Effects of Long-Term Management on Soil Organic Matter and Weed Competition in Organic Soybean.

Ecological weed management relies on cultural practices to reduce weed populations and weed competition with crops. This approach can buffer cropping systems against yield losses from weeds, and potentially increase profitability in both organic and non-organic cropping systems. Competitive interactions between weeds and crops can be manipulated by altering soil nutrient pools and the quantity and quality of organic matter. Long-term management legacies can influence these soil properties, and thus can influence weed-crop competition. We quantified weed-crop competition in a nested component experiment within the Cornell Organic Grain Cropping Systems Experiment in Aurora, NY. This long-term experiment was started in 2005 and compared four organic cropping systems that varied in fertility inputs, weed management, and tillage. Competition intensity between weed and soybean in each cropping system was quantified across an experimentally manipulated weed intensity gradient. Soil organic matter quantity, quality, and nutrient levels were also detailed in each system. Preliminary results indicate differences in weed-crop competition between cropping systems, which could be explained by differences in management legacy and soil properties.