Exploring the Unique Role of Hairy Vetch in Grazed Green Manure Systems for the Canadian Prairies.

Grazed green manure systems offer some of the benefits of crop-livestock integration without a lengthy forage phase in rotation. Hairy vetch is a productive and versatile annual legume that may be well-suited to grazed green manure systems when spring-seeded in short-season regions like the Canadian prairies. Two grazing experiments were conducted in south-central Manitoba, Canada in 2009-2011 on organically managed land, using sheep. Our objective was to explore hairy vetch grazing systems that take advantage of its extended growth period and regrowth potential in order to optimize forage production and utilization and the nitrogen (N) benefit to subsequent crops. In each experiment, three grazing management strategies were tested, along with haying and soil-incorporation of hairy vetch. Hairy vetch regrowth was negatively affected by delaying grazing until late in the summer and by grazing at high stocking rates. Greatest regrowth potential was achieved in a rotationally grazed treatment in which hairy vetch was grazed very lightly at 3-4 week intervals beginning while it was still vegetative. Spring wheat following the rotationally grazed treatment had significantly (p<0.05) greater total aerial biomass (crop + weeds) and greater aerial biomass N than all other treatments in that experiment, with the same trend observed weakly in wheat yield and grain N and other performance parameters. The cause of this is unclear but could include enhancement of N dynamics due to repeated defoliation by grazing, repeated deposition of excreta, and/or late-season growth of hairy vetch in this treatment. Despite being a common forage crop in many regions, information on grazing management of hairy vetch is scarce. Areas of future research should include hairy vetch palatability and response to trampling and defoliation by grazing in order to optimize its potential for abundant biomass production and N-fixation and an extended and flexible grazing season. The role of livestock in ecological intensification of cropping systems also deserves further research.