Extending the Grazing Season with Plant Diversity

Grazing is a cost-effective method to nourish ruminant animals. Research has shown that the cost of harvested-stored fed forages is at least twice as much as that of grazed forage per ton of dry matter. The challenge for graziers is to maximize the duration of the grazing season and limit the amount of stored forage used. New advances in grazing methods, species selections, and forage establishment methods create exciting new opportunities to use many different annuals and perennials in crop rotations to expand the grazing system.

Grasses, legumes, and nonleguminous broadleaves can be classified as perennial and annual cool- and warm-season species (see Table 1).

Cool-Season Perennials: The Mainstay of Northeast Graziers

Cool-season perennial grasses are the mainstay of grazing systems in the northeastern United States. Common species are orchardgrass, timothy, and canarygrass. However, there are many other grasses that can be used (see Table 1). Cool-season legumes are often included in cool-season perennial mixes to fix atmospheric nitrogen, so nitrogen fertilizer use can be reduced or eliminated. Legumes also tend to maintain forage quality, while grasses decrease in forage value as soon as they start to go reproductive. Common cool-season perennial legumes used in pastures are red and white clover. Alfalfa can also be grazed and is used in mixtures. Perennial nonleguminous broadleaves can also be used as part of grazing mixtures, although they are not commonly included.

Research from the USDA-ARS Pasture Research Laboratory has shown that inclusion of chicory in a perennial cool-season stand can improve soil organic carbon content at depth and improve productivity. The taproots of species such as alfalfa and chicory can help improve subsoil macroporosity. But it is hard to maintain the desired broadleaves in the stand, as they often disappear with time.

The big challenge for graziers in the Northeast is the reduction in growth of cool-season perennial pastures in the summer when temperatures exceed 80°F and the difficulty of grazing in the winter. Cool-season perennials have a peak in production in the spring and another peak in the late summer/early fall (Figure 1). Most graziers either understock in the spring and fall to have sufficient grazing in the summer, or they overstock. If they understock, they are almost forced to harvest some of their paddocks for hay or haylage in the spring and sometimes in the fall as well. If they overstock, then they have to buy hay or haylage to supplement insufficient forage from pasture during a time of low production.

By complementing cool-season perennial pastures with warm-season annuals and perennials and cool-season annuals, the grazing season can be extended, which helps reduce costs of feeding. At the same time, it helps reduce the danger of overgrazing pastures in the summer. Some cool-season perennials are suited for stockpiling. This is the practice of resting a pasture in the late summer so the standing biomass can be grazed in the fall and winter.

The Challenge of Grazing Only Cool-Season Perennials

Table 1. Perennial and annual warm- and cool-season species that can be used for grazing.

Perennial Grasses: Cool-Season Species

• Orchardgrass
• Timothy
• Perennial ryegrass
• Tall fescue
• Meadow fescue
• Red fescue
• Chewings fescue
• Festulolium
• Meadow brome
• Smooth brome
• Canarygrass
• Bluegrass
• Intermediate wheatgrass
• Virginia wildrye

Perennial Grasses: Warm-Season Species

• Switchgrass
• Big bluestem
• Little bluestem
• Indiangrass
• Coastal panicgrass
• Eastern gamagrass

Perennial Legumes: Cool-Season Species

• Alfalfa
• Red clover
• White clover
• Alsike clover
• Yellow sweetclover
• Strawberry clover
• Birdsfoot trefoil
• Sainfoin
• Crown vetch

Perennial Legumes: Warm-Season Species

• Maryland senna
• Showy tick trefoil
• Panicled tick trefoil
• Dillonius tick trefoil

Perennial Nonlegume Broadleaves: Cool-Season Species

• Chicory
• Narrow leaf plantain

Perennial Nonlegume Broadleaves: Warm-Season Species

• Cupplant

Annual Grasses: Cool-Season Species

• Barley
• Annual ryegrass
• Cereal rye
• Oats
• Triticale
• Wheat

Annual Grasses: Warm-Season Species

• Sudangrass
• Sorghum-sudangrass
• Pearl millet
• Corn
• Forage sorghum
• Teff
• Japanese millet

Annual Legumes: Cool-Season Species

• Crimson clover
• Hairy vetch
• Common vetch
• Deer vetch
• Partridge pea

Annual Legumes: Warm-Season Species

• Soybean
• Cowpea
• Lentil
• Sweet blue lupine
• Trailing wild bean
• Mungbean
• Lablab bean
• Sunn hemp

Annual Nonlegume broadleaves: Cool-Season Species

• Radish
• Turnip
• Rape
• Kale
• Swede

Annual Nonlegume broadleaves: Warm-Season Species

• Sunflower
• Buckwheat
• Squash

Warm-Season Annuals to Meet Grazing Needs in the Summer

Warm-season annuals are adapted to the heat of summer and can therefore be used to meet grazing needs during the summer by grazing them either several times or only one time. They don't readily germinate until soils are at 65°F and grow well at temperatures up to and even exceeding 90°F. Some prime warm-season grasses suited for grazing two or three times in the summer are sudangrass, sorghum-sudangrass, and pearl millet (Figure 2; see also Table 1). These species are adapted to hot and dry conditions. 

