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Smooth Bromegrass

Smooth bromegrass (Bromus inermis L.) is a leafy, sod-forming perennial grass that is best suited for hay or early spring pasture. It is deep-rooted and spreads by underground rhizomes.

It matures somewhat later in the spring than orchardgrass and makes less summer growth than orchardgrass. Forage quality of smooth bromegrass compares well with other cool-season grasses, being affected primarily by stage of maturity.

Smooth bromegrass is the most widely used cool-season grass in North America. It is grown extensively in Canada and the north-central United States. Smooth bromegrass survives periods of drought and extremes in temperature (Table 1). It can be grown on a variety of soil types, but grows best on well-drained silt-loam or clay-loam soils. It is fairly tolerant of alkalinity and somewhat tolerant of salinity and acidity but will perform best at a soil pH between 6.0 and 7.0.

Table 1. Characteristics of perennial cool-season grasses in Pennsylvania.
Grass Seedling vigora Tolerance to soil limitations Persistance Tolerance to frequent harvest Relative maturityc
Droughty Wet Low pHb
a L = low, M = moderate, H = high
b pH below 6.0
c Maturity characteristic refers to relative time of seed head appearance in the spring. This will depend not only on the species but also on the variety.
Kentucky bluegrass M L M M H H Early
Orchardgrass H M M M M H Early-medium
Perennial ryegrass H L M M L H Early-medium
Reed canarygrass L H H H H H Medium-late
Smooth bromegrass H H M M H L Medium-late
Tall fescue H M M H M H Medium-late
Timothy M L L M H L Late

Adapted Varieties

Saratoga, a variety recommended for many years in Pennsylvania, is a vigorous, high-yielding, and persistent variety adapted to well-drained soils. Baylor, like Saratoga, is a high-yielding and persistent variety in Pennsylvania. These varieties start growing earlier in the spring and stay green longer than “common” bromegrass. Common bromegrass is not a variety but a bromegrass of uncertain genetic makeup.

Establishment

A moist, firm seedbed is required for smooth bromegrass or bromegrass-legume mixtures. Most often planted in spring, smooth bromegrass may also be planted in late summer, when weather conditions usually are more favorable.

Seed may be either drilled or broadcast. Drilling is preferred because it provides a more uniform depth of planting. Plant seed ¼-to ½-inch deep. Long, narrow bromegrass seeds, however, often bridge in conventional seed drills and make planting difficult. Alternate seeding methods may help avoid this problem: (1) mixing bromegrass seed with a small amount of super phosphate and sowing through the fertilizer attachment of the grain drill, or (2) mixing bromegrass with a small amount of oats and sowing through the small grain attachment of your grain drill (only for spring seeding).

Most hopper-type fertilizer spreaders can be calibrated to broadcast smooth bromegrass seed. If seed is broadcast, however, be sure to cover the seed. This can be done by light disking or by following with a drag or harrow.

Smooth bromegrass seeding rate varies with seedbed condition, method of seeding, and quality of seed. Generally, when seeding bromegrass alone, rates of 12–16 lb per acre are sufficient. When seeding in mixtures with a legume, seeding rates of 6–8 lb per acre of bromegrass are recommended (Table 2).

Table 2. Seeding rates for smooth bromegrass and a single legume in mixture.
Species lb/A
Smooth bromegrass 6–8
With any one of these legumes
Alfalfa 8–10
Birdsfoot trefoil 6–8
Red clover 6–8
White clover 2–4

Harvest Management

Growth stage is the most important factor in smooth bromegrass harvest management. Bromegrass is somewhat tolerant of light grazing during the tillering stage of growth. During this initial flush of growth, the growing point is below the ground. Later, when shoots begin to elongate (jointing stage of growth), the growing point may be destroyed by mowing or close grazing.

If the growing point is destroyed at early jointing, regrowth will be slow because new growth will have to come from basal buds not yet developed. When seed heads emerge, it is time to clip pastures or to harvest the forage for hay or silage. This will assure quality forage and quick regrowth of the new crop. Timely harvest of the spring crop resulted in a 33 percent increase in total season yield over harvesting too early. Smooth bromegrass persistence and yield are adversely affected by early harvesting of the spring growth (Table 3). However, delaying the spring harvest beyond early bloom will result in large reductions in forage digestibility and protein content (Table 4).

