Ryegrasses are the most widely grown cool-season grasses in the world. They have numerous desirable agronomic qualities.
They establish rapidly, have a long growing season, are high yielding under favourable environments when supplied with adequate nutrients, possess high nutrient contents, and can be grazed and used for hay or silage.
Ryegrasses grow best on fertile, well-drained soils but can be grown on soils where it is too wet at certain times of the year for satisfactory growth of other grasses (Table 1).
Ryegrasses are heavy users of water and their performance is less than optimum during a drought or periods of extended low or high temperatures.
They are indigenous to Europe, Asia, and North Africa, but are grown worldwide. The ryegrasses are considered to be high quality forage and their high digestibility makes them suitable for all types of ruminants.
Types Of Ryegrasses
The two most important ryegrass species are Italian ryegrass (Lolium multiflorum Lam.) and perennial ryegrass (Lolium perenne L.). Traditionally, Italian ryegrass would not survive for more than a single growing season in northern climates. However, new experimental varieties from Switzerland have shown no stand loss after three production years in Pennsylvania.
Italian ryegrass has a bunch-type growth (lacks rhizomes) and flowers in day lengths greater than 11 hours. There is no winter or cold weather requirement for Italian ryegrass to flower and, therefore, it flowers throughout the summer. Italian ryegrass is not widely recommended as a forage crop in Pennsylvania because available varieties do not survive Pennsylvania winters.
Perennial ryegrass is also a bunch-type grass, but it generally survives for several growing seasons in Pennsylvania. Unlike Italian ryegrass, perennial ryegrass requires a dormancy period of cool temperatures before the photoperiod can induce flowering and, therefore, normally produces seedheads only once per year, during the late spring.
However, researchers at Penn State have observed seedhead production by perennial ryegrass during midsummer regrowths. Perennial ryegrass can withstand considerable grazing mismanagement and remain productive.
Unfortunately, perennial ryegrass has proven to be slightly less persistent in the Pennsylvania climate than are other cool-season grasses such as orchardgrass, tall fescue, and timothy. There are two basic groups within the Italian and perennial ryegrass species, the diploids and tetraploids.
The distinction between the two groups is based on the number of chromosomes within each plant cell. In the diploid ryegrass cells, each chromosome is present twice; however, in the tetraploid ryegrasses cells each chromosome is doubled and is present four times.
Of the two groups, tetraploid perennial ryegrasses have larger leaves, fewer but larger tillers, produce a more open growth (less ground cover), and are more suited for production in a legume mixture.
Tetraploids have a higher percentage of sugars in their forage than are found in diploids, which explains their higher digestibility and why animals graze them in preference over diploids. Both the seed and seedlings of tetraploid varieties are larger, but the growth following emergence and persistence is often greater for diploid varieties.
Numerous tetraploid perennial ryegrasses have been tested in Pennsylvania variety trials, including Grimalda, Bastion, Reveille, Citadel, Nestor, and Taptoe. Grimalda matures 10 to 14 days earlier than Bastion, Reveille or Nestor. Citadel and Taptoe mature later than these varieties.
Grimalda was one of the first ryegrass varieties marketed in Pennsylvania. Unfortunately, it matured earlier than most alfalfa varieties with which it was seeded and reduced the forage quality when the harvest date was based on alfalfa maturity. The experience with this early maturing variety resulted in producers concluding that all ryegrasses were not adapted to their system, a conclusion from which perennial ryegrass is now starting to recover.
Natural hybridization between the Italian and perennial species has occurred frequently. Because their persistence is intermediate between the parents, hybridized ryegrasses are frequently referred to as “short-rotation ryegrasses,” relative to perennial ryegrasses.
In addition, flowering of the hybridized ryegrasses is similar to that of the Italian species because there is no dormancy requirement for flowering and because tillers will continue to flower sporadically throughout the growing season. Bison, a hybridized ryegrass tested in Pennsylvania, matures in the spring about 10 days after Grimalda.
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