Effects of transition to organic management on soil carbon and nitrogen pools and microbial, nematode and microarthropod communities in a field crop transition experiment

A Field Crop Transition Experiment was established at the Ohio Agriculture Research and Development Center in Wooster in March 2000 to build understanding of ecological changes in land that is transitioned from conventional to organic production.  The experiment compares conventional low-till corn-soybean and certified organic corn-soybean-oats-hay farming systems.  Soil aggregation, bulk density and compaction did not differ between the two systems, suggesting that high organic matter additions are buffering negative impacts of tillage in the organic system.  pH, total N, P, K Ca, Mg, and Cu, became significantly higher in the organic than the conventional plots while Al was significantly lower.  Ammonia and nitrate N concentrations were higher in the conventional than in the organic system, especially in conventional corn plots.  Total soil organic matter, soil carbon and particulate organic matter were slightly higher in the organic than conventional system by Fall 2001. Carbohydrates dominated both systems in spring 2002 and there was little difference in carbon structures between the two systems at that point in the transition.  Microbial biomass-N was higher in the organic than the conventional system especially in the corn and hay parts of the rotation.  However, DNA evaluations of the soil bacterial and fungal communities indicated no difference in species composition in 2002 and 2003.  Major changes in nematode community composition were observed within the first six months of transition, with a shift in dominance from plant parasitic to free-living nematodes.  Although variability was high Mesostigmatid mites including Uropodina increased dramatically in the organic treatments.