Soil organic carbon pools of two tropical soils inferred by carbon signatures

Labile and stable soil organic carbon (SOC) pools of two tropical soils of Belize, Central America, as influenced by land use management, were investigated using a combination of C-14 and C-13 techniques. The sizes and mean residence times (MRT) of the labile pools were found to be in the range of 1.5 to 59.8 g/kg and 5 to 8 yr, respectively, and those of the stable SOC pools, 25.1 to 65.2 g/kg and 250 to 388 yr, respectively. Both the labile and stable SOC pools have significantly shorter MRT than those of the temperate soils. The labile SOC pools of sugarcane (Saccharum officinarum L.) in continuous management averaged 12.9 and 19.8 g/kg, respectively, for Xaibe (Lithic Ustropept) and Louisville (Typic Pellustert) soils. Continuous sugarcane management reduced the labile pool to about one-third the size of the corresponding secondary forests. The labile SOC pool is sensitive to changes in management practices and its size represents the intrinsic sustainable soil productivity. A radiocarbon single-plot approach to study the dynamics of SOC pools was developed using the C-14 and C-13 signatures of the soil and those of the CO2 evolved. The results of the single-plot method and that of the paired-plot method agree well within the range of the experimental errors.