UT Extension News: “Using Native Warm Season Grasses for Forage”

June 30, 2020

by Chris Hicks, County Director – UT Extension Smith County

Last week I discussed some of the most common native warm season grasses (NWSG). These grasses have historically been thought of as being excellent habitat for wildlife, due to the structure of cover they provide. They have also been looked at for their ability to provide cellulose which can be used in ethanol production. While these are two exciting uses for these grasses, livestock producers should be aware that many of the NWSG make excellent forages due to their drought resistance, time of maturity, and high yields. 

NWSG are attractive as a forage crop because they produce the majority of their growth during the summer, when cool-season grasses produce relatively little. Depending on the species grown, rainfall, soil type, and other conditions, yields of two to five tons per acre can be expected. Switchgrass and eastern gamagrass typically have yields of 4-5 tons of forage per acre, compared with tall fescue which averages 2.5-3 tons per acre. While yields can be reduced in dry summers, NWSG are less sensitive to drought than cool-season grasses and yield reductions will not be as explicit.

Crude protein can be as high as 16–17 percent, but normally is 8–12 percent at optimum harvest. Just as with any forage species, nutrient content of NWSG is influenced by plant maturity. As plants mature, percent protein and digestible energy decrease, while fiber content increases. Maximum tonnage and high forage quality do not occur at the same time. In relation to plant maturity, the forage quality of NWSG deteriorates faster than with cool season grasses, therefore timing of the harvest is even more critical. Whether dealing with cool season or warm season grasses, hay should be cut before the seedhead emerges, but this is especially important for warm season grasses.

A major advantage that NWSG have over cool season grasses is that warm weather makes better haying conditions. High temperatures and low humidity decrease drying time, which results in less nutrient loss. There is less chance that rain may delay harvest, and once the hay is cut, higher temperatures enable hay to dry faster, resulting is less respiration and leaching loss. Oftentimes a bale of switchgrass or eastern gamagrass will be better quality than a bale of tall fescue, not because these varieties are better species’, but because hay-making conditionsare better during theirgrowing season andbecause rain and cool temperaturesoften delay cutting tallfescue.

Switchgrass and eastern gamagrass are regularly planted in pure stands for haying or grazing. These grasses are commonly hayed from mid-to late May for an optimum hay quality-to-tonnage ratio. Mixtures of big and little bluestem and indiangrass are frequently grown together and are normally hayed in late June. In most cases, a second cutting can be taken from NWSG about four weeks after the first cutting. NWSG can also be used for grazing during the summer. By converting 25 percent of the pasture acreage to NWSG, animals may be grazed on actively growing forage during the summertime, which can provide higher-quality forage while allowing cool-season grasses to rest.

Management of NWSG is critical for their establishment and continued success. Cutting height is extremely critical to maintenance of stand vigor and longevity. Cuts below 8 inches reduce quality by increasing steminess of the hay, therefore an 8-inch harvest height is recommended. Also, NWSG need time at the end of the growing season to fully restore carbohydrate reserves for the winter dormancy period. Previously hayed NWSG should be 12–18 inches tall before fall dormancy; therefore, a good rule of thumb is to rest the stand after September 1 at the latest, with early August being preferable.