Wednesday, November 15, 2006

Influence of Organic Transition Strategy on the Nematode Community Structure and Biologically-Based Fertility.

Carmen M. Ugarte and Michelle M. Wander. Dept. of Natural Resources & Environmental Sciences, Univ. of Illinois at Urbana-Champaign, 1102 S. Goodwin Ave., Urbana, IL 61801

Even though the organic certification standards require that farmers use practices that enhance soil quality, the affect 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 for 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 beginning in the spring of 2006 prior to soil preparation and processed to evaluate the nematode community structure (The Maturity Index-MI), soil and particulate organic matter (SOM and POM) and plant available N measured using the Illinois N test (IL-N).  The MI of preplant soils revealed a nematode community dominated by bacterial and fungal feeding nematodes (families Rhabditidae, Cephalobidae and Aphelenchoididae), which may indicate higher N mineralization.  This was consistent with high levels of plant available N, (IL-N > 235 mg N kg-1 soil), observed in all systems regardless of amendment approach.  Use of aggressive tillage for soil preparation within the low intensity system lowered the MI.  Surprisingly, the POM-C contents of preplant soils from all systems were similar and have already reached ranges found 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. Seasonal trends of the measured variables will be presented.