Potential contribution of eucalypt harvest residues to soil organic carbon in Brazil
2020
Souza, Ivan F. | Barros, Nairam F. | Novais, Roberto F. | Vergütz, Leonardus | Silva, Ivo R.
The extent by which the contribution of eucalypt harvest residues (HR) to soil organic carbon (SOC) is impacted by soil disturbance during and/or after harvesting is unclear. We addressed this question by following the decomposition of HR in microplots (15-cm diameter, 15-cm height) and determining their contribution to SOC in 10 sites across southeastern Brazil. The experiment was set up according to a complete randomized block design arranged into a 3 × 2 factorial scheme including: HR removal (HR₀), only bark removal (HR − B) and HR including bark (HR + B) applied to: undisturbed soil (US) with HR left on the soil surface or disturbed soil with HR mixed into the first 5 cm of the topsoil. We had eight blocks as replicates. Following a 12-month field decomposition, soil samples were fractionated to isolate SOC within the particle-size fractions (PSF) greater and lower than 53 µm. Subsequently, we used ¹³C to quantify the effects of the treatments in C₃-derived SOC content (C₃-SOC) within each PSF. For both PSF, their C₃-SOC content increased in response to HR − B or HR + B relative to HR₀, depending on soil disturbance and HR half-life time (t₀.₅). For HR − B, net increments in C₃-SOC within the PSF > 53 µm increased significantly with HR t₀.₅, regardless of soil disturbance. Otherwise, the C₃-SOC content within the PSF < 53 µm increased with HR t₀.₅ in response to both HR types, but only for US treatments. Overall, in regions where climate drives fast decomposition rates, on-site disturbance during and/or after harvesting should be minimized to favor the contribution of HR to SOC, particularly within the PSF < 53 µm.
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