Summer annual forage grasses for emergency crops

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Summer annual grasses are used for summer pasture, green chop, hay, and silage. Annual grasses are normally used as emergency forage. The most common annual grasses used in Michigan are sudangrass, hybrid sudangrass, sorghum-sudangrass hybrids, and forage sorghum. A relatively new annual grass called teff, has been grown to a limited extent in Michigan with varying results, however, some growers have had good experience growing it.

Desirable characteristics, such as rapid growth, excellent drought resistance, and good response to fertilizer and water, make summer annual grasses attractive to use in an overall management scheme for forage production.


Sorghum-sudangrass hybrids produce about the same amount of feed as sudangrass when used for pasture. When used for green chopped forage, yields of sorghum-sudangrass hybrids usually exceed sudangrass or forage sorghum. Forage sorghums are best suited for silage. Making sorghum-sudangrass into hay is difficult because of the slow drying time. In 2007, Teff produced over 5 tons of dry matter at a demonstration in East Lansing under three cuts for hay.

Sudangrass and Brown Mid Rib (BMR) sudangrass

True sudangrasses have fine stems, tiller extensively when conditions permit, and can regrow rapidly. Thus, they are more suited to pasturing than other types of sorghum, and are more popular for annual hay and late summer pasture. Piper sudangrass is low in prussic acid content and has good drought and disease tolerance. It is a Wisconsin release that has good regrowth after pasturing and is the leading sudangrass hybrid. BMR sudangrass is more palatable and contains significantly less lignin making it more digestible than normal sudangrass.

Hybrid sudangrass

Hybrid sudangrasses result from a cross among true sudangrass strains that are available primarily as commercial varieties. They are similar to true sudangrass varieties, but yield slightly more in a three-cut green chop or hay system. Their prussic acid content is generally between that of true sudangrass and sorghum-sudangrass hybrids.

Sorghum-sudangrass hybrids

Sorghum-sudangrass hybrids are the most numerous of the various types of summer annual grasses. Most of these are available as commercial hybrids. They are high producing forage grasses, but more than 50 percent of their yield usually comes from their stems. Their rate of regrowth after repeated clippings or grazing is lower than that of sudangrass. Thus, animals graze or being fed sorghum-sudangrass hybrids sometimes result in less gain or milk production than those consuming other summer annuals, apparently due to lower energy content. When these hybrids are cut at immature stages, quality is higher, but yields are much lower.

Sorghum-sudangrass Brown Mid Rib

Brown Mid Rib (BMR) increased digestibility of the stems by reducing the quantity of digestible lignin. Lignin content is reduced approximately 40-60% depending upon environmental conditions. The reduction in lignin increases cellulose and hemicellulose content, both are more digestible than lignin. Since lignin is a structural component of the stem, its reduction stems are somewhat softer and more limber. BMR annual forage grasses should be planted at the same rate as Sorghum-sudangrass.

Teff

Teff, Eragrostis tef (Zucc.) Trotter, is a warm season annual grass native to Ethiopia(see figure 1 ). It is adapted to environments ranging from drought-stressed to waterlogged soil conditions. The seeds are extremely tiny, containing about 1.25 million seeds per pound. Despite its small seed size, teff is an aggressive competitor once established. In its native habitat maximum production occurs with a growing season rainfall of 17 to 22 inches and a temperature range of 50 to 85°F. Teff can be used as a livestock forage or pasture crop, and is primarily grown in Africa, India, Australia and South America. In the United States, teff is grown on limited acres in the Pacific Northwest and Midwest. Teff is a warm season annual grass which has shown good promise as an emergency forage crop in New York. Recent research from the Oregon State University Klamath Experiment Station and the Cornell Cooperative Extension Associations of Jefferson, St. Lawrence and Rensselaer Counties indicate good promise for teff as a forage crop.

Our teff demonstration planted in East Lansing in early July 2007 resulted in a dry matter yield of over 5 tons per acre dry matter with three cuttings. The forage quality of the hay showed crude protein of 15%.Seed of teff is available through many farm seed dealers in Michigan this spring. We will be evaluating teff in research trials in Michigan this summer comparing it to other warm season annual grasses and determining nitrogen application timing, and forage quality.

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Figure 1. Teff, Eragrostis tef (Zucc.) Trotter, is
a warm season annual grass native to Ethiopia.

Forage sorghum

Forage sorghums are usually tall growing, and mature late in the growing season. Often called “sweet sorghum,” forage sorghums often have sweet and juicy stems, and many have relatively small grain heads.

