Transition pastures with warm-season annuals
|By Jeff Lehmkuhler|
Sorghum-sudangrass, sunflower and cowpea mixture planting to be grazed by beef cows during the transition from fescue to another forage species.
The author is an extension beef cattle specialist at the University of Kentucky.
Tall fescue comprises the main forage species in pastures in the upper transition zone. Much of this fescue contains an endophytic fungi that provides improved pest and drought persistence. However, the alkaloids produced by the fungus have negative impacts on animal production, which significantly costs the beef industry.
Interest in alternative forage species as well as newer fescue varieties with novel endophytes that do not have the negative impacts on livestock production are increasing.
During pasture renovation of old tall fescue pastures, a spray-smother-spray approach is generally recommended. The smother aspect is often a warm-season annual that provides forage production during the renovation process. Sudangrass, forage sorghum and sorghum-sudangrass hybrids have long been utilized to provide high yield and good quality forage during renovation. The availability of brown mid-rib (BMR) varieties provides an option for improved quality and animal performance.
Research is promising
Texas researchers observed a 0.3 pound per day advantage for a BMR sorghum variety when grazed by beef steers compared to a similar non-BMR sorghum variety. This translated to a 37 pounds per acre increase in beef production.
Photoperiod-sensitive varieties that delay flowering until later in the growing season when day length is shorter are also available. These varieties provide greater flexibility in harvest windows by delaying maturity. Photoperiod-sensitive sorghum-sudangrass hybrids can also be used in combination with climbing warm-season legumes.
Warm-season annual legumes often considered include cowpeas, lablab beans, lespedeza and soybeans. Cowpeas and lablab beans can be quite productive in semiarid regions. These legumes can produce forages with quality similar to alfalfa. Percentage crude protein can be in the low 20s, neutral detergent fiber percentages are often in the upper 20s to low 30s range with fiber digestibility in the high 50s to low 60s. Yields can range from 1.5 to 2.5 tons of dry matter per acre for lablab beans and cowpeas.
Many annual legumes can be used in combination with annual grasses. In one study, lambs grazing cowpeas were found to have greater performance in three of four years compared to lambs that grazed sudangrass or were fed hay and a 16 percent crude protein supplement. Legumes will climb and are ideally suited for use with photoperiod sensitive sorghum-sudangrass or grazing corn to provide additional protein and improved digestibility.
Some researchers have noted that cattle selectively consume the large leaves of lablab beans as plant maturity advances. In addition, as forage availability fell below 1,000 pounds of dry matter per acre, performance declined. Soybeans can also be utilized as a warm-season annual legume, providing 3 to 6 tons of dry matter per acre and high digestibility.
Lessons learned from my farm experience using warm-season mixtures include the importance of seed drill calibration, as these mixtures won’t be found in the user’s manual. Winter annual forages need to be sprayed out as they compete with the establishing forages; this occurs even after cutting the winter forage for hay prior to planting. To avoid high forage nitrate levels in sorghum-sudangrass hybrids, residual nitrogen from corn fields and legume-based sod pastures need to be credited and application rates adjusted accordingly.
Cowpea and lablab beans will regrow after grazing and haying, but they may not grow as fast as the grass component and contribute less than expected. Plant cowpeas and lablab beans at rates of at least 30 pounds per acre to have sufficient legume contributions (20 to 30 percent of the total plant population).
Cattle do not graze sunflowers, which are best suited for haying. Extremely wet conditions can lead to pugging and soil compaction; keep cattle off crop fields until conditions improve. Even with some nitrogen and weather challenges, producers have been able to get 50 to 75 cow-grazing days per acre on fields planted to these annual forages.
Using warm-season annuals is an option for beef producers to provide grazing during the transition to a more productive permanent pasture. These forages can be grazed in about 45 days following planting with subsequent grazings approximately every four weeks. Delay planting until soil temperatures are near 60°F for best establishment. In regions where summer precipitation is limited, millets may be a better option to eliminate the risk of cyanide poisoning.
Several options exist for combining warm-season forages. Good forage quality and yields combined with reasonable cost of production provide alternatives for beef cattle producers to mitigate the summer slump of cool-season forages and reduce the risk of fescue toxicosis. •This article appeared in the November issue of Hay & Forage Grower on page 28.
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