GREEN MACHINES Grazing expert says producers need to gauge ‘range readiness’ and carefully monitor the amount of defoliation
Good pastures start with a good understanding of how plants grow.
Attendees at the recent Original Grazing School for Women were given some key pointers by Edward Bork, who is director of the Rangeland Research Institute at the University of Alberta and also operates a grain and beef operation with his family near Chipman.
Grasses can be grazed because they grow from the base — not the tip of plant — and recover quickly because of their large root mass — which account for up to 85 per cent of the plant’s mass and typically extend two to four feet deep.
But producers need to understand concepts such as “range readiness,” said Bork.
“At the minimum, we should wait until the plants reach the rapid growth phase,” said Bork, noting that defoliation impacts both shoots and roots.
“If we remove a lot of the leaf area, the plant has to sacrifice some of those roots, because it doesn’t have enough energy to keep all of those roots alive.”
Plant growth is slow at the start of the spring, and slows again as plants reach maturity. The rapid growth phase occurs in between and effective grazing keeps grasses in that state much longer.
“You want to take off enough biomass to keep them in a vegetative state and actively growing,” Bork said.
Grazing too early comprises grasses and prevents them from achieving maximum production. And growth rates vary among species — crested wheatgrass, meadow brome and smooth brome are fast growing while some of the native grasses, such as rough fescue, take much longer to build leaf area and root mass. Native grasses can be grazed to about the 50-per-cent level while tame pastures, such as brome, can be grazed to around 60 per cent. Bush pasture should only be grazed around 30 per cent.
“The objective is to remove enough green leaf area so plants are still healthy and have the ability to recover,” said Bork. “This is a balancing act.” Moderate stocking rates can help maintain proper grazing. “If you overgraze one year, you’ll pay a significant price the next year and the year after that,” Bork said.
Plants that grow from the top, such as aster and alfalfa, present an additional challenge and require more careful management, he said.
Producers also need to keep in mind that cows are picky eaters, and have a taste for fresh shoots and certain species.
“This selectivity complicates things a lot, but it also helps us,” said Bork. “Selective grazing is a good thing because it allows animals to pick out the highest nutritional items and put that into their diet.”
Still, it’s important to ensure relatively even grazing or else some species will decline while less-favoured ones go to seed and spread. Properly managed rotational grazing prevents this from happening, said Bork.
“It increases the control of where the animals graze, what they graze, how long they graze for, and the rest period in between,” said Bork.
Rotational grazing can also be used to combat unwanted plants such as Canada thistle or leafy spurge — although those species are better controlled by goats and sheep rather than cattle, which find them very unpalatable and may lose condition if forced to graze such weeds.