Biomassa e nutrientes em plantios de eucaliptos no bioma Pampa

Abstract

The silviculture with exotic species is present in most Brazilian s Biomes. In the Pampa Biome RS, although historical records indicate the presence of eucalyptus since 1835, commercial plantations in the southwest of the state for industrial purposes have received the largest investments since 2000. For being an eucalyptus rapid growth and consequently high biomass production and nutrient accumulation, debates are always being provoked to discuss the impacts and sustainability of culture. Given the importance of this scene this study aimed to characterize nutritionally stands of Eucalytpus grandis, Eucalyptus dunnii and hybrid of Eucalyptus urophylla x Eucalyptus grandis (E. urograndis), with four years and six months age, and contribute to the adequacy of nutritional management in eucalypt plantations in Pampa Biome region. The soil in the study area is rated as Ultisol. Three sample units of 10 ha were surveyed and inventoried, one unit for each species, where a total of 27 trees (9 trees per species), sectioned into compartments, sampling were felled for determination of tree biomass and nutrient contents. Planting with E. urograndis showed higher biomass (158.1 Mg ha-1), followed by E. grandis (136.7 Mg ha-1) and E. dunni (121.9 Mg ha-1), with an average distribution to compartments 66% wood, 15% root, branch 9%, 7% bark and 4% leaf. The total stock of nutrients in biomass (macro and micro) was: E. urograndis - 1232 kg ha-1 and 26 kg ha-1; E. grandis - 1289 kg ha-1 and 48 kg ha-1; E. dunnii - 1213 kg ha-1 and 61 kg ha-1, respectively. The largest stock of N was found in leaves to E. grandis and E. dunnii, and steam to E. urograndis. With the harvesting of stem wood, 63% N, 70% P, 47% K, 91% Ca, 73% Mg, 34% B and 46% S, 41% Cu, 38% Fe, 87% Mn, 38% Zn, are returned to the soil by the other biomass components and provides the lowest nutrient removal system. Nutrient removal, on average, according to the scenario of harvest showed the following distribution trend: Wood Steam over Bark + Crown and the Steam over Bark Ca > K > N > Mg > S > P, only Wood Steam K > N > S > Ca > Mg > P, for micronutrients in all scenarios harvest Mn > Fe > Zn > B > Cu. These species showed the same magnitude of biomass allocation in different components (stem wood > root > branch > bark > leaf). E. urograndis had the highest wood production as well as efficiency in using nutrients. P was the element that provided better nutritional efficiency by species. K and S were the elements that presented the greatest risk of productivity limiting, based on the removal of nutrients in different scenarios of biomass harvesting, nutrient balance and potential number of rotations.