With grain and oilseed planting close to finished, producers with livestock may be looking at seeding some fields for swath grazing. So when is the best time to seed grazing crops?
“Several studies across Alberta and Saskatchewan tend to tell the same story,” said Mark Johns, forage specialist with Alberta Agriculture at Stettler.
“The later swath grazing crops are seeded, the less yield there will be. The late June to early July plantings can miss several weeks of the best growing conditions, and can result in yields that are about two-thirds of a May-seeded crop. That translates to a loss of approximately one ton per acre.”
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Many barley varieties need 1,250 growing degree days, or GDD, to reach the soft dough stage. Based on the average temperature values for the Red Deer area, 1,250 GDD is roughly the heat accumulation between the end of June and the end of September. Late seeding runs the risk of a hard frost before the crop is at the soft dough stage.
“If the planting date is backed up to the middle of June, the 1,250 GGD mark will be approached by the middle of September. While producers may consider seeding even earlier, they must remember that an early-seeded and early-harvested crop can have more weathering and mould growth,” Johns said.
“This is true especially if August is cold and wet, as it was last year. If the crop is cut during the first few weeks of September, the cooler temperatures reduce the amount of quality loss and mould growth in the swath, particularly those mould varieties that can be harmful to cows.”
Another penalty for seeding too late can be a higher accumulation of nitrates in the crop, particularly with July-seeded oats. This was common in 2005.
While the base levels for nitrate toxicity are likely too conservative when applied to swath grazing, there are so many variables that test results must be taken seriously until they have been discussed with a veterinarian or nutritionist.
“Less likely, but still a factor to consider, is the effect that light frosts and near freezing temperatures can have on the mineral content of plant tissue,” added Johns.
“Cold stress on immature plants, followed by a few days of decent growing weather, can cause plant potassium levels to increase, while sodium, calcium and magnesium tend to drop. From a cow’s dietary point of view, this can be less than ideal. In extreme cases it may result in winter tetany.”
So when seeding a swath grazing crop, plant early enough to take advantage of spring moisture, but late enough to be swathing the crop just before the killing frosts of fall. To have the best combination of yield and quality, barley and triticale should be swathed in the early dough stage, while oats must be cut in the milk stage.
The Western Forage-Beef Group at Lacombe, Alta., has been actively researching the best seeding windows for swath grazing crops. While it is too early to provide specific dates, there are some guidelines that can be followed.
Forage and pasture agronomist Arvid Aasen said for central Alberta producers, “in most cases, barley could be seeded by the middle of June. Triticale, oats and oat-barley mixtures would be OK seeded as early as the first week of June.”
