Emissões de gases de efeito estufa e estoque de carbono e nitrogênio em área de plantio misto de eucalipto e acácia no norte mato-grossense

Abstract

Eucalyptus is the most cultivated forest species in Brazil, having economic and environmental importance. However, in order to exploit its maximum productive potential, is necessary the correct replacement of nutrients through fertilization, through the application of chemical fertilizers, specially nitrogen (N), that is the main source of nitrous oxide (N2O). The adoption of mixed eucalyptus plantations with nitrogen-fixing legumes trees appears as a sustainable alternative to supply nitrogen to eucalyptus, without the application of nitrogen fertilizers, to reduce N2O emissions, without compromising productivity. The objectives of the study were to evaluate the greenhouse gas emissions, nutrient stock in the litter and to evaluate the organic C and N stocks in the soil in the mixed plantation with eucalyptus and acacia. For these, a study was carried out in the experimental area of Embrapa Agrossilvipastoril, in Sinop-MT. Five treatments were evaluated: eucalyptus monoculture, with nitrogen fertilization (E+N); monoculture eucalyptus (E); monoculture of acacia (A); mixed planting with 67% eucalyptus and 33% acacia (67E:33A) and; 50% eucalyptus and 50% acacia (50E:50A). The experimental design was a randomized complete block design, with three replications. GHG samplings were carried out in the dry season (19 months after planting) and rainy period (23 and 24 months after planting), using static chambers base-top model and analyzed by gas chromatography. The height evaluations were performed with Vertex hypsometer and the circumference at chest height (CBH) was measured with a tape measure, at 1.30 cm from the soil and later transformed into diameter at breast height (DBH). These evaluations were carried out at 15 and 26 months after planting, and the litter collections, with a template (0.25 m2 ) and soil, for carbon and nitrogen analysis, were performed at 29 months. For the N2O in the dry period the treatments did not present significant differences in the emission of N2O. In the rainy season, the E+N treatment presented higher emissions, which may have occurred due to the higher availability of N in the soil, increasing the activities of denitrifying microorganisms. Nitrogen fertilization did not alter tree growth, litter nutrient stock, soil C and N. Mixed plantations can be beneficial to long-term treatments when there is no competition between species. GHG emissions are lower in mixed planting. Up to 29 months, the litter stock, C and N of the soil are the same for all treatments.