Transport of free-living nematodes by runoff water in a Sudano-Sahelian area

The impact of runoff on transport of nematodes was studied using simulated rainfall at Thysse Kaymor, in the Sudano-Sahelian area of Senegal. Three 30 min, 60–75 mm rainfalls were applied every 2 days on three different plots. One plot was previously uncultivated (fallow) and the other two had been planted with groundnut and millet during the previous rainy season. A previous paper by Cadet et al. (2002) reported the results of studies on soil erosion, plant-feeding nematode composition and total free-living nematode density in runoff water, while this paper focuses on the structure of the free-living nematode fauna. The relative abundances of the different taxa of free-living nematodes in runoff water were very different from those found in the 0–10 cm top soil layer. Rhabdolaimus, Aphelenchina, Tylenchidae, free-living Ditylenchus, Rhabditidae and certain Cephalobidae were more numerous in the runoff water than in soil as estimated from the amount of eroded soil. Rhabdolaimus was the most abundant nematode in runoff waters from the groundnut and millet plots where it represented more than 50% of the nematode fauna. In the fallow plot, the most abundant nematode in runoff water was Ditylenchus. The over-representation of some taxa in runoff water was linked to their greater motility and to their greater abundance in the superficial layer of soil.