Influence of organic transition strategies on the nematode community structure and biologically based fertility

Even though the organic certification standards require that farmers use practices that enhance soil quality, the effect of various transition strategies on soils is not well known.  The goal of this project is to understand the relationship between transition strategies, soil quality attributes, and soil biological activity. We collected soil samples from a trial comparing three strategies to transition.  These included a ley crop (low intensity), row crop (intermediate intensity), and intensive horticultural (high intensity) systems. Within each strategy, three amendment approaches (fresh manure, compost and cover crops) were used. Soil samples were collected in four dates during the 2006 growing season and processed to evaluate the nematode community structure (The Enrichment Index-EI and Structure Index-SI), particulate organic matter (POM), and potentially mineralizable N (PMN).  The EI (EI = 65-90%) of preplant soils revealed a nematode community dominated by members of Rhabditidae, Diploscapteridae, Aphelenchoididae and Aphelenchidae, which may indicate higher N mineralization.  This was consistent with high levels of PMN > 22 mg N kg^-1 soil.  Surprisingly, the POM-C contents of preplant soils from all systems were similar to those in long-term established organic farming trials (1.8-2.7 g C kg^-1 soil).  All three transition strategies successfully built SOM and N concentrations during the transition period and thus can supply adequate fertility to N demanding crops. In addition, nematode community indices were significant predictors of changes in soil quality as induced by different intensities of management.