There are over 60 varieties of annual ryegrass commercially available that are grouped in two different types based on their number of chromosomes (ploidy level). These two types include diploid and tetraploid varieties. Diploid varieties have to set of chromosomes (2n = 14) in each cell, their cells are smaller in size with lower water (moisture) content, plant structures (leaves and seed size) are smaller, and the plant tend to produce more tillers. Higher tiller density can provide a denser stand and be more competitive with weeds, sustain production in lower fertility and wetter soils. Diploids also tend to have more a prostrate growth (horizontal) which allows the stand to be more persistent in heavy grazing scenarios. On the other hand, tetraploid varieties have four set of chromosomes (4n = 28) in each cell with larger cell size, larger (wider) leaves, larger seed size, greater content of soluble carbohydrates (sugar and starch) and less fiber content. Tetraploid varieties are developed by treating germinating seed with specific compounds that cause a mutation in the chromosome number. Tetraploids tend to have higher water content in their cells and therefore animals can fill up faster and reduce dry matter intake. Tetraploids have a slower recovery after grazing than diploids because they do not tiller as aggressively and they can also be susceptible to overgrazing because of higher palatability which can lead to overgrazing. Since tetraploids do not tiller vigorously as diploids, they could be good candidates for mixtures with clovers and reduce species competition. In general, tetraploids tend to mature later than some diploids. Although these differences between annual ryegrass types may not be obvious early in the season, they can become more apparent as the season progresses and grazing pressure is implemented.
Yield measurements from the variety trial are extremely important in determining the number of acres to plant, the amount of fertilization needed and the number of animals that grazing system can sustain. Knowing average yields will allow forage/livestock producers to better match nutrient applications to minimize costs, maximize fertilizer efficiency and reduce potential environmental problems. Yields are also critical as a measuring tool to evaluate new varieties, improve management techniques and allow producers to make more informed decisions concerning feeding practices for their livestock. Knowing the estimated forage for winter grazing would allow producers to buy or sell forage at the time of the year that would be most financially feasible. When available, using data from multiple years as an average might provide a better assessment on varietal performance than a single year, due to changes in weather conditions, especially temperature and precipitation that could affect production from year to year. Data summarized in Table 1, provides a better assessment of annual ryegrass production across three locations in the state. An average yield of annual ryegrass yield ranges from 5,630 pounds per acre in Starkville, MS to 6,332 pounds per acre in Poplarville, MS. The state average dry matter yield was 5,956 pounds per acre. The overall yield potential of annual ryegrass was below the state average for Starkville and Newton, while the largest increase in yield potential has been observed in Poplarville. Performance of varieties across the state also indicated that 25% of the diploid and tetraploid varieties had a relative lower yield (RY) compared to the state average production. Click here for more information on Mississippi State Forage Variety Trial.
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