Quantifying soil organic carbon stocks in herbaceous biomass crops grown in Ontario, Canada

Nineteen farms growing herbaceous biomass crops, switchgrass (Panicum virgatum) and miscanthus (Miscanthus spp.), were sampled for soil organic carbon (SOC) across Ontario, Canada in 2016. Switchgrass and miscanthus fields were sampled in addition to nearby agricultural fields and woodlots to compare SOC in herbaceous biomass systems relative to alternative land-uses. The mean SOC concentration of the woodlots was 4.26 +/- 0.29% and was significantly higher (p < 0.05) than in any other types of land-use. The mean SOC concentration in agricultural fields was 2.21 +/- 0.31%, while switchgrass and miscanthus had a mean SOC concentration of 2.50 +/- 0.29 and 2.50 +/- 0.36%, respectively. The mean SOC stock (0-30 cm) was highest in woodlots at 103.55 +/- 7.40 Mg C ha(-1). This was significantly higher than stocks quantified in agricultural and miscanthus land-uses, which contained 80.51 +/- 7.74 and 83.36 +/- 8.97 Mg C ha(-1), respectively. The mean SOC stock calculated for switchgrass was 85.30 +/- 7.14 Mg C ha(-1) and was not significantly different (p > 0.05) when compared with the SOC stocks quantified for the woodlot. The study recorded numerically higher SOC concentrations and stocks in biomass fields compared to agricultural fields. Therefore, biomass systems contribute to higher SOC sequestration. However, challenges associated with this study such as accurate bulk density measures and lack of baseline data need to be resolved in order to improve quantification of SOC sequestration.