Underground Herbicides

This article written by Dr. Reynold Bergen, BCRC Science Director, originally appeared in the June 2021 issue of Canadian Cattlemen magazine and is reprinted on the BCRC Blog with permission of the publisher.

When I was a kid, my dad found Russian knapweed in a pasture along an irrigation canal. He explained that it was important to catch this weed quickly, because it can spread very aggressively. Russian knapweed reproduces using seeds as well as by buds growing from its roots (somewhat similar to the sod-forming grasses in last month’s column). But Russian knapweed roots also release a chemical that weakens other plants, like an underground herbicide. This superpower is called “allelopathy”, and helps knapweed establish itself and spread. His explanation was much more interesting than pulling out all the plants later that day.


Western wheatgrass

Weeds aren’t the only plants that can do this. While collecting field data for a project aimed at developing new tame and native varieties and mixtures, researchers at Agriculture and Agri-Food Canada’s Swift Current Research Station and the University of Saskatchewan noticed that there seemed to be fewer weeds in plots that contained western wheatgrass (on its own or in mixtures). This led them to conduct a greenhouse study to learn whether forage plants can also make their own herbicides. These results were published in 2017 (The potential of seven native North American forage species to suppress weeds through allelopathy; Canadian Journal of Plant Science https://cdnsciencepub.com/doi/10.1139/cjps-2016-0354).

What They Did: They seeded five native grasses (western wheatgrass, bluebunch wheatgrass, nodding brome, little bluestem and sideoats grama) and two native legumes (purple and white prairie clover) in individual pots. Each pot contained only one forage species. Continue reading

How Mother Nature Hedges Her Bets

This article written by Dr. Reynold Bergen, BCRC Science Director, originally appeared in the May 2021 issue of Canadian Cattlemen magazine and is reprinted on the BCRC Blog with permission of the publisher.

Pasture plants are generally classified as decreasers, increasers and invaders. Decreaser species are the plants you want to see and your cattle prefer to eat, so they face the most grazing pressure. Increaser plants tend to thrive when the decreaser species are challenged by overgrazing, drought or other sub-optimal conditions. Invaders (weeds) proliferate when increasers and the remaining decreasers are so weakened by overgrazing or environmental extremes that they have a hard time competing for nutrients, water and sunlight. 
cattle grazing on healthy, green pastures
Healthy, productive pastures are dominated by decreasers. The composition of the decreaser community in healthy native rangelands was shaped by thousands of years of natural selection and environmental pressures. In tame pastures, humans take the wheel from Mother Nature as we seek to establish and maintain a stand of tame decreaser species that can be productive and long-lived in our particular soil and climate conditions. In both native and tame pastures, good grazing managers adjust stocking densities, grazing intensities, grazing and rest period length and frequency, etc. based on annual and seasonal variations in growing conditions to maintain pasture health and optimize long-term forage and animal productivity. Continue reading

Carrying or Grazing Capacity

Are you managing a new-to-you pasture and you need to determine how to stock it? Perhaps it has been recently purchased or rented, or you simply don’t trust the information provided on historical stocking rates.

The first principle of pasture management is to balance the available forage supply with livestock demand. Carrying capacity (also known as grazing capacity) is the amount of forage available for grazing animals in a specific pasture or field. A substantial amount of Canada’s rangeland is in some form of public ownership (e.g. grazing leases, forest grazing allotments) and has carrying capacity data available. With privately owned or recently acquired land however, there may not be any information on historical forage production and carrying capacity.

Carrying Capacity is defined as the average number of livestock and/or wildlife that may be sustained on a pasture that fits the management goals. Site characteristics, such as soil, water, plant, and topography of the pasture, can impact carrying capacity. Forage production and availability for grazing can also affect carrying capacity. Source: Society for Range Management, 1998.

Carrying capacity can be calculated using a variety of techniques. All of them depend more or less on trial and error as they are monitored and adjusted over time as the carrying capacity for an individual year varies from the long-term average for the pasture. The effectiveness of each method depends on the kind of grazing land, but a combination of methods is generally required. Continue reading

Exceptional Forages for Marginal Lands

This article written by Dr. Reynold Bergen, BCRC Science Director, originally appeared in the April 2019 issue of Canadian Cattlemen magazine and is reprinted on the BCRC Blog with permission of the publisher.


Side Oats Gramma photo courtesy of Agriculture Agri-Food Canada

Tame forages often outperform native species in head-to-head comparisons under optimal growing conditions. This may not be the case on “marginal land,” with its tougher environments, poorer soil, rougher topography, harsher climates, and precipitation extremes. Beef production is expected to rely more and more on marginal land, at least while returns from cash crops exceed those from cow-calf production.

Beef Cluster research led by Mike Schellenberg (Agriculture and Agri-Food Canada Swift Current), Eric Lamb (University of Saskatchewan) and a team of graduate students has been examining Western Canadian native plants since 2009. Some results from this study were published in 2018 (“Mixtures of native perennial forage species produce higher yields than monocultures in a long-term study”; Canadian Journal of Plant Science 98:633-647).

Continue reading