Effect of fallow improvement on the nematode community in the Sudanian region of Senegal

A 4-year trial was conducted in the Sudanian area of Senegal to study how the manipulation of the plant composition of a natural fallow might increase soil fertility. The influence of fencing combined with stump removal or planting of Andropogon gayanus on the nematode communities was studied. Apart from fencing, all intervention favoured the multiplication of the plant parasitic nematodes for the duration of the trial. Fencing significantly reduced nematode abundance and modified the balance between the species in the community. The population of Scutellonema cavenessi, a serious pest of food crops in the region, was dramatically reduced to the benefit of the weaker pathogen, Helicotylenchus dihystera. Planting Andropogon increased the H. dihystera population slightly. Disappearance of ligneous plant material by stump removal was associated with the greatest increase in the proportion of S. cavenessi. The results suggested that the soil disturbance when planting, removing stumps, or even grazing could affect the nematode community in the topsoil layer, resulting in a decrease in H. dihystera. This species did not recover during a 4-year fallow, even if a suitable situation was promoted through fencing or the planting of Andropogon, a host plant of H. dihystera.