Carbon sequestration potenciality of sugarcane harvesting without burning. / Potencialidade do sistema de colheita sem queima da cana-de-açúcar para o sequëstro de carbono.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

The present work was led in experimental areas installed by COPERSUCAR, in clay soil - Hapludox (Usina São Martinho) and sandy soil - Quartzipsamment (Usina da Pedra) in the area of Ribeirão Preto (SP). The objective was to analyze the influence of the deposited trash on the soil surface in relation to the dynamics of carbon in the sugarcane agrosystem since now alternatives are urged to decrease the emission of atmospheric carbon. The effect of the accumulation of trash was studied along the time (3, 4 and 5 years) and deposition of different amounts due to the accumulation of carbon in the system, as well as the granulometric distribution of it. The intra-annual behavior of trash was accompanied through measures along one year in experimental areas. The chemical and biochemical composition of the remaining trash was analyzed along the time and the influence of the crop without burning, due to the the imput of the greenhouse gas emission. That studies were developed along the years of 1998, 1999 and 2000. During the studied period, we found an average productivity of sugarcane by burning (88-101 Mg ha -1 ano -1 ) was 5% larger than without burning (85-95 Mg ha -1 ano -1 ) for the Hapludox and the Quartzpisament respectively. The trash deposited in an order of 13,9 Mg ha -1 ano -1 for the areas on Hapludox and 12,8 Mg ha -1 ano -1 for the Quartzpisament. After four years without burning a formation of a new humus horizon it was observed (trash), constituted of vegetable residues with different decomposition levels. In this horizon we distinguished, visually, three different layers: a new layer, more recent; an older layer, between one year and two years after the deposition and the oldest layer, with at least three years. The vegetable fabrics of two oldest layers were altered particularly by fungus with decrease of cellulose, a small lignin increase and a decrease of the C/N ratio. The fractionation of the trash demonstrated that most of it belonged to the fraction >4mm, with superior values of 50% in this fraction, and that the C/N ratio decreased with the decrease of the size of the fractions. The mass of accumulated dry matter in the trash after four years was 4,5 Mg ha -1 , and 1,1 Mg ha -1 for 1 year on Hapludox and 3,6 Mg have -1 (4 years), and 0,9 Mg ha -1 (1 year) on Quartzpisament. The soil factors and cane variety didn t influence the decomposition of the trash. But there was a positive effect for the amount deposited on the soil surface in relation to the accumulated amount along the years, for both soil types. A total of 1,5 Mg C ha -1 year -1 they were storage in the trash (0,5 Mg C ha -1 ano -1 ) and soil (1 Mg C ha -1 ano -1 ) compartment. The emissions of gases happened during burning of the trash before the cut of the sugar-cane they were calculated by data of literature. It was shown that the emission of N2O during the burning liberated an important amount of this greenhouse gas, expressed in C-CO2 (4,3 t C-CO2 have-1 year-1). The flows of gases on the soil surface were measured along one year with burning and without it burning on Hapludox. It was shown that the management without burning provoked a larger emission of CO2 and CH4 than the management with burning due to gas fixation. According to N2O, there was no difference on the emissions for the two management system. Due to the carbon stock compartments (plants, trash and soil) and the flows of the greenhouse gases, we established a balance of carbon in equivalent of emitted C-CO2 or sequestrated kidnapped by the management without burning, in comparison with the traditional burning system. The final result for Hapludox, in a period of 3 years, revealed a mitigation of 5 Mg C-CO2 ha -1 year -1 .

ASSUNTO(S)

cana-de-açúcar carbono palhada. colheita mecânica vegetable trash. mechanical harvest carbon sugarcane

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