Root litter decomposition in a Sub-Sahelian agroforestry parkland dominated by Faidherbia albida

Inagroforestry systems, fine roots grow at several depths due to the mixture of trees and annual crops. The decomposition of fine roots contributes tosoil organic carbonstocks and may impactsoil fertility, particularly in poor soils, such as those encountered in sub-Sahelian regions. The aim of our study was to measure the decomposition rate of root litter from annual andperennialspecies according to soil depth and location under and far from trees in a sub-Sahelian agroforestry parkland. Soil characteristics under and far from the trees were analysed fromtopsoilto 200cm depth. Faidherbia tree,pearl milletand cowpea root litter samples were buried in litterbags for 15 months at 20, 40, 90 and 180cm depths. Rootlitter decompositionwas mainly impacted by soil moisture and soil depth. Faidherbia decomposed more slowly (36±12% remaining mass after 15 months) than cowpea and pearl millet roots (23±7% and 29±11% respectively). Pearl milletaboveground biomass, at harvesting time, was twice as high under (992gm−2) than far (433gm−2) from the tree, andbelowground biomass(0–200cm of depth) was 30.9gm−2and 19.6gm−2under and far from the tree, respectively. Faidherbia fine roots contributed slightly (p-value < 0.1) to higher stocks of C under the tree (7761±346gm−2) than far from it (5425±558gm−2) and from 0cm down to 200cm depth.