Nematode population and community dynamics in soybean-wheat cropping and tillage regimes.

The nematode community structures of various soybean-wheat regimes and of a single-cropped, conventionally tilled soybean regime were studied at two sites in Tennessee. Each of the 100 nematode species identified in the study was placed in one of five trophic groups, the most diverse being plant parasites (31 species), followed by Dorylaimida (26 species), bacterivores (23 species), fungivores (15 species), and predators (5 species). No significant differences in overall diversity and dominance among treatments and trophic groups were found. Densities of Heterodera glycines Ichinohe infective juveniles were significantly higher in single-cropped, conventionally tilled soybeans in July. When data were subjected to ordination analysis, it was shown that plant-parasitic nematode communities produced an aggregation of conventionally tilled, single-cropped soybean plots when compared to all double-cropped treatments. Ordination of overall nematode communities yielded similar results.