Productivity, Pest Management, and Soil Quality in Organic Farming Systems.

Organic growers use livestock-based rotations, green manures and compost applications to maintain soil quality and crop productivity.  To evaluate the long-term consequences of organic farming systems practices, the West Virginia University Organic Research Farm project was initiated in 1999, and became certified in 2003.  Farming systems trials compare yields, soil quality, and pest populations in replicated plots.  A low input system for market garden vegetable production maintains soil quality solely with green manures and cover crops in the rotation, while a high input system supplements these crops with annual applications of dairy manure compost.  Low and high input field crop systems were evaluated in a factorial design with versus without a pasture/livestock component in the rotation.   Yields were usually higher in high input plots, however, adding livestock/pasture to the rotation generally had little effect on crop yields.  Soil quality parameters measured included macronutrient levels, organic matter content, and earthworm population density. These generally showed few differences among treatments during the first 3-4 years of the experiment.  Soil organic matter content increased over time in both low and high input plots, however, soil fertility levels and organic matter content were greater in high input than low input plots after 2003.  Earthworm population density and biomass were greater in high input plots, however, population age structure shifted.  A majority of specimens were adults at the start of the experiment, but the proportion of juveniles increased steadily (over 90 % of the population by 2008).  Insect pest populations showed few differences among compost treatments, whereas weed communities and soil-borne diseases differed significantly.  Seed rot and damping off diseases were persistent problems, especially in peas, spinach, and soybean.  We conclude that off-farm sources of compost provided significant benefits, and green manure/livestock-only systems did not adequately maintain soil fertility or crop yields.