Smooth bromegrass is a cool-season introduced grass with an advanced root system that tolerates temperature extremes and drought exceptionally well. This sod-forming perennial grass spreads rapidly through seeds and rhizomes causing pastures and rangeland in Central South Dakota to be increasingly dominated by this grass year after year.
As pastures become dominated by smooth bromegrass, plant diversity begins to suffer as less native grass species are able to compete and are squeezed out of the pasture. As pasture diversity declines, the ability to effectively utilize the forage available through grazing becomes more challenging. Smooth bromegrass has a much shorter effective grazing window compared to pastures dominated by native cool and warm-season grasses.
Smooth bromegrass grows best when temperatures are between 60 and 75 degrees Fahrenheit. Growth begins in mid to late April followed by a rapid growth phase in early to mid-May. During the summer, growth slows considerably and the plant will go dormant through July and August. Fall regrowth typically occurs in early September through mid-October as sunlight intensity decreases. During the rapid growth phase in early to mid-May, the amount of forage produced quickly outpaces animal intake leading to poor forage utilization.
Figure 2. Forage distribution of smooth bromegrass through the growing season. Courtesy of Undersander et al. (2002).
How can a ranch manager address this challenge and achieve effective forage utilization? The following guidelines for spring, summer, and fall grazing periods may assist ranch managers to develop a grazing strategy for pastures where smooth bromegrass dominate.
- All-Season: If the smooth bromegrass pasture is grazed the entire season, moderate stocking rates must be used to ensure enough forage is available during the summer months when forage production decreases. Initial turnout in spring should occur when forage height reaches 12-14 inches. Smooth bromegrass should not be grazed to a stubble height below 4 to 6 inches.
- Spring, Summer, Fall Rotation: If another pasture with native warm-season grasses is available on the ranch, an alternative strategy is to increase stocking rates on smooth bromegrass during spring, move to the native warm-season pasture in summer, then return to the smooth bromegrass in the fall with moderate stocking rates.
- Rotational Grazing: Rotational grazing systems can help better utilize smooth bromegrass during the rapid growth phase. However, if no rotational grazing system is present on the ranch, an in depth cost/benefit analysis must be completed before large amounts of capital are invested in fence and water improvements. Starting slowly and carefully with one or two cross fences will allow the start of a simple rotational grazing system with minimal cost.
- Summer & Fall: Smooth bromegrass quality is lower during the summer months, which makes mineral supplementation necessary during this time period. At least 8 to 10 inches of regrowth should be available in fall grazing pastures. Grazing animals should be removed from fall grazing pastures when stubble height reaches 4 to 6 inches.
The bottom line
In spite of the fact that smooth bromegrass has invaded several native grass pastures and rangeland in Central South Dakota, with some effective grazing management strategies, ranch managers can turn smooth bromegrass into a valuable asset to the ranch.