No significant differences in soil organic carbon contents along a chronosequence of shrub willow biomass crop fields

Shrub willow biomass crops (SWBC) have been developed and promoted for widespread deployment in northeastern and mid-western US as well as in Europe. There are concerns that the production system could reduce the soil organic carbon (SOC) over time due to soil disturbances and repeated three-year harvest cycles. This study assesses changes in SOC beneath shrub willow (Salix x dasyclados [SV1]) biomass crops utilizing a 0, 5, 12, 14, and 19-year old SWBC fields. The sitesʹ management history was similar, suggesting uniform SOC contents prior to plantation establishment. SOC contents were analyzed by total (i.e. 45 cm) and by layer (i.e. 0–15 cm, 16–30 cm, and 31–45 cm) across different ages. Mean SOC contents to 45 cm depth ranged from 175 to 188 Mg ha−1, and showed no statistically significantly differences across ages (p = 0.15) and no interaction between age and depth (p = 0.19). SOC contents differed significantly with soil depth when averaged across ages (p < 0.0001). Statistical analysis of SOC contents by layer, however, showed that SOC contents in the upper 15 cm depth were significantly different (p < 0.001). Linear contrasts of mean SOC contents for the 0–15 cm depth revealed that the 0-year old was significantly different compared with the 5, 12, 14, and 19-year old SWBC.