Horizon 1 1 17 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES European Journal of Soil Science 876-885 GUYANE FRANCAISE ZONE TROPICALE HUMIDE 2015 fdi:010065247 ENG European Journal of Soil Science 1351-0754 ISI:000361187000006 5 10.1111/ejss.12277 https://www.documentation.ird.fr/hor/fdi:010065247 https://www.documentation.ird.fr/intranet/publi/depot/2015-10-08/010065247.pdf 66 Horizon (IRD) Large inputs of woody debris to soil can improve the soil. We examined the fate of woody debris buried in soil after fire-free forest conversion to cropland in French Guiana. We measured the mass loss of woody debris >4mm on five sampling dates for 4years after deforestation. Composition of the organic matter of woody debris was analysed with Rock-Eval pyrolysis, which enabled us to distinguish a labile carbon pool (C-lab) and a resistant carbon pool (C-res). Decomposition of woody debris followed a first-order function with a half-life of 17.6months. During the decomposition of woody debris >4mm, the C:N ratio, hydrogen index (HI) and pyrolysed carbon below 400 degrees C (R400) decreased, suggesting that decarboxylation and dehydrogenation of woody debris occurred. Both C-lab and C-res stocks decreased with time, but the decrease in C-lab was faster. There was little humification of the debris and no long-term biogeochemical preservation of a woody debris fraction, which accords with the first-order decay observed. We conclude that the benefits of ligno-cellulosic inputs for soil organic carbon contents in a tropical humid climate occur during the first year following deforestation. 068 ; 064 UR210 / US122