Interpretation of nematode community indices requires a reference to a rela
tively undisturbed community. Maturity and trophic diversity index values w
ere compared for five pairs of certified organically and conventionally man
aged soils in the Piedmont region of North Carolina. Available nitrogen (ni
trate, ammonium) was estimated at various lag periods relative to times of
sampling for nematode communities to determine the strength of correlative
relationship between nematode communities and nitrogen availability. Soils
were sampled six times yearly in 1993 and 1994 to determine the best time o
f year to sample. Maturity values for plant parasites were greater in organ
ically than conventionally managed soils, and differences between managemen
t systems were greater in fall than spring months. However, other maturity
and diversity indices did not differ between the two management practices.
Differences in crop species grown in the two systems accounted for most dif
ferences observed in the community of plant-parasitic nematodes. Indices of
free-living nematodes were correlated negatively with concentrations of am
monium, whereas indices of plant-parasitic nematodes were correlated positi
vely with concentrations of nitrate. Due to the similarity of index values
between the two systems, organically managed soils are not suitable referen
ce sites for monitoring and assessing the biological aspects of soil qualit
y for annually harvested crops.