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To rejuvenate a pasture focus on legumes and weeds

High-intensity/low-frequency grazing was the most effective system for the grasses to remain competitive

Calf eating musk thistle

Graeme Finn and his wife Heather rent 3,200 acres of pasture on long-term lease to graze 1,000 yearlings and their beef cow herd year round near Madden, Alta.

They rely on intensive rotational grazing of high-legume and annual crop pastures so you can understand why each pasture was assessed for potential productivity before it was rented.

In the past, most of those pastures required major rejuvenation primarily to get rid of the weeds, particularly thistles.

“I mainly sod seed my pastures,” explains Graeme. “My goal is to start off with a clean seedbed and for weed control and existing vegetation control I use a fall and/or spring burn-off with glyphosate. If chemicals will help me, I will use them,” says Graeme. “My planting depth is critical and I aim for seeding at one-half inch in depth.

“I seed a very heavy mixture of different legumes mainly alfalfa, vetch and sainfoin with the grass. The more legumes the better… like up to 60 per cent. The vetch and sainfoin help to prevent bloat. When I am sod seeding, I like to use 10 pounds per acre of a grass blend of AC Knowles hybrid bromegrass, smooth leaf tall fescue and orchardgrass. The legume mixture of Splendor 4 alfalfa, Veldt milk vetch and sainfoin is seeded at five pounds an acre. After a couple of years there is more vetch and sainfoin repopulating in the stand. I find that a mixture of grasses and legumes gives me the best milk production and weight gains for my grazing cattle. Do not be afraid of using legumes; with grazing management they can be the best thing for your pastures.

“I still have lots of alfalfa in my pastures after 10 years. I don’t graze my pastures like a hay mower. I have lots of plant height left at the end of the grazing period to be used as solar panels for future plant growth.

“I firmly believe that in my area it is essential to not graze the newly seeded pasture for the next 12 months. This is critical and I have found that this long initial rest period will extend the life of my pastures for up to 10 to 12 years. Depending on the situation, I will graze the new stand in the late fall or stockpile graze it lightly in the winter. I have a grazing plan where the cattle will graze while the newly seeded pasture is locked out for the year’s rest period.”

Sod seeding using a direct-seed drill at six- to seven-inch spacings costs about $62 per acre for chemical plus seed. If he has to break the old pasture and cultivate before seeding, his costs climb closer to $150 plus seed.

“High-quality forage has low fibre, high protein and tastes good. The sugars in the plant are the immediate product of photosynthesis which hasn’t yet been incorporated into the plant structure. The less mature the plant, the greater the proportion of total dry weight of the plant that is made up of cell-soluble material. This is good grazing. In immature plants, a much higher amount of cellulose may be digested, while in mature grasses less than 25 per cent may be digested,” he says.

“Overgrazing, is the most harmful practice to any pasture. You always need to leave sufficient grass to be a solar panel. Overgrazing will also shorten the life of your pastures and increase your costs.

“I use rotational grazing as it is both beneficial to the cattle and the pasture land. Electric fencing is one tool that I use to make grazing easier. I always provide fresh water and I supply this through plastic pipelines and strategic placement of watering points. I also stockpile forage for fall-winter grazing and this is very important to my year-round grazing program for my beef cows. I find that when cows graze late in the fall and early winter, when the legumes have seed heads, they will spread these seeds around the field.

“By having a good mix of grasses and legumes in the pasture stand I can improve the soil fertility as well as the production of the livestock. By having multi species in a pasture stand I can have good productive grazing from spring to fall.

“I have also found that good plant diversity suppresses the spread of weeds, harmful insects, diseases. It also broadens the nutritional opportunities of grazing livestock.”

By inter-layering legumes throughout the grass canopy Graeme creates a more efficient pasture than is possible with just grass or legumes alone. This also lessens the threat of bloat, as the cattle can graze a mouthful of grass followed by a mouthful of alfalfa or other legumes.

He also uses annual forages to control weeds with heavy seeding rates of forage rape and annual ryegrass. These crops grow so thick they cover the soil and smother encroaching weeds. There is basically no space for the weeds to grow.