Forage sorghums usually yield more silage dry matter per acre than corn without irrigation. However, yields of total digestable nutrients (TDN) per acre are usually lower from forage sorghums than from corn.


Grazing forage sorghums is not recommended. They usually contain much higher levels of prussic acid than other summer annual grasses and can be dangerous to graze even when plants are completely headed, especially when young shoots are present. Forage sorghums can be cut for hay, although their stems dry very slowly after cutting.

Pearl millet

Pearl millet is a tall, warm season, annual grass. It originated in Africa and India where it was used for both forage and grain. It was introduced into the United States in the 1850s and became established as a minor forage crop in the southeastern and Gulf Coast states. Improved varieties or hybrids are generally leafier and shorter than older varieties. The solid stems are often densely hairy and usually 3/8 to 3/4 inch in diameter. Leaves are long, scabrous, rather slender, and may be smooth or have hairy surfaces. Leaves, as well as stems, may vary in color from light yellowish green to deep purple. A good stand of pearl millet will produce plants with relatively fine stems and profuse leafy growth. Pearl millet has a significantly higher leaf to stem ratio than other forages such as sudangrass, sorghum-sudan and foxtail millets.

The plant tends to tiller profusely under favorable climatic conditions and can compensates for uneven stand establishment. Prop roots arise from the lower nodes to help support the maturing plant. Regrowth potential after harvesting is comparable to sudangrass and much greater than foxtail millet.

Siberian foxtail millet

Siberian foxtail millet is the most commonly grown hay millet in the upper Midwest. It is a early maturing hay millet, ready for harvesting 55-65 days after planting. Siberian is extremely hardy and drought tolerant, making excellent quality hay.

German foxtail millet

German foxtail millet is a longer season type than Siberian, being ready to harvest 65-70 days after planting. German millet is taller with a coarser stem than Siberian. German millet can produce more forage than Siberian and because of its increased stem size it takes better management than other foxtail millets

Japanese foxtail millet

Japanese foxtail millet is distinctly different from other foxtail millets. Japanese is much taller and produces very coarse hay that contains fair feed value. This high tonnage annual forage works well in some rotations.

Utilization of Summer Annuals

  1. Summer pasture. Sudangrass and sorghum-sudangrass can provide supplemental summer pasture when cool-season grasses go dormant and the feed supply is short.

    Sudangrass and pearl millet produce better pasture than sorghum-sudangrass because they are usually leafier. They also provide a more uniform supply of feed for grazing and support higher daily gains or milk production. Sorghum-sudangrasses produce higher yields, but are better used to support livestock on maintenance or lower productivity levels.

    Graze the summer annual grasses in a short, rotational grazing system. Subdivide fields into three or more pastures so that each pasture can be grazed down in 7-10 days. Stagger the date of planting each pasture by about 10 days so that grazing will begin on each pasture when growth is at the appropriate height. This rotation system allows maximum production of quality forage.

    Graze sudangrass when it reaches 15-20 inches in height and sorghum-sudangrass hybrids when they are 18-24 inches tall. Danger from prussic acid poisoning will be low when grazing is delayed until grass is this tall. Graze down rapidly to 6 inches of stubble before moving livestock to a fresh pasture, and do not graze regrowth until 18 inches of growth accumulates. If growth is more than 36 inches tall, harvest as hay, green chop, or silage since grazing cattle will trample and waste much of the forage. Regrowth will be more rapid following cutting this taller growth, than if it is trampled.


    Summer grazing lasts about two months. During this time each acre of these pastures can provide feed for one to six mature dairy or beef animals. Grazing management and soil fertility and moisture will determine total production. Sudangrass, sorghum-sudangrass hybrids, and forage sorghum pastures are not recommended for horses because kidney ailments may develop.


  2. Green chop. Sorghum-sudangrasses are well suited to a green chop program. Under a 3-4 cut system, the forages produce higher yields than other summer annual grasses. Field losses are less from green chopping than from grazing or haying. However, the fast growth rate of sorghum-sudangrass results in variable amounts and quality of feed throughout the growing season. When grass is young and growing rapidly it may contain 20 percent crude protein and produce a highly succulent feed. As the crop grows taller and nears maturity, the protein content may drop to 7 percent or less, and fibrous, low quality green chop is produced. Nitrates can become a problem in a green chop program under certain growing conditions. Do not feed green chop that has heated in the wagon, feed bunk, or stack, or that has been held overnight. Nitrates are converted to nitrites as plants respire; nitrites are about 10 times more toxic than nitrates.

