Pastures are dynamic, ever changing and evolving. While many of us would believe that a pure stand of Kentucky bluegrass is best for our horses, you’ll find that is a difficult, if not impossible goal.
Different species thrive in slightly different environments, and mixed pasture stands are therefore the most durable from year to year. For example, Kentucky bluegrass enjoys close, frequent grazing, which is why it is so well-suited for horses, but it is the first to go dormant or die off during hot, dry summers. Tall fescue has the greatest tolerance of Kentucky summers, and holds its quality deeper into the winter, but it can’t tolerate shade. Orchardgrass thrives in shaded areas and comes up well when overseeded into existing stands, but only survives four to five years, sometimes less, under heavy grazing pressure. We can tailor our management to encourage mixed stands for stronger, more productive pastures.

Liming pastures

How we manage our soil acidity can influence what forage species are present in our pastures. For example, in a mixed pasture, adding lime to a soil with a low pH would tend to encourage the clover. If we did not add lime, we might expect grasses and acid tolerant legume species such as annual or sericea lespedeza to be present in greater quantities. Lime not only reduces soil acidity, but also makes other nutrients in the soil, like phosphorus and potassium, more bioavailable to the plant. If your pastures need lime as indicated by a soil test, then lime should be the first thing that you apply. In most cases, we should target a soil pH of 6.2 to 6.4 for grass-legume mixtures.

Fertilizing pastures

Generally speaking, improved grasses and legumes like orchardgrass, clovers and alfalfa need good soil fertility to persist and be productive. This means not only adjusting soil pH with lime, but also adding phosphorus and potassium. If soil fertility is low, it will favor species that are more efficient at extracting and using nutrients from the soil. A good example of this is tall fescue and sericea lespedeza on reclaimed mineland in southeastern Kentucky. These species are present because they are better adapted to marginal soils and poor fertility.

Nitrogen application rate and timing can also be used to shift the botanical composition of pastures. In mixtures of grasses and legumes, nitrogen fertilization will tend to encourage grass growth shifting the composition toward grasses and away from legumes.

The timing of nitrogen applications can also influence the balance of warm- and cool-season grasses in your pasture. Early spring and late summer applications will encourage cool-season grass growth (tall fescue and bluegrass). In contrast, late spring and summer applications will shift the pasture composition toward crabgrass, foxtail and nimblewill. Unless you are striving for warm season grasses to graze, fall nitrogen is best to maintain your cool season grasses.

Grazing management and forage plant growth

How we graze our pastures has a profound impact on botanical composition. To fully understand the effects of grazing management, we need to talk a little bit about forage plant growth. After defoliation (grazing or cutting), plants need energy to regrow. In grasses, this energy comes from two places. The first is leaf area remaining after grazing. The remaining leaf area is like a solar panel that captures sunlight and converts it into energy (sugars and carbohydrates) that the plant can use for regrowth. The more leaf area we leave, the larger the solar panel and the faster pastures will regrow.

The second place that energy comes from for regrowth is stored carbohydrates. The location of these stored energy reserves depends on the plant species. For example orchardgrass and tall fescue store their energy in the stem bases, while bermudagrass stores energy in its stolons and rhizomes (modified stems that grow just above or below the soil surface). So grasses that store their energy in the stem base are less tolerant to close and frequent grazing compared with grasses that store their energy in stolons and rhizomes that are safely below the grazing height of livestock.

The amount of stored energy in pasture plants depends on whether or not we rest our pastures between grazing events. Resting pastures allows leaf area to regrow and carbohydrate reserves to be stored up. In general, tall growing legumes are more dependent on stored energy for regrowth. For example, alfalfa is completely dependent on stored energy in the tap root for regrowth. This means that it needs time to rest and replenish its stored carbohydrates between grazing events. That is the reason that alfalfa does not persist well in continuous grazing systems.

Grazing height

In our naturalized pastures, close grazing will tend to favor grass and legume species that have leaf area and energy stores close to the soil surface. This results in a shift toward low growing species such as bermudagrass, Kentucky bluegrass and white clover under close grazing. A higher grazing height would tend to shift the botanical composition back toward our tall growing cool-season grass species such as tall fescue and orchardgrass.

Grazing frequency

How often we graze or if we utilize rotational stocking can influence the botanical composition of our naturalized pastures. Most pasture species benefit from rotational stocking. Some species are more tolerant of frequent grazing. These species tend to have leaf area close to the soil surface that is retained even under close grazing and include bluegrass, white clover and bermudagrass. This means that grazing naturalized pastures closely and frequently will tend to shift the botanical composition toward these species.

Grazing timing

The time of the season when pastures are grazed can also influence the botanical composition. Grazing a mixture that includes both cool- and warm-season species during the summer months will tend to shift the botanical composition toward the warm-season species. This commonly occurs in pastures in Western Kentucky. Grazing these pastures hard during the summer months favors the bermudagrass and crabgrass, especially during and after droughts.

Using improved varieties

After you determine what species are well adapted to your area and management practices, you may want to consider using improved varieties. These varieties may offer considerable benefits in terms of improved yield, animal performance and persistence. Using improved varieties of tall fescue, orchardgrass and white clover are particularly beneficial and highly recommended.

Regardless of what you are doing, in most cases working with nature greatly improves your chances of success. Grazing is no different. Successful grazing systems are based on forage species that are well adapted to your local conditions and managing those species to meet your specific needs.
To learn more about grazing management, please contact your local extension agent. They have a detailed understanding of local conditions and resources.

Chris Teutsch, PhD, UK Research and Extension Center, Princeton, Kentucky, and Krista Lea, MS, UK Horse Pasture Evaluation Program, Lexington, Kentucky, provided this information. Story adapted from article first published in Cow Country News, December 2020.