Melo V. S. auteur aut IRD Desjardins Thierry auteur aut IRD Silva M. L. auteur aut IRD Santos E. R. auteur aut IRD Sarrazin Max auteur aut IRD Santos M. M. L. S. auteur aut IRD text journalArticle eng text/pdf born digital access The main change in soil use in Amazonia is, after slash and burn deforestation followed by annual crops, the establishment of pastures. This conversion of forest to pasture induces changes in the carbon cycle, modifies soil organic matter content and quality and affects biological activity responsible for numerous biochemical and biological processes essential to ecosystem functioning. The aim of this study was to assess changes in microbial biomass and activity in fallow and pasture soils after forest clearing. The study was performed in smallholder settlements of eastern Brazilian Amazonia. Soil samples from depths of 02, 25 and 510 cm were gathered in native forest, fallow land 810 yr old and pastures with ages of 12, 57 and 1012 yr. Once fallow began, soil microbial biomass and its activity showed little change. In contrast, conversion to pasture modified soil microbial functioning significantly. Microbial biomass and its basal respiration decreased markedly after pasture establishment and continued to decrease with pasture age. The increase in metabolic quotient in the first years of pasture indicated a disturbance in soil functioning. Our study confirms that microbial biomass is a sensitive indicator of soil disturbance caused by land-use change. specialized Soil microbial carbon microbial basal respiration metabolic quotient tropical soil deforestation land use AMAZONIE BRESIL PARA ETAT 082 074 068 28 4 530-535 2012 0266-0032 https://www.documentation.ird.fr/hor/fdi:010058249 10.1111/sum.12003 0266-0032 [F B010058249] https://www.documentation.ird.fr/hor/fdi:010058249 https://www.documentation.ird.fr/intranet/publi/2013/01/010058249.pdf Accès réservé (Intranet de l'IRD) IRD - Base Horizon / Pleins textes 2013-02-06 2017-08-23 fdi:010058249 fre