Soil Carbon Fractions under Vetiver Grass in Australia and Ethiopia Relative to other Land Uses

The allocation of soil organic carbon (SOC) to its component fractions can indicate the vulnerability of organic carbon stocks to change. The impact of vetiver on the composition and distribution of SOC can provide a complete assessment of its potential to sequester carbon in soil.Purpose: This study quantified the distribution and impact of SOC under vetiver and the allocation of SOC to particulate (POC), humus (HOC) and resistant (ROC) fractions differentiated based on particle size and chemical composition under vetiver grass compared with other plant types.Methods: Carbon fractions were measured on soil samples collected from Australia and Ethiopia to a depth of 1.0 m under three plant communities (vetiver, coffee, and Australian native pastures). We used the MIR/PLSR spectra to estimate SOC fractions based on fractionated, and NMR measured values.Results: The stocks of SOC fractions indicated significant differences in the proportion of labile POC to HOC across sites and vegetation types. The dominant carbon fraction was HOC (71%) for all vegetation types. The average carbon sequestration rate under vetiver for OC was - 2.64 to + 7.69 Mg C ha- 1 yr- 1, while for the POC, HOC and ROC was 0.04 to + 1.17, -3.36 to + 4.64 and - 0.35 to + 1.51 Mg C ha- 1 yr- 1, respectively.Conclusion: Growing vetiver and undisturbed native pastures has on average a high accumulation rate of a more stable carbon (HOC) which is less vulnerable to change, and change was largely driven by the HOC fraction. We, therefore, recommend the use and promotion of perennial tropical grasses like vetiver and similar grasses and undisturbed native pastures as potential options to facilitate soil carbon sequestration.