Biomassa e nutrientes do híbrido Eucalyptus urograndis e Acacia mearnsii em plantios monoespecíficos e mistos

Abstract

The stock of biomass and nutrients has been the basis of many studies in forestry, particularly those that assess the nutritional sustainability of the system, however, there are few studies on this basis in mixed plantings in the final rotation. Given this, the present study was to evaluate the biomass and nutrients for the hybrid Eucalyptus urograndis and Acacia mearnsii in monospecific and mixed plantings, at 9 years old. For this, we carried out the study in the experimental area in the city of Pinheiro Machado/RS, which consisted of 3 treatments with pure and mixed plantation of Eucalyptus urograndis (E) and Acacia mearnsii (A) (100% E, 100 % A, 50% E + 50% A), in a randomized blocks with four repetitions. For dendrometric evaluation, the DAP all individuals is gauged and height 20% of individuals, establishing a ratio of height according to the diameter to estimate the height of the remaining individuals. To estimate the stock of nutrients in the soil were opened three trenches in the center of each plot to block 1, 2 and 3. The above-ground biomass was determined by reference to the average tree in each plot based on DAP species in planting. CUB was calculated by the ratio of the biomass and the amount of each component of the nutrient and biomass estimate of nutrient removal by harvesting the biomass was made for three scenarios. The growth of Acacia mearnsii was higher in mixed stands as compared to monospecific, but the hybrid Eucalyptus urograndis showed lower growth in mixed planting. The stock of available soil N to 60 cm depth was higher in mixed stands as compared to monospecific planting hybrid Eucalyptus urograndis. Analogous to growth, the hybrid Eucalyptus urograndis stock showed lower biomass in the mixed stand compared to their monospecific planting, since the Acacia mearnsii presented accumulation of higher biomass in mixed planting. Acacia mearnsii showed higher amounts of nutrients in the mixed stand when compared to its monoculture and the reverse was observed for the hybrid Eucalyptus urograndis. Wood was the component that larger CUB values for all analyzed nutrients. Removing only the commercial stem wood it is characterized as the best biomass harvesting stage in order to reduce the impact of nutrition and nutritional activity sustainability of the site.