Extracción y reciclaje de elementos nutritivos por cosecha de Eucalyptus globulus en Uruguay Nutritious elements extraction and recycling at harvest of Eucalyptus globulus in Uruguay

SUMMARY Eucalyptus commercial plantations extract high quantities of nutritious elements, although the proportion exported after harvest is relatively low. The aims of the work were: a) To quantify the concentration and distribution of nutritious elements in different components of a Eucalyptus globulus harvest b) To quantify decomposition rates of the harvest residues through the time, and the potential recycling of nutritious elements to the soil. In a 10 year-plantation on a Typic Hapludert, 24 trees with average height and DBH were harvested. The aerial biomass and total extraction of nitrogen, phosphorus, potassium, calcium and magnesium of logs, branches, bark and leaves were measured. For 24 months the decomposition of residues was measured with periodical samplings. The debarked commercial logs represented 77.5 % of the produced biomass; and the proportions of nutritious elements exported with them were 32, 45, 19, 18 and 33 % of nitrogen, phosphorus, potassium, calcium and magnesium respectively. The highest concentrations of nutritious elements were found in leaves and bark. The average residue decomposition was 30 % of the initial aerial biomass. Leaves lost the highest proportion of biomass (68 %) and nutritious elements over 24 months, whereas the bark was the most resistant to decomposition. Potassium was released from the residues faster than the others, whereas calcium showed the lowest loss. Nitrogen, phosphorus and magnesium decreases were more gradual, proportional to the decomposition rates. De-barking in the site avoids the exportation of important amounts of nutritious elements.