Soil Amendment Effects On Pesticide-Free Flaxseed Production in Central Iowa.

Demand for flaxseed (Linum usitatissimum) oil has increased recently due to discovered health benefits and an emerging market for organic flaxseed. Researchers and farmers are now challenged to determine the best methods to grow flax in organic systems in the Midwest. Organic growers are particularly concerned about adequate fertility and weed management when adding flax to their crop rotations. Our experiment was conducted in central Iowa in 2007 and 2008, on land without organic certification, but also in the absence of any synthetic pest control. The objective of the study was to evaluate flaxseed yield response to different nitrogen fertility sources (composted swine manure, liquid swine manure, urea) and rates (0, 30, 60, 90 lb N/acre) when the crop was grown after soybean or corn. To determine the influence of weed competition on flaxseed yield, half of each plot was hand-weeded to establish near weed-free conditions. Seed quality factors that can ultimately determine market value such as oil content and fatty acid profile were also measured. Results from the two-year study indicate yield responses to soil amendments varied depending on year, previous crop, and weed presence. In 2007, the highest flaxseed yields were observed following a soybean crop and in the absence of weed competition. Seed yield did not respond to soil amendment in 2008 likely due to late planting as a result of wet field conditions. Weed competition reduced seed yields to 32-96% of those measured in near weed-free conditions regardless of year, previous crop, fertility source, and rate. In most cases, seed quality factors responded negatively to increased rates of fertility.