Cultural Strategies for Optimizing Agronomic Performance of Reduced Tillage Organic Soybean Production.

Weed management is the primary limitation to successful cover crop-based, no-tillage, organic soybean production. When traditional control tactics are not used (tillage and herbicides), it is critical to identify tactics that when combined, synergize weed suppression while optimizing crop performance. In this study, cereal rye biomass and soybean plant density were varied to enhance weed suppression.  Five levels of rye residue representing 0, 0.5, 1, 1.5, and 2 times the ambient level (~6,500 kg ha^-1) were established in a complete split-block design with five soybean densities ranging from 0 to 741,000 seeds ha^-1. Synergistic effects were observed between the seeding rate and mulch rate treatments, resulting in delayed weed emergence, and reduced weed emergence and biomass.  The synergistic effects can largely be explained by reduction in light transmittance with increasing soybean population and higher mulch rate. While mulches can reduce the competitiveness of weeds, high rates of residue can also impact soybean emergence (>40%). Since the cost of soybean seed can limit the range of seeding rates growers will plant at, future work should focus on identifying other complimentary weed management tactics that minimize weed competition and enhance soybean performance.