Meeting Grazing Needs by Integration of Diverse Crop Types

Sudangrass and sorghum-sudangrass are typically more productive than pearl millet varieties. However, sudangrass and sorghum-sudangrass pose a danger of prussic acid accumulation under stress. Stress can be due to drought or frosting. Pearl millet does not produce prussic acid and is therefore preferred by some producers. Nitrate concentrations can also increase to undesirable levels if these grasses are heavily fertilized or during droughty periods, so nitrates need to be monitored, too. The quality of warm-season annuals is good when grazed in the vegetative stage, but it decreases rapidly when they start to head out. Therefore, it is important to graze them regularly to keep them in the vegetative stage. Some graziers even clip the pastures after grazing to guarantee uniform regrowth and avoid some patches of the pasture that were not grazed from going to head.

On the other hand, these forages should not be grazed too low to the ground to ensure quick regrowth— leaving a residue of at least 6 inches for most warm-season annuals is desirable. It is essential that enough plant residue is left after grazing to guarantee quick regrowth. The residue left constitutes a solar panel for photosynthesis to guarantee quick regrowth, while part of the biomass that is trampled onto the soil serves an important role for soil protection and as feedstock for soil organisms such as earthworms, arthropods, protozoa, fungi, and bacteria. These soil organisms are a crucial component of keeping soil productive by recycling nutrients and restoring porosity and aggregation after grazing. Other warm-season annual grasses include teff, which is also drought resistant, and Japanese millet, which is adapted to poorly drained soils.

Meeting Grazing Needs by Integration of Diverse Crop Types

While these species can be grazed several times during the summer (on average every 20 days), it is also possible to plan for one grazing of warm-season annuals in the late summer (Figure 3). This is not to overcome the summer slump in cool-season pasture production, but it can be an option to enable some cool-season perennial pastures to rest for stockpiling later in the fall or winter. In this case, mixtures can include corn, forage sorghum, sunflowers, cucurbits, soybeans, and cowpeas. These species don't grow back after grazing, so they are not suited for repeat grazing in the summer, but can be used in a one-graze setting at the end of the summer.

It is challenging to maintain production of lactating dairy cows on a diet of pure warm-season grass, but if their diet is supplemented, it is possible to maintain good milk production. Nonlactating dairy cows and beef cows can be fed successfully with warm-season annuals. Warm-season annual grasses can be mixed with legumes or nonleguminous broadleaves to improve their feed value. However, our experience is that these grasses often compete so heavily with the broadleaves that the broadleaves end up comprising only a small part of the mix.

If a mix is desired, then low rates of warm-season grass should be used. If using warm-season annual legumes, make sure to inoculate them with the proper rhizobium strain because the rhizobium is not likely to be in the soil if similar legumes have not been grown there before. Warm-season annuals should be established in late May/early June when soil temperatures reach 65°F. This means they can be no-tilled into a cool-season perennial field that was grazed heavily and subsequently killed with herbicide or after a cool-season annual has been grazed in the spring.

Cool-Season Annuals as Rotation Crops with Summer Annuals and Perennial Pastures

Cool-season annuals can also add to the diversity of forages to extend the grazing season. They fit well because they can be grown after a warm-season annual as part of a rotation with perennial cool-season species. Some farmers use one or two years of a sequence of warm-season–cool-season annuals as part of a pasture renovation program. The cool-season pasture can be maintained for four to six years, after which it is rotated out for one or two years before an improved cool-season perennial mixture is seeded again. This is attractive because it is easier to control the old vegetation completely when annuals are grown for a year or two. If cool-season annuals are planted in late summer (typically six weeks before the first hard frost date), it is possible to graze them once or several times in the fall. In this case, oats or another cool-season annual such as turnip or radish that does not need vernalization (a cold period to start the reproductive stage) can be a good choice—oats particularly produce more growth in the fall than species such as rye if planted early.

