GEEFT

MOST, IRD, ORSTOM, F-34394 Montpellier 5, France; ENGREF, Inst Forestry Agr & Environm Engn, F-34093 Montpellier, France; CIRAD, F-34398 Montpellier, France Article English

Fallowing is a common practice for the management of soil fertility in low-input cropping systems of the West-African savanna, but has been threatened by the growing need for land in the sub-region for the past few decades. Proposals for alternatives to traditional fallowing must rely on a proper understanding of the soil biochemical dynamics occurring after fallow conversion to cropping. Two mesh-bag experiments were thus conducted in two sites (dry and sub-humid tropical climates) in Senegal to assess the role of site-related factors (climate, macrofaunal activity) and root-related factors (tree species, root diameter) on the decomposition of tree roots after clearing of fallow vegetation as measured from mass loss. Root decomposition was fastest - and even faster than predicted from a global model - in the wettest site (first order disappearance rate: 1.00 y(-1) and 1.46-1.49 y(-1) under dry and sub-humid conditions, respectively). Macrofauna accounted for half of root mass loss in the sub-humid site, with biomass removal occurring even during the dry season. Fastest disappearance for roots with phi