Combined effect of trees and soil fertility management practices on millet yields in the Sahel

Tree/shrub species are used in farmer fields of sahelian agroforestry parklands to conserve and restore degraded lands, improve soil fertility and increase crop yield. A field study was conducted to investigate the effect of five tree species ( Annona senegalensis , Balanites aegyptiaca , Faidherbia albida , Guiera senegalensis and Piliostigma reticulatum ) on soil fertility and crop yield under different fertility management practices in semi-arid Niger. Three factors (tree species, positions to tree trunk and fertilizer management) and four levels of fertilizer microdosing management (DAP, NPK, manure and control) were investigated. We found that tree species improved soil fertility and crop yield differently. F. albida , improved the soil quality far better than other four tree species for all soil nutrients analyzed. The highest millet yield was recorded under P. reticulatum and F. albida for both grain (1011 and 1005 kg ha −1 , respectively) and straw yields (3662 and 3786 kg ha −1 , respectively). The yield was found to be two- to four-folds higher under direct tree crown compared to close neighborhood or treeless outside. The combined tree species and fertilizer effect were additive and the positive effect can extend to the outside crown. However, the combined effect of mineral fertilizer with tree species on yield was better than that of manure. Integrated tree species and moderate fertilizers was effective and can be used as a sustainable fertility management practice in Sahelian countries where organic amendment is frequently scarce and it is difficult for smallholder farmers to adopt high recommended mineral fertilizer for crop production. Further investigations are needed to assess the economic performance and the long-term sustainability of the integrated trees and soil fertility management in the Sahel.