Jaiarree, S.;Chidthaisong, A.;Tangtham, N.;Polprasert, C.;Sarobol, E.;Tyler, S. C.

Faculty of Agriculture, Kasetsart University, Bangkok 10900 (Thailand);Faculty of Forestry, Kasetsart University, Bangkok 10900 (Thailand);Joint Graduate School of Energy and Environment, King Mongkuts University of Technology Thonburi, Bangkok 10140 (Thailand);Department of Chemistry, Norco College, Norco, CA 92860-2600 (USA);Sirindhorn International Institute of Technology, Thammasat University, Pathum Thani 12121 (Thailand)

aerial photography;carbon;composition;conversion;cultivation;forests;land use;maize;maps;organic carbon;photography;site selection;soil;soil chemistry;soil organic matter;soil science;surveys;zea mays;zea;poaceae;cyperales;monocotyledons;angiosperms;spermatophyta;plants;eukaryotes;apec countries;asean countries;developing countries;south east asia;asia.

Soil organic carbon (SOC) content and its stable carbon isotopic composition (within the upper 1 m) were measured to determine the effect of land-use changes from dry evergreen forest to maize fields in eastern Thailand. Digital land cover maps, derived from aerial photography and satellite images for years 1989, 1996, and 2002 were used in association with field surveys and farmer interviews to derive land-use history and to assist in study site selection. Conversion from forest to maize cultivation for the duration of 12 years reduced SOC stocks at the rate of 6.97 Mg C ha^-1 year^-1. Reduction was most pronounced in the top 10 cm soil layer, which was 47% after 12 years of cultivation. Stable carbon isotope data revealed that the main fraction lost was forest-derived C. Generally low input rates of maize-derived C were not sufficient to maintain SOC at the level prior to forest conversion. After 12 years of continuous maize cultivation, the maize-derived C fraction made up about 20% of total SOC (5 Mg ha^-1 of the total 25.31 Mg ha^-1).