Cover Crop Impact on Manure Nitrogen Sequestration and Availability to Corn in Ontario.

Ontario’s Nutrient Management Plan encourages use of cover crops following summer applied manure to sequester nitrogen (N) and increase manure N availability to the following crop.  Twenty-seven on-farm trials were established from 2003-2007 on cereal stubble fields in southern Ontario to evaluate, and quantify, the ability of Oat, Oilseed Radish, Pea, Annual Ryegrass and Red Clover cover crops to sequester N from August applied manure.  On 21 of these sites the impact that cover crops had on corn yield and fertilizer N requirement were also evaluated.  An oat cover crop was included at all sites.  On average, manure increased above ground oat biomass by 50% and N content by 100% (manured oat biomass of 3100 kg/ha with a N content of 79 kg-N/ha). An oat cover crop decreased early November soil mineral N concentration in the surface 30cm by 40%.  Manure N uptake by annual ryegrass, oilseed radish and red clover  cover crops did not differ from those observed with oats when included in the same trials.  Field peas were about half as effective as oats at sequestering manure N.  Oat, oilseed radish and annual ryegrass did not increase N availability to corn planted the next year.  Results from this study suggest that manure N credit adjustments for corn associated with use of cover crops in Ontario’s Nutrient Management Plans may not be justified.