DECOMPOSITION AND RELEASE OF NUTRIENTS FROM SUGARCANE TRASH IN TWO AGRICULTURAL ENVIRONMENTS IN BRAZIL

The decomposition and release of nutrients from unburned and mechanically harvested sugar-cane trash was evaluated under two agricultural environments in São Paulo State, Brazil. In the first agricultural environment (AE 1), part of a rain fed commercial field was used in the Ribeirão Preto region. In the second agricultural environment (AE 2), the study was conducted on an irrigated experimental area of the Escola Superior de Agricultura ‘Luiz de Queiroz’ in Piracicaba county. At this site, the influence of application of urea, potassium chloride and vinasse upon the decomposition of sugarcane trash was evaluated in lysimeters. Trash mass reductions of about 20% and 70% were observed at AE 1 and AE 2, respectively, after one year. Nutrient treatments did not affect trash decomposition or nutrient cycling at AE 2. The highest carbon losses, in both agricultural environments, came from decarboxilation of cellular contents and hemicellulose. Potassium was the most labile nutrient in crop residues, with 85–93% of the total potassium being released across sites in the study period. Only 20% of the total nitrogen was released. The release of calcium and magnesium ranged from 40% to 60%, across sites. In AE 1, there was no release of phosphorus and only 11% of the sulfur was released. However, in AE 2 the release of these nutrients reached 60%. The higher nutrient release and sugarcane trash decomposition in AE 2, comparative to AE 1, was due to greater decomposition of cellular contents and this may have been associated with protection of labile organics at AE 1 by higher lignin content and a consistent moisture regime provided by irrigation at AE 2.