Palhada de cana-de-açúcar em condição de cerrado : decomposição e disponibilidade de nutrientes

Abstract

Nowadays there are many discussions about the potential effects of sugarcane trash prevenient from the ending of farming burnings or post-harvest accumulation in the sugar cane growth. The sugarcane firing based harvest system without previous trash removal is a practice which promotes a new nutrient cycling dynamics, soil structuration, and also positive effects related to moisture conservation and water infiltration in the soil. This work aimed to study the sugarcane trash effect in a Acric Oxisol on the characteristics of dry matter production, its decomposition rate, the effect on the soil and the deployed macronutrients quantities. It was used decomposition bags with three doses of trash sugar cane, plus the treatment with dose zero. The material was placed perpendicular to the cane line and was collected in 7 time lapses inside one harvest period. A factorial scheme of 3X7 for the stubble doses and of 4X7 for the soil samples with four repetitions were used to study the effects of the fitomass decomposition and its implications in the soil. To analyze the behavior it was developed a specific exponential model for each trash doses capable of describing the degradation and elements liberation dynamics. It was verified a reduction of approximately 39% in the sugar cane trash mass for all the doses throughout a year. The initial C:N ratio of 174: 1 was reduced up to values near to 50%. The treatment of 18,5 Mg ha-1 of sugarcane trash has shown the greatest relative rate in carbon contribution originated from the sugar cane fitomass with 59% liberation of the initial value, which corresponds to 6,13 Mg ha-1 of C. There was a slight reduction in the sugar cane hemicellulose concentration, being this, the main responsible reducing the structural carbohydrates: hemicellulose, cellulose and lignin from 92% to 81%. Among the nutrients that contributed to the increase of their concentration in the soil, the treatment of 20 Mg ha-1 of sugarcane trash presented the greatest values for Ca and Mg with 34 and 9 kg ha-1 respectively. The greatest value of liberated potassium was identified in the treatment of 30 Mg ha-1 of sugarcane trash with 50 kg ha-1 of K. The deposition of this elements in the soil contributed to enhance its chemical characteristics in treatments of 20 and 30 Mg ha-1 of sugarcane trash with increasing concentration of Ca, Mg, K, organic matter, base sum, and base saturation percentage.