During the past 50 yr, ecological and agricultural scientists have pursued an integrated definition and metric of soil quality. In the past 20 yr, considerable attention has been paid to nematodes, demonstrating that these ubiquitous members of the soil community reflect change in ecological structure and function of soils in ways more predictable and efficient than for other soil flora or fauna. With the help of multivariate analysis, we studied the application of free-living nematode communities as model indicators of physical and chemical disturbance of agricultural soil. We used canonical correspondence analysis (CCA) and partial CCA to segregate effects of tillage and chemical/nutrient treatments. With the results of CCA, we assigned relative direct and indirect tillage sensitivity and chemical/ nutrient sensitivity ratings to soil genera found in two test data sets, each containing three matrices: (1) sites by species or genera, (2) sites by soil properties, and (3) sites by management practices. Of 46 total genera, the ones most sensitive to direct effects of tillage include Aphelenchoides, Eucephalobus, Eudorylaimus, Heterocephalobus, and Wilsonema compared to the tolerant genera Achromadora, Anatonchus, Cephalobus, Chiloplacus, Clarkus, Epidorylaimus, Mylonchulus, Plectus, and Tylencholaimellus. Some genera are more sensitive to indirect than direct effects of tillage: these include Achromadora, Cephalobus, Microdorylaimus, Monhystera, Panagrolaimus, and Prionchulus. With the exception of Discolaimus and Prismatolaimus, genera sensitive to chemical/nutrient treatments differ from those sensitive to tillage treatments including Alaimus, Cylindrolaimus, Mesorhabditis, Odontolaimus, and Protorhabditis. Likewise, genera uniquely sensitive to indirect but not direct effects of chemical/nutrient treatments are Aphelenchus, Aporcelaimellus, and Diplogaster. Eudorylaimus and Eumonhsytera are sensitive to indirect effects of both tillage and chemical/nutrient treatments. Our results suggest that physical and chemical/nutrient disturbances can alter populations of nematode genera differently, and that indirect effects of management are greater than direct effects. This methodology aids in distinguishing nematode genera that have distinctive responses to agricultural management practices from those that are ambiguous. This knowledge is useful for both interpretation and enhancement of free-living nematode community indices.

During the past 50 yr, ecological and agricultural scientists have pursued an integrated definition and metric of soil quality. In the past 20 yr, considerable attention has been paid to nematodes, demonstrating that these ubiquitous members of the soil community reflect change in ecological structure and function of soils in ways more predictable and efficient than for other soil flora or fauna. With the help of multivariate analysis, we studied the application of free‐living nematode communities as model indicators of physical and chemical disturbance of agricultural soil. We used canonical correspondence analysis (CCA) and partial CCA to segregate effects of tillage and chemical/nutrient treatments. With the results of CCA, we assigned relative direct and indirect tillage sensitivity and chemical/nutrient sensitivity ratings to soil genera found in two test data sets, each containing three matrices: (1) sites by species or genera, (2) sites by soil properties, and (3) sites by management practices. Of 46 total genera, the ones most sensitive to direct effects of tillage include Aphelenchoides, Eucephalobus, Eudorylaimus, Heterocephalobus, and Wilsonema compared to the tolerant genera Achromadora, Anatonchus, Cephalobus, Chiloplacus, Clarkus, Epidorylaimus, Mylonchulus, Plectus, and Tylencholaimellus. Some genera are more sensitive to indirect than direct effects of tillage: these include Achromadora, Cephalobus, Microdorylaimus, Monhystera, Panagrolaimus, and Prionchulus. With the exception of Discolaimus and Prismatolaimus, genera sensitive to chemical/nutrient treatments differ from those sensitive to tillage treatments including Alaimus, Cylindrolaimus, Mesorhabditis, Odontolaimus, and Protorhabditis. Likewise, genera uniquely sensitive to indirect but not direct effects of chemical/nutrient treatments are Aphelenchus, Aporcelaimellus, and Diplogaster. Eudorylaimus and Eumonhsytera are sensitive to indirect effects of both tillage and chemical/nutrient treatments. Our results suggest that physical and chemical/nutrient disturbances can alter populations of nematode genera differently, and that indirect effects of management are greater than direct effects. This methodology aids in distinguishing nematode genera that have distinctive responses to agricultural management practices from those that are ambiguous. This knowledge is useful for both interpretation and enhancement of free‐living nematode community indices.

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Samples of agricultural soils were collected across North Carolina in 1992 and Nebraska in 1993 to determine which indices of nematode communities could be applied to distinguish ecological pattern at regional geographic scales. Sampling density was proportional to the area of agriculture in each region of each state. Maturity indices (based on life-history characteristics) were calculated to determine the successional status of nematode communities, and diversity indices were calculated to estimate relative abundance of nematode trophic groups. Population densities of nematode families were also compared between states and among regions within states. The range of maturity-index values for free-living and plant-parasitic nematodes was greater for soils in North Carolina than in Nebraska. The relative distribution of nematode trophic groups (bacterial feeders, fungal feeders, plant parasites, omnivores, and predators) was similar in the two states. Significant differences in maturity-index values for free-living and plant-parasitic nematodes were found between but not within states. We conclude that regional or national assessments of soil ecological condition based on measures of nematode community structure can be made at a geographic resolution of 125 000-200 000 km 2 of land area.