The effects of sheep grazing for Pisum sativum or Melilotus officinalis cover crop termination
Westbrook, Jasmine Katherine.
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Integration of sheep grazing into crop rotation systems has been proposed as an alternative to conventional cover crop management techniques. However, the effectiveness of this approach and its impact on subsequent crops has not been evaluated in Montana. This study assessed the use of sheep (Ovis aries) grazing to terminate field pea (Pisum sativum) and yellow sweetclover (Melilotus officinalis) cover crops used in rotation with winter wheat. Cover crops were terminated using either rotational or continuous grazing treatments and their effects on cover crop termination, sheep live weight gains, and winter wheat emergence and yield were quantified. Sheep grazing for cover crop termination was also compared to chemical termination and mechanical tillage. In 2013, yearlings grazed the winter pea cover crop for 32 days. Sheep grazing was an effective termination method (77% dead, 1% live, 22% bare ground). Average daily gains (ADGs) did not differ between grazing treatments with sheep exhibiting ADGs of 0.181 kg day -1 for rotational (230 sheep ha -1)and 0.154 kg day -1 for continuous (57 sheep ha -1) treatments (P = 0.12). Winter wheat seedling emergence post grazing was higher under the continuous grazing treatment (P = 0.017), however winter wheat yield did not differ between treatments (P = 0.91). Results indicated grazing was a viable method for terminating a pea cover crop. In 2014, yearlings grazed the sweetclover cover crop for 40 days. Sheep grazing at stocking densities of 44 and 178 sheep ha -1 did not provide effective termination (40% dead, 34% live, 9% bare groundcover). Average daily gains did not differ between grazing treatments with sheep exhibiting ADGs of 0.177 kg day -1 for rotational and 0.172 kg day -1 for continuous treatments (p = 0.79). Termination was achieved using a second group of sheep at stocking densities of 119 and 477 sheep ha -1. Winter wheat seedling emergence did not differ between grazing treatments (p = 0.95). Winter wheat yield was lower in grazed plots than tilled and chemically terminated plots. Grazing has the potential for effective cover crop termination comparable to tillage or herbicide, but results may vary with cover crop species.