| Abstrakt: |
The potential export of nutrients by eucalypt plantations harvest raises concern about environmental and wood production sustainability. Keeping non-commercial components in the field can minimize it. However, little is known about changes in chemistry of decomposing eucalypt harvest residues. Simulated harvest residue management practices fully replicated across 11 Brazilian representative sites were undertaken to evaluate the dynamics of macronutrient release. We studied the influence of de-barking in the field, the use of an external source of nitrogen and the placement of harvest residues (remained on the surface or incorporated into the soil). After the experiment set up, residues were sampled five times and contents of Ca, Mg, N, P, K and S were determined. We used the remaining mass and nutrient concentration to fit the single exponential decay model ( X = X 0 e − kt ) and calculate half-life ( hl = ln(2)/ k ) of each nutrient. At the end, we calculate element ratios to see differences in residue chemistry. The presence of bark and residue incorporation into soil enhanced decomposition and decreased nutrient half-life across all site. External N had little or no effect on nutrient dynamics. Site had significant effect on nutrient half-life, but only low correlations with climate or edaphic properties could be found. C:N, C:S and C:Ca ratios were much narrower at the end. On the other hand, N:P, N:K, Ca:S and Ca:Mg were wider. C:P varied among sites, but averaged almost the same as in the beginning. Ca was the nutrient that presented the greatest immobilization, particularly in the absence of bark, indicating a critical role of this element on decomposition under the conditions tested. Our results suggest that nutrient release is more controlled by management, chemical properties of the residues and specific decomposer community needs than climate or soil properties. Microbial community seems to change their carbon use efficiency and immobilize nutrients in limiting conditions. [ABSTRACT FROM AUTHOR] |
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