By Vanessa A. Corriher
Managing for drought is complex and must take place throughout the calendar year. Be sure to graze properly in the summer and plan ahead for fall, winter and spring forage production so that feeding of expensive hay or supplements is minimized.
Summer annual grasses should be temporary solutions to summer forage needs. They can be expensive to produce and difficult to manage, and have a potential for prussic acid and nitrate poisoning of livestock. Some desirable characteristics include rapid growth, excellent drought tolerance and good response to fertilizer and water. The most efficient and economical use of these grasses is in a management-intensive rotational grazing system.
Some examples of summer annual grasses are: sudangrass (sorghum bicolor), forage sorghum (sorghum bicolor), sorghum-sudangrass hybrids, pearl millet (Pennisetum americanum) and crabgrass (Digitaria sanguinalis). Each of these forages has unique growth characteristics that require proper management for optimum production.
Choose the right forage for your operation. Pearl millet is better adapted to sandy, acid soils than forage sorghums, and will regrow after harvest if a 5" stubble height is left. Grazing can be continued until frost is expected. Pearl millet has a distinct advantage compared with sorghum, sudangrass and sorghum-sudangrass hybrids, because it does not produce prussic acid. However, millet as well as sorghums can cause nitrate poisoning.
Sorghums are a class of warm-season annual grasses in which several forage types have been developed. Forage sorghums are best adapted to fertile, well-drained soils that have good water-holding capacity. It is the most drought-tolerant of the warm-season annuals that we have mentioned. Before grazing, sorghum should be at least 30" tall and grazed to a stubble height of 5" to 7". Forage sorghums are best used in a single hay cutting when plants are in bloom or early dough stage. A mower-conditioner will be needed to crush the stems to decrease drying time.
Sudangrass is a rapid-growing, warm-season annual that can produce good-quality forage if it is managed appropriately. True sudangrass has fine stems and grows rapidly after grazing. It is usually lower-yielding compared to sorghum-sudan hybrids, which have the highest yield potential of any of the summer annuals. Sorghum-sudangrasses can be used for grazing or silage, but are difficult to dry to moisture levels suitable for hay production.
Precautions. Be aware that both millet and sorghum-sudan plants can accumulate nitrates during drought conditions, so test hay before feeding and graze pastures cautiously. Nitrates will persist in forages cut for hay. In addition to grazing or hay production, these crops can be harvested as green chop, which requires the same precautions as grazing to prevent prussic acid and nitrate poisoning.
If summer precipitation limits or prevents hay production, winter annuals are the next option.
Vanessa A. Corriher is a Texas AgriLife Extension forage specialist located in Overton, Texas.