Quantificação e modelagem do conteúdo de nutrientes na biomassa aérea de bracatinga (Mimosa scabrella Bentham)

Abstract

The aims of this dissertation were to quantify and to modelling the nutrients in aboveground biomass for Mimosa scabrella Bentham under different site, age and diameter classes. The data for this research came from 25 trees sampled into native Mimosa scabrella stands of the northern Curitiba metropolitan region, Paraná State, Brazil. The trees were cut down and their components were separated in: leaves, twigs, branches, stem wood and bark. Then, a sample of each component was taken to obtain dry matter. Later on, chemical analysis was proceeded to determine N, P, K, Ca, Mg, Fe, Mn, Cu, Zn concentrations for each tree component. To evaluate tree component, site, age and diameter effects over nutrient concentrations and nutrient contents, a completely random experimental design was used, where the statistical analysis was constituted by Bartlett’s test, analysis of variance and Tukey’s test. Several mathematical models were fitted intending to obtain nutrient content estimates for different tree components using tree dimensions, being them: traditional volume models found in the literature, mathematical models specifically built for this work and built by stepwise procedure. The results found in this research indicated that the major of nutrient concentrations presented a decreasing order relative to different tree component as follow: leaves > stem bark > twigs > branches > stem wood. In a general way, the decreasing order of nutrient concentration for the major of tree components was: N > Ca > K > Mg > P > Mn > Fe > Cu > Zn. Considering stie, age and diameter effects over nutrient concentrations, only the site classes showed a significant and coherent influence over some nutrient concentrations. It was verified that P and K leaf concentrations increased with site quality. The nutrient content of the stem wood presented the largest quantity of nutrients, but if firewood of Mimosa scabrella was considered, it owns 70% of total above-ground biomass nutrient content. It turns clear the great Mimosa scabrella stands potential of nutrient losses at crop (harvest). For the nutrient content in the tree components, only the diameter classes presented a significant and coherent influence. The nutrient content increases with the diameter classes. Perhaps, better results of the the site, age and diameter effects over nutrient concentration and content could be found if more trees and stands had been sampled, or with a severe control of the site, age and diameter interrelationships. In a general way, the macronutrient contents were well correlated with tree dimensions, and acceptable equations were derived. However, the same did not occur to the micronutrients, except for Cu and Fe for some tree components. Generally, nutrient content equations presented better performances to the bole components and to the added tree components (leaves + twigs, firewood and total above-ground biomass). In some cases, the insert of bole and crown dimensions, age and dominant height as independent variables improve the nutrient content equations.