Management of forest harvest residues affects soil nutrient availability during reforestation of Eucalyptus grandis

Maintaining Eucalyptus harvest residues on site contributes to forest soil productivity and system sustainability, but in temperate climate slow decomposition of residues left on the soil surface limits the amounts of recycled nutrients available for future reforestation. In this work, decomposition rates (k) of the different fractions of Eucalyptus grandis residues left on the soil surface or incorporated into the soil (buried) by tillage were quantified. Thus, the potential rate of nutrient release was determined for N, P, K, Ca, Mg, and the effect on the growth of E. grandis after reforestation. Biomass decomposition and nutrient release profiles (3, 6, 9, 12, 18, 24 and 30 months) were determined for both left on soil surface and buried residues. Tree diameter at breast height (DBH), total height, and nutrient content in leaves were determined in young trees. Each buried residue had a higher k than the corresponding left on soil surface residue with 79 and 47 % biomass loss, respectively. On average, the effect of burial decreased decomposition half-lives from 3.5 to 1.2 years. Potassium recycling was rapid through the period, while Ca release (bark, branches) increased in the last 6 months. Residue burial increased N, P, K, Ca and Mg release by 22, 26, 5, 20 and 13 %, respectively; in addition, it improved soil quality by both increasing exchangeable cations and decreasing soil acidity. Although Ca and Mg concentrations in leaves after reforestation (second turn plantation) increased with residue incorporation, the treatment with residue removal presented significantly higher DBH and height.