Indices of nematode community structure and labile soil organic matter fractions used for the assessment of biologically-based fertility

Background/Question/Methods . In this work, we evaluated the use of functional and family level descriptors of nematode community composition to better understand the nematode-resource association and to design appropriate soil testing strategies for biologically-based fertility. Soil samples were collected from an organic research trial in Champaign, IL that included pasture-, row crop-, and vegetable-based systems treated with cover crops alone or with either compost or manure. Soil samples were collected during a three year period for nematode trophic identification, and the computation of the nematode Maturity (MI), Plant Parasitic (PPI), Enrichment (EI), Channel (CI), and Structure (SI) indices. Samples were also analyzed for active fractions of soil organic matter (SOM) including particulate organic matter-C and –N (POM-C, POM-N), particulate organic matter C:N ratio (POM C:N), potentially mineralizable N (PMN), Illinois-N (IL-N), and microbial enzymatic activity (FDA).

Results/Conclusions . Results showed that concentrations of all variables fluctuated within seasons and were generally higher in the pasture- and manure-based plots than in the other management scenarios. Proportional abundances of nematodes also varied with management. Bacterial feeding nematodes dominated the communities early in the course of this study, while plant parasitic nematodes became dominant over time. The decline in abundances of bacterial feeding nematodes probably means that nematode contributions to N mineralization also declined. Multivariate analysis found associations of bacterial feeding nematodes with labile fractions of SOM, and plant parasitic nematodes, predators, and omnivorous nematodes with soil moisture and bulk density. In the last year of the study, canonical discriminant analysis and stepwise selection revealed that indices of nematode community structure and SOM fractions were able to differentiate soil quality in the pasture from the row crop and vegetable production systems. The EI indicated nutrient enrichment in the pasture system and was related to higher concentrations of SOM fractions. The bacterial decomposition pathway, described by low CI values, dominated the pasture system and became less dominant in the late summer and fall months. A drop in SI values after soil preparation and an increase in the PPI suggested disruption of the nematode community. Soil sampling and analysis on at least two sampling occasions can provide insight into the dynamic status of the soil community and resource availability. The statistical approach used for identification and selection of sensitive indicators revealed nematodes were more sensitive to management than were SOM fractions. This information is critical to design and recommend soil testing strategies in organic farming systems.