Stability of elemental carbon in a savanna soil

(W)e have investigated the stability of oxidation-resistant elemental carbon (OREC) in a sandy savanna soil at the Matopos fire trial site, Zimbabwe. The protection of some soil plots from fire for the last 50 years at this site has enabled a comparison of OREC abundances between those plots which have been protected from fire and plots which have continued to be burnt. The total 0-5 cm OREC inventory of the soil protected from fire is estimated to be 2.0+/-0.5 mg cm(-2); approximately half the "natural" OREC inventory at the study site of 3.8+/-0.5 mg cm(-2) (the mean for plots burnt every 1-5 years). The associated half-life for natural OREC loss from the 0-5 cm interval of the protected plots is calculated to be 2000 mu m) in the soil being considerably 2 and subsequently emitted from the soil, reduced to a sufficiently small particle size to be illuviated to deeper parts of the soil profile, solubilized and lost from the profile as dissolved organic carbon or transmuted into a chemical form which is susceptible to attack by the acid-dichromate reagent. The conclusion that a significant proportion of OREC can undergo natural degradation in well-aerated environments on decadal/centennial timescales suggests that only a fraction of the total production of OREC from biomass burning and fossil fuel combustion is likely to be sequestered in the slow-cycling "geological" carbon reservoir. [References: 30