Overgrazing is the most common way weeds take over a pasture. In travelling across central Alberta and Saskatchewan last fall, I was hard pressed to find any pasture that had not been severely overgrazed, some almost to the ground. Only Kentucky bluegrass and creeping red fescue remained, two grasses not noted for high forage production. As a result, Canada thistle and other weeds dominated the landscape.

Canada thistle is considered by livestock producers to be the most problematic pasture weed on the Canadian prairie. Its roots spread one to two metres a year and can extend six metres. Root pieces as small as half a centimetre long can produce viable plants. Canada thistle is a very aggressive weed and takes light, moisture and nutrients from surrounding forages.

Dr. Ed Bork at the University of Alberta and his graduate students studied how Canada thistle responds to clipping of the surrounding plants. “We found that continuous clipping down to a height of approximately one inch every 14 days simulated maximum stress on forages… and resulted in the lowest grass production on fertilized and unfertilized pastures sites.

“High-intensity/low-frequency sites clipped to approximately one inch every six weeks provided the second-highest grass production, showing once again that a rest period is critical to forage regrowth. Deferred grazing sites were clipped once at the end of the growing season (mid-August) following unimpeded growth throughout the summer.

“The highest forage biomass came from fertilized and unfertilized plots in the deferred grazing sites. Thistle growth was highest in the continuous grazing system, followed by low-intensity/high-frequency, high-intensity/low-frequency and deferred grazing systems, in that order.”

In another study, Bork and his team evaluated high-intensity/low-frequency, low intensity/high-frequency and continuous grazed pastures.

Thistle coverage was in excess of 32 stems per square metre on continuously grazed pastures. Thistle counts dropped somewhat to 24 stems per square metre by the end of the third year on low-intensity/high-frequency grazed pastures and managed to achieve 40 per cent forage utilization with two weeks rest between grazing periods.

Cattle in the high-intensity/low-frequency pasture were allowed to graze 70 to 80 per cent of the available forage over five days, and then the pasture was rested for six weeks. This combination was hardest on the thistles at fewer than two thistle plants per square metre after three years.

High-intensity/low-frequency was the most effective system because the recovery period was sufficient for the grasses to remain competitive so the cattle ate the thistles rather than selectively graze around them. That in turn kept most of the thistles in the early growth stage or rosette stage, when they are at their most palatable and nutritious, averaging 18.6 per cent crude protein and 83 per cent total digestible nutrients.

The cattle consumed some thistles in the low-intensity/high-frequency pasture, but not enough to provide effective control.

“Cattle didn’t touch the thistles in the continuous grazing system, letting them advance to the late-flower state,” says Bork. The weeds had more stems, were pricklier and harder for animals to eat and digest than young thistles.

“A year after producers had reverted back to continuous grazing, the thistles had not recovered on the high-intensity/low-frequency pastures, and a big increase in total forage productivity was still evident. The greatest thistle control coincided with the grazing system that gave the best forage production and best utilization of thistle.”

Eat them down

It is important to put these cattle immediately in a thistle-infested pasture so they don’t lose their taste for them. Calves grazing alongside their mothers will also learn to eat thistles and this behaviour will be remembered throughout their grazing life.

Graeme has used goats to graze buck brush on his pastures. The key, he says, is to keep the goats or cows in a concentrated area with electric fencing to get them to graze a specific weed right down to the ground. Later in the day they must be let out for water.

Clark Brenzil, provincial weed specialist with Saskatchewan Agriculture sums it up very well. Prevention is the key and cheapest way to control weeds on pasture and rangelands. Once the weeds are introduced, you need to find them and eradicate them right away. You want no survivors. Some weeds have the potential to spread a million seeds per plant across your pasture and rangelands.

Detailed information on pasture rejuvenation and weed control on pastures can be found at Look for the invasive species and pasture rejuvenation section.

Duane McCartney is a retired forage beef systems research scientist in Lacombe, Alta.

About the author


Duane McCartney is a retired forage-beef systems research scientist at Lacombe, Alta.



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