Soil carbon sequestration potential of willows in short-rotation coppice established on abandoned farm lands

Aims: We carried out a paired-site study (Melanic Brunisol) to assess the impact on soil carbon stocks of land-use change following establishment and multiple rotations of willows (Salix miyabeana SX67) in short-rotation coppice (SRWC). Methods: Total soil organic carbon (TSOC), hot-water extractable carbon (HWC) and amino sugars (AS) were used as main parameters of soil carbon dynamic. Results: We found that the establishment event and 2 years of growth under SRWC did not result in any change in the TSOC pool or in the HWC pool. However, we found an increase in AS at and near the soil surface (0-20 cm) of the establishing willow plantations. We related this to the effect of the green manure applied before planting. After multiple rotations of SRWC, we found a redistribution of TSOC in the vertical profile (0-40 cm) but no TSOC difference compared to previous land-use (abandoned alfalfa crop). In the subsoil (20-40 cm), we found indications that the more labile soil organic carbon (SOC) pools were depleted (HWC and muramic acid). Conclusions: Willow plantations on Melanic Brunisol in southern Quebec (Canada) represent, over the long-term, a soil carbon sink when replacing a short-term no-till crop rotation. However, the conversion from abandoned alfalfa fields into SRWC does not apparently enhance soil carbon potential sequestration.