Implicações silviculturais da colheita da biomassa e da remoção de nutrientes de um povoamento de Eucalyptus saligna

Abstract

It is vitally important to know the nutritional sustainability of homogeneous stands of Eucalyptus spp., compared to the proper management of forest enterprises in forest harvesting, and understanding regarding the maintenance of soil fertility of these settlements. The objective of this study was to evaluate the impact of different harvest intensities about nutritional balance of a seven years old Eucalyptus saligna stand in Barra do Ribeiro, RS. For this, the quantification of tree biomass, accumulated litter on soil and understorey, quantification of nutrient stock in each of these compartments was performed. A simulation of different forest harvesting systems was carried out, the number of rotational potential was determined and the coefficient of biological utilization was determined for each tree biomass constituent in order to verify the nutritional sustainability of the stands. The total tree biomass eucalyptus was 222.11 Mg ha-1, with greater representation by the shaft housing (wood + bark), which contributes 90.5% of the biomass produced. The total nutrient stock in the allocated tree biomass was 1.43 Mg h-1, and the magazine shaft is presented to a larger contribution to the allocation of these nutrients. The components of the biomass had different compositions (P < 0.05), whereas the highest levels were found in the sheet and the smaller compartment the timber compartment. The accumulated litter on the ground presented a biomass of 17.48 Mg ha-1 and a nutritional contribution of 0.44 Mg ha-1. The understory presented a contribution of 15.85 Mg ha-1 of total biomass and a supply of nutrients corresponding to 0.42 Mg ha-1. It has been found that the nutrients most limiting to productivity in the next cycle will be Potássio, Enxofre and Zinco in harvesting system only the wood. The highest the CUB values were found for P, followed by S> Mg > Ca > K > N. This indicates that, among the evaluated macronutrients, P was used more efficiently for wood production. The wood compartment had the highest coefficient of biological utilization of nutrients. Furthermore, the collection of all above-ground biomass system, the entire tree harvesting system and collection system only timber shell, most of the nutrients are limiting, with the exception of Mg and Cu, which may withstand between 3 and 10 rotations, respectively. The system of harvesting only the wood trunk allowed a greater number of rotations than the other systems, being thus more sustainable to maintain the fertility of the soil. The RMa - Ca management system was the one that obtained less export of nutrients and less removal of biomass from the site, which makes this harvesting system the most suitable for maintaining the nutritional sustainability of the site. Therefore, the management of the waste must be taken into account by the company, so that it can guarantee the nutritional sustainability of the soil, and consequently the productivity of the next rotations.