Effects of land use change on turnover and storage of soil organic matter in a tropical forest

Aims Land-use change of tropical forests causes loss of soil organic matter and plant productivity. Effects of fallow or plantation vegetation on soil organic matter storage need to be clarified to optimize land-use that maximizes soil organic matter storage and plant productivity. Methods We compared 30-year changes in soil carbon stocks and litter decomposition under different land-uses (primary dipterocarp forest, Macaranga forest, Imperata grassland, transition of Imperata grassland to Acacia plantation, transition of Imperata grassland to oil palm plantation) in Indonesia. Results The Imperata grassland maximizes soil carbon stocks for up to 10 years due to considerable root litter inputs, but additional organic matter storage is limited over the following 20 years, due to high grass litter decomposability in the less acidified soil. The conversion of Imperata grassland to oil palm plantation causes greatest loss of soil organic matter, whereas Acacia plantation on Imperata grassland or the Macaranga forest maximizes soil carbon stocks due to input of recalcitrant forest litters and reduced microbial activities in the acidified soils. Conclusion Farmers could adopt short-term (<10 years) grass fallow or longer-term (>10 years) fallow under Acacia plantation on Imperata grassland or Macaranga regeneration forest to maximize soil organic matter storage. The optimum and feasible land-use strategies should be selected based on the length of fallow period and the original acidity of soil.