Potential contribution of eucalypt harvest residues to soil organic carbon in Brazil

Abstract

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 (t_0.5). For HR − B, net increments in C₃-SOC within the PSF > 53 µm increased significantly with HR t_0.5, regardless of soil disturbance. Otherwise, the C₃-SOC content within the PSF < 53 µm increased with HR t_0.5 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.