Table 3. Yield and persistence of perennial cool-season grasses when the first harvest was taken at different stages of grass development and fertilized at two rates of N, averaged over three production years.
Stage at first harvest Na Dry matter yield Persistance after three years
OGb RCb SBb Timb OG RC SB Tim
a High N treatments received 200 to 250 lb N per acre per year, low N treatment received 100 to 125 lb N per acre per year.
b OG = ‘Pennlate’ orchardgrass, RC = common reed canarygrass, SB = ‘Saratoga’ smooth bromegrass, Tim = ‘Climax’ timothy.
Adapted from Northeast Regional Publications 550, 554, 557, and 570. Management and Productivity of Perennial Grasses in the Northeast. West Virginia Agric. Exp. Stn.
Pre-joint High 3.2 3.3 3.0 3.3 54 100 22 32
Low 2.2 2.1 2.3 2.5 58 100 30 47
Early-head High 3.5 3.5 3.9 3.4 49 100 23 32
Low 2.0 1.9 2.9 2.4 57 100 30 32
Early-bloom High 3.6 3.7 4.9 3.9 51 100 25 14
Low 2.4 2.0 3.7 2.8 55 100 35 35
Late-bloom High 3.6 3.8 5.1 4.0 42 100 30 13
Low 2.5 2.0 4.0 3.6 53 100 38 40
Means of harvest schedules
Pre-joint 2.7 2.6 2.7 2.9 56 100 26 39
Early-head 2.8 2.7 3.4 2.8 57 100 27 32
Early-bloom 3.0 2.9 4.3 3.3 52 100 30 24
Late-bloom 3.0 2.9 4.6 3.4 48 100 34 26
Means of N rates

High 3.5 3.6 4.3 3.6 48 100 25 22
Low 2.3 2.0 3.2 2.7 56 100 33 38
Table 4. Nutritional value of perennial cool-season grasses at first harvest during spring and summer.
Stage at first harvesta Crude protein Digestible dry matter
OGb RC SB TIM OG RC SB TIM
---------- % ----------
a Grasses were fertilized with 200 to 250 lb N the previous year.
b OG = orchardgrass, RC = reed canarygrass, SB = smooth bromegrass, Tim = timothy
Adapted from Northeast Regional Publications 550, 554, 557, and 570. Management and Productivity of Perennial Grasses in the Northeast. West Virginia Agric. Exp. Stn.
Pre-joint 28.3 24.5 31.9 32.3 82 79 84 76
Early head 16.8 17.0 18.0 16.1 66 72 72 62
Early bloom 14.7 15.4 14.1 11.3 63 71 67 59
Late bloom 12.5 11.1 8.6 8.8 57 60 54 55

The aftermath crop similarly produces a growing point that is above ground approximately 5 weeks after the first harvest. If it is necessary to harvest the regrowth during the jointing stage of development, adjust the cutter bar above the growing point (4 inches) to assure a good third harvest. The quality of the aftermath harvests is only slightly affected by time of harvest.

Fertility

Fertility needs at seeding should be determined by soil test. Soil pH between 6.0 and 7.0 is best for smooth bromegrass, however it is adapted to slightly alkaline or acid soils (Table 1). In the absence of a soil test, assuming a medium-fertility soil, plow down 0-45-135 lb per acre and apply 20- 20-20 lb per acre at seeding (banded if possible). If bromegrass is seeded with a legume, reduce or eliminate nitrogen application at seeding.

Smooth bromegrass is very responsive to N fertilization and requires a high level of fertility for maximum production. If you plant smooth bromegrass with alfalfa or another legume, restrict N applications to 40 or 50 lb per acre to limit the effect N has on reducing nitrogen fixation of the legume. If smooth bromegrass is grown without a legume, apply 100 to 200 lb N per acre in split applications of 50 lb per acre in early spring when the grass becomes green and 50 lb per acre after each cutting.

Summary

Smooth bromegrass is a deep-rooted, sod-forming grass which grows best on fertile, well-drained soils with pH above 6.0. It will not tolerate frequent cutting. Spring harvest should be made before jointing or after the early-flower stage of development to ensure maximum smooth bromegrass persistence. This restriction on harvesting makes bromegrass unsuitable in mixture with alfalfa that will be harvested at the bud stage. However, mixtures with legumes that will not be harvested before 1/10 bloom are excellent. Smooth bromegrass is a good cool-season grass for Pennsylvania conditions but proper management is essential to obtain adequate yield and persistence.

Prepared by Marvin H. Hall, assistant professor of agronomy.

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Title

Smooth Bromegrass

Series

Agronomy Facts 27

Code

UC090

Cost

Free

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