Nematode communities and microbial biomass in soils with annual and perennial crops

Soils from medium- (alfalfa) or long-term (tall-fescue pasture) perennial cropping systems, which represent systems with relatively little disturbance, were collected across the three geographic regions of North Carolina and evaluated as potential reference sites for monitoring the ecological condition of soils for annual crops (e.g. soybeans). Maturity (based on life history characteristics) and trophic diversity indices of soil nematode communities were quantified for all soils to determine the successional status and relative abundance of trophic groups, respectively, in agricultural soils. The distribution and range of maturity index values for plant-feeding nematodes were greater for perennial than annual crops. The relative distribution of nematode trophic groups (bacterial-feeders, fungal-feeders, plant-feeders, omnivores, and predators) was similar among annual and perennial cropping systems. The ratios of fungal-feeding to bacterial-feeding nematodes were greater in perennial than annual cropping systems indicating that the decomposition pathway was dominated more by fungi and fungal-feeding nematodes in alfalfa and pastures than soybean cropping systems. Ratios of total fungal- to total bacterial-biomass were greater for pasture and soybean than for alfalfa cropping systems and, therefore, did not clearly differentiate perennial and annual crops. Based on the maturity index for plant-feeding nematodes, and the ratio of fungal-feeding to bacterial-feeding nematodes, fields with alfalfa or in pasture may be suitable for use as reference sites in monitoring the ecological condition of soil associated with annual crops for the Agroecosystem component of the Environmental Monitoring and Assessment Program (EMAP ), a national monitoring program initiated and sponsored by the U.S. Environmental Protection Agency.