularly for phosphorus (P) and potassium (K) soil concentration plus generalized deficiency of calcium (Ca) and magnesium (Mg). Finally, considering that as a criterion a soil cover of the grass planted at least of 70% for a pasture is classified as degraded, 56% of the pastures evaluated are degraded in the studied municipalities.