Ryegrass roundup

Rye is a staple forage in Southern pastures. Well, ryegrass, that is — not cereal rye. More specifically, annual ryegrass is the crop in question, not the perennial kind. And just to be clear, we are definitely not talking about rye bread.

Despite the species name debacle, Mike Trammel with Oklahoma State University says annual ryegrass is not to be confused with perennial ryegrass or cereal rye. Perennial ryegrass is predominately grown in mild Northern climates, whereas cereal rye is a small grain. Although annual ryegrass and cereal rye both tend to be referred to as “rye,” the two species are quite distinct.

Every year, annual ryegrass is interseed into over 2 million bermudagrass and bahiagrass acres in the South to extend either shoulder of the grazing season. More than a million additional acres are seeded as a stand-alone annual forage or a cover crop in the fall that remains productive until late May or early June. Annual ryegrass is also used in pasture mixes to reduce the risk of bloat from legumes.

Annual ryegrass has dark green, shiny leaves that have smooth edges. Trammel notes it is adapted to a wide range of soil conditions, from poorly drained clays to deep sands. The extension area agronomist says annual ryegrass will grow in areas that receive as little 20 inches of rain a year, although production is greater in regions with higher rainfall.

“In Oklahoma, the best ryegrass production area is east of I-35; however, annual ryegrass can produce well in many years from southwest Oklahoma north to Kansas in rainfall belts of 25 inches or more,” Trammel writes in a recent Cow-Calf Corner newsletter. “It will also grow on acid soils, although growth is limited when the soil is below a pH of 5.5,” he adds.

Tetraploid versus diploid

To further classify annual ryegrass, Trammel explains the difference between tetraploid and diploid varieties. Diploid ryegrass contains two sets of chromosomes, whereas tetraploid ryegrass contains four. These mutant hybrids were discovered by scientists in the 1930s before being developed by Netherland researchers. The first tetraploid varieties were introduced in the United States by German plant breeders in the 1960s.

Trammel notes tetraploids have larger tillers, wider leaves, and generally grow bigger than diploids; however, long-term yield data shows little difference between tetraploid and diploid varieties in most locations.

In a Mississippi grazing trial, cattle did prefer tetraploid ryegrass to diploid ryegrass, consuming the former variety 54% faster than the latter. With that said, another study shows stocker steers on tetraploid ryegrass did not have higher average daily gain or greater gain per acre than those grazing diploid ryegrass.

“The conclusion from all this research is that there is more difference within diploid and tetraploid varieties than there is between them,” Trammel says. “Look for a high-yielding variety that is recommended for your area and disregard the ploidy level,” he asserts.

Other characteristics to look for when selecting ryegrass seed include adequate winterhardiness, good germination, and a high percentage of pure live seed. Trammel adds that even though tetraploid seed is 50% to 100% larger than diploid seed, seeding rate recommendations are the same. These are generally 25 to 30 pounds per acre for broadcast seeding or 20 to 25 pounds per acre if seed is drilled. Be sure to calibrate drills according to seed size.