Changes in nematode communities following cultivation of soils after fallow periods of different length

The composition of the nematofauna was studied in four soils that differed in length of fallow restoration period since previous cultivation. The longest fallow period was 21 years. Plots were sampled for 2 years after starting cultivation of the fallow soils. The treatments were ranked following a restoration-exploitation gradient depending on fallow duration and the number of years of millet cultivation after fallow clearing ; components of the nematofauna were analysed for correlation with this ranking. The nematode community structures at the first date of sampling during cultivation clearly reflected the length of the fallow period. Nematode community structures in the fallow soils rapidly approached those in the continuously cultivated soil ; they were hardly distinguishable during the second year of cultivation. One-third of the recorded nematode taxa exhibited pronounced responses to the cultivation. Mononchidae, Anatonchidae, Tylencholaimoidea, #Acrobeles$, #Pseudacrobeles$, Tylenchidae and #Helicotylenchus$ preferred sites of more mature successional status, while Dorylaimoidea, #Tylenchorhynchus$ and Rhabdolaimidae dominated the cultivated sites. The maturity index (MI) did not distinguish the management regimes. The plant parasite index (PPI) tended to decrease with higher restoration status linked to greater abundance of the Tylenchidae in these situations. The decrease of fungal to bacterial feeders reflected a decreasing importance of the fungal decomposition pathway after resuming cultivation. (Résumé d'auteur