However, the oats winterkill, so it is desirable to mix them with an overwintering species that can be grazed in the spring. Mixing oats with rye, triticale, annual ryegrass, or cool-season annual legumes such as crimson clover or hairy vetch can help guarantee a spring grazing from the same cool-season annual planting. Determining the seeding rate is a bit of a balancing act because if too much oat growth results, it may suffocate the overwintering annuals and reduce their growth in the spring. Because every fall is different, the results may vary from year to year. If establishment of the cool-season annual mix is not possible in late summer, it is better to plant winter-hardy species only and not to count on fall grazing, but only for one or several spring grazing events (Figure 4). The later in the fall it gets, the smaller the repertoire of suitable species becomes until only rye, wheat, and triticale are left as choices in the late fall.

Cool-season annuals typically have high nutritional value and can be very high in protein and digestibility and are therefore suitable as feed for lactating dairy cows. It may be desirable to supplement animals grazed on these pastures with some fiber or energy to balance their diet.

Meeting Grazing Needs with Cool-Season Annuals

Source: Marvin Hall, "Warm-season Grasses" (University Park: Penn State Extension, 2008).

Warm-Season Perennials: A Perennial Choice to Meet Summer Pasture Needs

Warm-season perennial grasses have not been widely used in Pennsylvania for forage, but research has shown that they can also be successfully included in a grazing program. Warm-season perennial grass species include switchgrass, big bluestem, little bluestem, indiangrass, and others. They are highly adapted to warm temperatures, some are extremely drought-resistant, and some are adapted to poorly drained soils. Therefore, they could be used to alleviate the summer slump in cool-season pasture production. These grasses are known for their large root systems, which are believed to be the reason for the high organic matter of (former) prairie soils in the midwestern United States and elsewhere. Warm-season perennial grasses are therefore highly suited to improve soil health. They are not suitable for lactating dairy nutrition, but they can be used to feed heifers, dry cows, and beef cows. Digestibility of warm-season grass was found to be similar to that of orchardgrass in the vegetative stage.

Research from Missouri showed that crude protein content was 15 percent early in the growing season, decreasing to 8 percent in late August. The grazed yield of a mixed switchgrass/big bluestem/ indiangrass field on a farm in Forest County in July and September 2017 was 4.7 tons per acre, while about 1 ton per acre of standing biomass was left after each grazing. The USDA-ARS Pasture Lab recorded average yields of 3 to 3.8 tons per acre (Table 2). Warm-season perennial grasses produced high yields even on shallow soils, while cool-season perennials took a big hit on those soil types, showing the drought resistance of species such as switchgrass and big bluestem. They are typically hard to establish because they grow very slowly in the first year after establishment, during which they are often heavily infested by weeds. It is therefore recommended to use a field that has low weed pressure (e.g., after a sequence of warm- and cool-season annuals with good weed control). Once a successful stand has been established, it can be productive for several decades if managed well.

Some key attributes of different warm-season grasses are summarized in Table 3. For Pennsylvania, yield is a major factor, but so are adaptation to droughty or poorly drained soils, ease of establishment, and feed value. Although warm-season perennial grasses can be mixed, this has to be done with some thought because these grasses mature at different times of the year. It is recommended to graze a grass in the boot stage, just before it starts heading. That is because at that time, forage quality is still good and yield is high. If the grass is grazed earlier, yield is sacrificed and the stand weakened. If the grass is grazed at maturity, the quality is very poor, which affects daily gain of the grazing animals. Therefore, mixing an early maturing species such as switchgrass with late maturing indiangrass, for example, is not recommended because when one species is ready to be grazed, it is still too early for the other species or the other species is too mature for adequate animal nutrition.

Conclusion

The advent of no-tillage has made it possible to efficiently establish a new stand without harming soil health. This has opened exciting opportunities to rotate cool-season perennials, which remain the mainstay of grazing in the northeastern United States, with warm-season annuals for grazing in summer and cool-season annuals for grazing in fall and spring. Warm-season perennial grasses can also be integrated in a grazing program, but because most are hard to establish, they should be managed to keep them in production for a long time. By developing a grazing plan that integrates cool-season perennials with warm- and cool-season annuals and warm-season perennials, the grazing season can be extended significantly while overgrazing will be avoided and soil health will be maintained.

Source: "Grazing Native Warm-Season Grasses in the Mid-South," SP731-C (University of Tennessee Extension).

Source: Adapted from "Native Warm-Season Grass Pastures" (Missouri Department of Conservation).

Prepared by Sjoerd W. Duiker, professor of soil management and applied soil physics, and Jessica A. Williamson, assistant professor of forage management.