Seeding Rate Effects on Weed Control and Yield For Organic Soybean Production

Abstract

The organic grain 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. Recent soybean population studies show that lower seeding rates for genetically modified organism soybean farmers provide maximum economic return due to high seed technology fees and inexpensive herbicides. Such economic analysis may not be appropriate for organic soybean producers due to the absence of seed technology fees, stronger weed pressures, and price premiums for organic soybean. Soybean seeding rates in North Carolina have traditionally been suggested at approximately 247,000 live seeds/ha, depending on planting conditions. Higher seeding rates may result in a more competitive soybean population and better economic returns for organic soybean producers. Experiments were conducted in 2006 and 2007 to investigate seeding rates of 185,000, 309,000, 432,000, and 556,000 live seeds/ha. All rates were planted on 76-cm row spacing in organic and conventional weed management systems. Increased soybean seeding rates reduced weed ratings at three of the five sites. Increased soybean seeding rates also resulted in higher yield at three of the four sites. Maximum economic returns for organic treatments were achieved with the highest seeding rate in all sites. Results suggest that seeding rates as high as 556,000 live seeds/ha may provide organic soybean producers with better weed control, higher yield, and increased profits.