  3. Hay. For good quality hay, harvest sudans and sorghums before heads emerge or when they are 30-40 inches tall. These hays will contain slightly less protein than alfalfa hay and as much energy as good quality alfalfa hay. Use of a conditioner will aid in field drying. Field drying will usually take several days to dry to satisfactory levels.

  4. Silage. Forage sorghums for silage usually have about 75 percent of the energy value of corn silage per unit of dry matter, while other summer annual grasses have 60-75 percent of the value of corn silage. Most summer annuals need to be wilted or mixed with dry feeds to make satisfactory silage. Silage is often cut after frost to reduce moisture, especially with forage sorghums.

Seedbed preparation

A firm, well-prepared seed bed is needed for good seed-soil contact and rapid germination. Conventional, minimum, or no-till drilling can be used for establishment.

Date of seeding

Sudangrass and sorghum are warm-season grasses. Seed should be planted into soils when average soil temperature is above 60°F. Plan the seeding date to produce desirable feed when needed. Stagger planting dates to aid rotational grazing. It takes at least six weeks after planting before usable forage is available. Later plantings will result in lower yields due to summer droughts and fall frosts.

Planting rates

Recommended planting rates depend on row spacing. Broadcast and narrow-row spacing are preferred for sudangrass and sorghum-sudangrass hybrids because they result in shorter plants with finer stems. Total forage yield will be similar for different row spacing because sorghums and sudangrasses tiller. Removing the primary growing point at the first cutting enhances tillering. First-cut yields are usually higher for broadcast or narrow-row seedings than for 20- 40 inch rows. If planting with a grain drill, plant 15 to 20 lbs/acre seed of pearl, German, Japanese or Siberian millet. Forage sorghums should be planted at 12-15 lbs/acre with a grain drill. Use 6-12 lbs/acre for pearl millet. Sudangrass and sorghum-sudangrass are seeded at 20-30 lbs/acre in 7 inch rows with a grain drill. Higher seeding rates help in producing finer stems, which is desirable for grazing and hay.

Planting depth

Seed to a depth of 1-2 inches, depending on soil moisture conditions. Seeds planted too deep do not emerge well and poor stands may result.

Fertilization

Summer annual grasses have fertilizer requirements similar to those of corn. With rapid growth, apply sufficient nitrogen at planting to ensure establishment and high first-cutting or grazing yields. Apply 40-80 pounds of nitrogen per acre at planting and an additional 50 pounds after the first cutting or grazing. Phosphorus and Potassium should be applied based upon soil test recommendations.

Prussic acid poisoning

Cellular damage to sorghums and sudangrasses from frost, wilting, bruising, drought, excessive soil nitrogen, or deficiencies in soil phosphorus or potassium can result in prussic acid poisoning in cattle. Prussic acid poisoning consists of the following sequence of events: plant cells rupture and cyanic acid (HCN) forms from cyanogenic glycosides; cattle consume forage with elevated HCN levels; HCN is absorbed from the rumen; HCN binds to hemoglobin; asphyxiation and death occur. Poisoning is most likely after a frost when animals consume the leafy regrowth. Regardless of season, plants less than 18-24 inches tall should not be grazed. Suspect forage should be harvested as dry hay or silage. Both harvest methods tend to reduce hydrocyanic acid levels.

Nitrate poisoning High dietary nitrate levels can overload the animal’s ability to detoxify this chemical and can result in death due to asphyxiation. In the rumen, nitrate is reduced to ammonia, which is absorbed into the bloodstream or converted into microbial protein. High dietary nitrate levels that overload this microbial reduction system cause an accumulation of nitrite in the rumen. This nitrite is then absorbed into the bloodstream where it binds to hemoglobin in place of oxygen. This deprives the tissues of oxygen and causes abortions and asphyxiation.


Sorghums and sudangrasses can accumulate high levels of nitrate during environmental conditions that decrease plant growth rate, including water stress, lack of sunshine and high nitrogen fertilization. Plants usually absorb nitrogen as nitrates and synthesize protein. However, during stress, the synthesis rates decrease and nitrates accumulate. Cattle should not be fed forages with nitrate levels greater than 2 percent. Nitrate analysis can be obtained from numerous commercial laboratories.

Seed availability

Most commercial suppliers of seed carry varieties of sorghums, sudangrasses, BMR sudangrass, hybrid-sudangrasses, and sorghum-sudangrass hybrids, Sorghum-sudangrass BMR, and millets. Check with your local supplier for availability and variety characteristics. Because of low hay carryover from last year’s crop, there will be higher demand for annual forage crops. Michigan State University does not routinely test varieties of annual grasses and therefore does not provide variety recommendations.

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