Intercropping Clover and Winter Wheat: Effects On Grain Yield, Soil Nitrogen Content, and Weed Pressure in an Organic Wheat-Corn-Soybean Rotation.

Legume cover crops in organic production systems add nitrogen and organic matter to the soil, and have the potential to suppress weeds. Intercropping legume cover crops with small grains extends the legume growing season, but might affect grain yield and grain protein content. This study investigated the effects clover-wheat intercrops have on wheat grain yield and grain protein, weed pressure and soil nitrogen levels in an organic wheat-corn-soybean rotation. Treatments consisted of intercropping red clover (Trifolium pretense) with wheat (RC), intercropping white clover (Trifolium repens) with wheat (WC), and sole cropping wheat (NC). Clover was sown into a winter wheat stand in March 2011. Whole plant biomass samples for wheat, clover, and weeds were taken in July at wheat harvest and in October before clover plowdown. Wheat grain yield was obtained at harvest using combine weight. Grain protein content was obtained with near-infrared analysis. Soil was sampled after clover planting in April, after wheat harvest in July and before clover plowdown in October. In 2011, wheat yielded 3.81 Mg ha^-1 in the WC treatment, 3.75 Mg ha^-1 in the RC treatment and 3.68 Mg ha^-1 in the NC treatment, however, the differences were not significant. Grain protein ranged between 11.2 and 12.1%, and did not differ significantly between treatments. At time of harvest, WC had the highest weed dry weight. In the fall, nitrate levels were lowest in RC. In 2011, rainfall was sufficient for an excellent stand development of the red clover. White clover stand density was poor. Overwintered red clover formed a dense, virtually weed free stand in the spring of 2012. This type of legume-cereal intercropping could be beneficial for Eastern Nebraska growers wanting to plant a non-soybean legume cover crop with good weed suppressing potential prior to corn planting.