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

Abstract: In agroforestry systems, fine roots grow at several depths due to the mixture of trees and annual crops. The decomposition of fine roots contributes to soil organic carbon stocks and may impact soil 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 and perennial species 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 from topsoil to 200 cm depth. Faidherbia tree, pearl millet and cowpea root litter samples were buried in litterbags for 15 months at 20, 40, 90 and 180 cm depths. Root litter decomposition was 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 millet aboveground biomass, at harvesting time, was twice as high under (992 g m−2) than far (433 g m−2) from the tree, and belowground biomass (0–200 cm of depth) was 30.9 g m−2 and 19.6 g m−2 under and far from the tree, respectively. Faidherbia fine roots contributed slightly (p-value < 0.1) to higher stocks of C under the tree (7761 ± 346 g m−2) than far from it (5425 ± 558 g m−2) and from 0 cm down to 200 cm depth