Manejo da biomassa e sustentabilidade nutricional em povoamentos de Eucalyptus spp. em pequenas propriedades rurais

摘要

This study was conducted to achieve practical subsidies for nutritional management in Eucalyptus spp. stands in small farms located in Rio Grande do Sul state, Brazil. Di?erent stand ages were evaluated (2, 4, 6 and 8 years old), twenty-four (24) trees were sampled and biomass and nutrients were determined for the following components: leaf, live branch, dead branch, wood and bark from the trunk and root. Biomass and nutrient content in the understory and litter were also estimated. Biomass and nutrients stock in eucalypts were estimated through the product of the mean values for each component, diametric class and number of trees per hectare, and in understory and litter, it was obtained through extrapolation based on the sample unit areas. Utilization efciency from eucalyptus nutrients was estimated through the coefcient of biological utilization (CUB). Considering total nutrients stock in the eucalyptus, nutrients partition followed this order: Ca (40.0%), N (25.6%), K (22.6%), Mg (5.9%), S (3.1%), P (2.8%); and for component: trunk bark (27.5%), leaf (25.1%), wood trunk (22.5%), live branch (14.4%), root (9.4%) and dead branch (1.1%). Litter and understory play an important role in nutrients maintenance in forest ecosystems and accumulate (in average), based on the total stock for eucalyptus, for N, P, K, Ca, Mg and S, respectively, 47.1%, 34.0%, 33.6%, 32.8%, 35.3% and 36.6%. Forest harvesting in young stands leads to loss in wood yield and a higher nutrients relative export (lower CUB). The total eucalyptus biomass harvest above the soil, when compared to the harvest of only the trunk wood, increased the exports of N, P, K, Ca, Mg and S, respectively, in 83%, 152%, 193%, respectively. 445%, 305% and 49%, while the removal of biomass increased only 20%.