Early-seeded annuals preserve perennial pastures

Swath grazing is typically used as a way to provide high-quality forage for cattle on pasture through the fall and early-winter months. A “rested grazing project,” in its third year at Agriculture and Agri-Food Canada’s Brandon Research Centre, is showing that moving swath grazing to the late summer has the potential to increase grazing days by about 50 per cent compared with fall swath grazing in the same system.

Preliminary results suggest that the increase has a lot to do with taking advantage of the yield potential of annuals by planting them as early as possible on the spring moisture in May versus postponing seeding into June, which is the normal practice for fall swath grazing, explains Dr. Shannon Scott.

The boost in carrying capacity comes at no additional cost because input costs were identical for the May-seeded and June-seeded annuals, she adds. The timing of planting and swath grazing were the only parameters they changed.

The research team set up the study to look at whether or not resting perennial pastures during the critical late-season period from the beginning of August until the first killing frost would improve perennial pasture productivity and persistence of alfalfa, if present. The general recommendation is to avoid grazing or haying alfalfa during this period so that it has time to build energy reserves in the root system before going into dormancy for the winter. Grazing perennial forages after dormancy should significantly reduce the long-term negative impact on forage production and persistence that tend to occur when they have been grazed during the latter part of the growing season.

Three years into the study, Scott says there appears to be more alfalfa on the rested perennial pasture than in the pasture that has been rotationally grazed as usual throughout the entire summer, though she won’t be able to officially comment on that angle until the data are analysed after the study wraps up next year.

The trial

The perennial pastures in the trail are well-established paddocks of straight meadow brome or mixed grasses and alfalfa.

The annual forages alternate from oats one year, to barley the next. The early-seeded annual is planted as early as possible in May. The late-seeded annual is sown in mid-June. Each is swathed when it reaches the soft dough stage.

Four groups of cow-calf pairs rotate through their assigned perennial pastures (either grass only or grass-alfalfa) and are moved every 10 to 12 days from early June until the end of July. The cows in each group will continue together for the four years of the study.

The perennial pastures are divided in half at the beginning of August. One part is rested and the other is grazed following a normal rotation. The pairs from the pastures to be rested move onto the swathed early-seeded annual for grazing. Cross fencing is used to portion out fresh swath each day. This phase ends when either the swaths or the non-rested perennial pasture run out.

That’s when the calves are weaned. For the purpose of the trial, the cows are moved to pens or other pastures until the first killing frost.

The final phase of the grazing season begins when the cows that had been swath grazing the early-seeded annuals move onto the stockpiled, rested perennial pasture. They stay there until it has been grazed to the same extent as the non-rested pasture. The groups that had been grazing the perennial pastures as usual throughout the summer go to the late-seeded annuals for swath grazing until they clean it up.

The cows and calves are weighed and the cows are scored for body condition at the beginning and end of each phase of the trial. Clippings are taken at predetermined places in each paddock throughout the trial to monitor perennial pasture productivity, quality and plant composition. Feed tests are done on samples taken from the swaths and any regrowth as grazing progresses. The mass of the residual material is measured to estimate intake.

Observations

The first year of the trial was a dry year. The early-seeded oats provided 360 animal unit days of grazing per hectare (AUD/ha) compared with the late-seeded oats, which provided 152 AUD/ha.

Barley was the annual crop in year two. It provided 520 AUD/ha when

sown in May versus 315 AUD/ha when seeding was delayed until mid-June.

Both years, the stockpiled, rested perennial pastures provided more AUD/ha when grazed after dormancy than the perennial pastures that were grazed all summer long.

When the numbers were added up, sowing the annual crops early and swath grazing them during the late summer increased the carrying capacity of the grazing system by approximately 50 per cent compared with delaying the seeding of the annuals for fall swath grazing and grazing the perennial pasture all summer long. A bonus was that summer swath grazing left lots of time for fall herbicide applications.

This study, funded by the Beef Cattle Research Council and Manitoba’s Agriculture Research and Development Initiative, is being carried out in co-operation with Dr. Martin Entz and Mr. Simon Neufeld of the University of Manitoba.

Contact Shannon Scott, 204-578-3605.

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