AN INITIAL STUDY OF FALLOW PERIODS ON THE NEMATODE COMMUNITY IN THE SOUDANESE-SAHELIAN ZONE OF SENEGAL

Observations were made on natural fallow areas, disturbed by human act ivity, located on shallow ferruginous soils in the Nioro du Rip region , Southern Senegal. Twelve important plant-parasitic nematodes occur i n this region. Size of nematode populations and number of species decr eased with the increase of the fallow period from 1-17 years. When hum an interference was prevented by fencing for the last 5 years of a 17 year fallow, the number of nematodes decreased at a slower rate than i n an unfenced fallow and the number of species increased. Only Helicot ylenchus dihystera and Tylenchorhynchus gladiolatus develop similarly under both conditions. Xiphinema parasetariae occurred mainly in older fallows whilst Scutellonema cavenessi was rare. Numbers of these harm ful plant-parasitic species were reduced by fencing. Saprophyte popula tions remained stable under natural fallow conditions, but increased i n the fenced area, especially associated with the greater deposition o f organic matter near the woody plants. Amongst plant species, Andropo gon pseudapricus, in contrast to Pennisetum pedicellatum, was usually associated with large nematode populations.