Nematode Community Structure and Indicators of Biologically-Based Fertility: Influence of Management During Transition to Certified Organic Production

184 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2009.This research investigated the influence of management on indicators of soil quality and nematode community structure in systems transitioning from conventional to organic production. The goal was to improve soil assessment and ultimately performance of organic production systems. Soil samples were collected from a trial with three transition pathways (pasture, row crop, and intensive vegetable production). Three amendment approaches (manure, compost and cover crops) were used within each transition. Standard soil testing showed use of organic practices increased concentrations of available P and K, Ca, Mg, pH, total organic C and N, soil C:N ratio and labile soil organic matter (SOM) fractions. Changes in SOM fractions were more noticeable than chemical indicators. Temporal data indicated that sampling before and after major tillage operations provides additional information about soil quality that is defined in terms of nutrient supply, habitat provision for soil organisms and prevention of environmental degradation. Soil resource concentrations fluctuated within season and were ranked: pasture>vegetable>row crop systems. Abundances of bacterial feeding nematodes were consistently associated with soil resource condition. Plant parasitic, predators and omnivorous nematodes were related with soil moisture and bulk density in a less consistent pattern. Nematode indicators, based on family taxonomic identification, were evaluated using standard and multi-date sampling during the certification year and found to be closely associated with soil resource indicators. When temporal dynamics were considered, the channel index (CI), plant parasitic index (PPI), enrichment index (EI), and structure index (SI), in that order, explained differences that resulted from three transition pathways. An EI>50 revealed soil nutrient enrichment in the pasture system. A CI>20 suggested the decay pathway was bacterially dominated in the spring following residue incorporation. A decrease in the SI and increase in the PPI after major tillage operations was the result of food web disruption. Overall, this study illustrated improvements in soil status that resulted from organic transition. Nematode-based indices were more sensitive to changes in soil quality than were SOM or chemical measures. Soil testing to optimize biologically-based fertility may require use of biotic indicators and sampling schemes that capture time-dependent dynamics associated with tillage or nutrient additions.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD