The Good, the Bad, the Ugly, and the Unexpected of Integrating Cultural and Mechanical Tactics for Organic Soybean Weed Management.

The organic grains sector is one of the fastest growing sectors of the organic market, but farmers in the mid-Atlantic cannot meet the organic grain demand, including the demand for organic soybean. Weed management is cited by farmers as the largest challenge to organic soybean production. Various non herbicidal weed control practices such as increased soybean seeding rate, increased soybean seed size, mechanical weed control, and roll killed rye cover crops have been shown to effectively reduce weed pressures. However, the effectiveness and interaction of these practices in an integrated system are not well understood. Research was conducted at Kinston, NC in 2010 to investigate the effect of the use of larger soybean seed (largest 15%, largest 50%, and unsorted seed) and increased soybean seeding rates (247,000, 494,000, and 741,000 seed/ha) in a traditional organic secondary tillage system, soybean grown in a no-till roll killed rye system, and soybean treated with conventional herbicides. Various soybean canopy measurements were taken throughout the season as well as weed density measurements for dominant weed species. At higher seeding rates, rotary hoe damage to soybean increased in the mechanically tilled system. Early vigor advantages were seen with increased seed size but such advantages dissipated as the season progressed. An increased seeding rate resulted in a taller, wider, and more vigorous soybean canopy. Unexpected leaf morphology effects were also noted with decreased petiole and leaflet lengths in the rolled rye system compared to the organic tillage and conventional herbicide system.