Four Years of Autumn Cover Crops on Profit Margins and Crop Yield.

Typically cover crop (CC) research has focused on autumn-planted CC and studying effects in the subsequent season. Although this approach is valid for first time CC users, long-term studies are needed to have meaningful results for growers who consistently plant CCs.  To evaluate the effect of multiple years of cover cropping on the production system, a field split-plot factorial design trial was conducted on a sandy loam, 3.5% OM soil.  Cover crops were planted each autumn after main crop harvest at two experimental sites during 2007-10 and 2008-11, where the main-plot effect was CC type and split-plot was ammonium-nitrate fertilizer rate (0 to 10 vs. ≥100 kg N ha^-1 preplant broadcast incorporated) to the main crop, which varied annually.  Treatments included a no-cover control, oat (Avena sativa L.), cereal rye (Secale cereale L.), oilseed radish (OSR) (Raphanus sativus L. var. oleiferus Metzg Stokes), and mix of OSR and rye (OSR+Rye) drilled at 80, 67, 16, and 9+34 kg ha^-1, respectively. In each of the following springs, the trial area was disked twice and main crops of processing sweet corn, spring wheat, processing tomatoes, field corn were planted with or without N fertilizer and grown according to typical production practices.  At harvest, the lack of a CC by N rate interaction in crop yield, soil N, or plant N content suggests that growers may not need to modify N fertilizer rates based on CC type.  In all site-years, marketable yield and profit margins in the no-cover treatment was lower or not statistically different than all CCs tested, except for rye with spring wheat. For instance, in processing tomatoes profit margins over both years were 1320 $CAD ha^-1 higher with OSR compared to the no-cover.  Delta yield measurements for each cropping season and combined profit margins over the four-year study will be assessed.