Estimating changes in soil organic carbon storage due to land use changes using a modified calculation method

Carbon sources and sinks have been widely scrutinized over the last ten years as a result of the Kyoto Protocol. In this paper we added a new concept (standardized reference depth, D-SR) to the current calculation method in order to assess and compare the soil organic carbon (SOC) storage changes due to three major land use changes with a certain historical relationship (from primary rain forest to fallow land to natural secondary forest and finally to rubber plantations -Hevea brasiliensis) in a northern tropical ecosystem in southwest China. Over 30 years, the soil organic carbon storage did not decrease significantly with a land use change from primary rain forest to fallow land (approximately 10.3%). However, it did increase significantly (approximately 49.3%) due to conversions to natural secondary forest and rubber plantations (approximately 41.6%). In this region, the soil carbon sequestration at rubber plantations is similar to that of natural secondary forests. Compared with the modified method, the current method overestimated carbon storage on fallow land by 8.8% more than the actual storage (calculated reference depth of 13.9 cm, D-r - D-SR = 13.9, without the reference depth standardization process), overestimated carbon storage at rubber plantations by 3.6% (calculated reference depth of 4.9 cm), and underestimated the natural secondary forest carbon storage by 6.4% (calculated reference depth of 9.7 cm). Thus, the modified process using the standardized reference depth for the current method is necessary for the evolution and comparison of soil carbon or other nutrient storage changes.