Bioremediative management of soybean nematode population densities in croprotations with velvetbean, cowpea, and winter crops

A field microplot trial was established to evaluate nematode population dyn amics in a rotation program utilizing nematode-suppressive and non-suppress ive legumes, and nematode-host and nonhost grass species. The rotation trea tments consisted of velvetbean (Mucuna deeringiana) or cowpea (ligna unguic ulata) during the first year, followed in winter by oat (Avena sativa), whe at (Triticum aestivum), rye (Secale cereale), rye grass (Lolium sp.), clove r (Trifolium sp.), hairy vetch (Vicia villosa), lupine (Lupinus sp.) or fal low. Rotation in the second and third year consisted of soybean (Glycine ma x). Results showed that velvetbean had a generally suppressive effect on po pulations of root-knot (Meloidogyne incognita), cyst (Heterodera glycines), and stunt (Tylenchorhynchus claytoni) nematodes in soil and roots. It had little effect on populations of Helicotylenchus dihystera. Velvetbean rotat ions with winter grass species were also effective in reducing nematode pop ulation densities in soil. Soybean yields were positively correlated with v elvetbean in rotations with winter grass species. High populations of M. in cognita were negatively correlated with soybean yields. The use of velvetbe an as a rotation crop assures reduction of important plant-parasitic nemato des in soil and an improvement in soybean yield.