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Decomposition of Eucalyptus sp. and Pinus taeda Harvest Residues under Controlled Temperature and Moisture Conditions

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Document pages: 18 pages

Abstract: Background: Following the harvest of Eucalyptus grandis Hill ex Maiden, Eucalyptus globulus Labill, Eucalyptus dunnii Maiden and Pinus taeda L. forests, an important proportion of the aerial biomass is left to decompose on the site. The decomposition process is known to alter the dynamics of nutrients in the soil, particularly N, which is essential for the growth of the next turn of the plantation. The decomposition of E. grandis, E. globulus, E. dunnii and P. taeda harvest residues (leaves needles, twigs and bark) was studied, following individual incubation of each residue type for 6 months under controlled temperature and humidity. Net N mineralization was also determined. Chemical characteristics of the residues were tested to identify those that affect the rate of decomposition and N release. Results: The highest decomposition rates were found for Eucalyptus leaves and P. taeda needles, but the proportion of C respired by P. taeda needles was lower than that of Eucalyptus leaves. No differences among species were found in the amount of CO2 produced during incubation of twigs. The lowest decomposition rates corresponded to Eucalyptus bark. Although C loss was related to many residue characteristics, the closest relationship was observed with their C:N ratio. Higher amounts of mineral N were produced by decomposition of E. grandis and E. dunnii leaves than P. taeda needles and E. globulus leaves. Bark decomposition produced N immobilization, irrespective of the species, and for twigs, this was also true, except for P. taeda. The net N mineralization by decomposition of Eucalyptus residues was highly correlated with their total N content and the C:N and lignin:N ratios. Conclusion: The total N content and the C:N ratio of residues can be used to satisfactorily assess the decomposition and net N mineralization potential of different residues types, avoiding the need to conduct more complex determinations.

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