by Tamara Scully
It’s July or August, and the heat of the summer is causing once-lush pasture to dry out. Providing high quality forages during the summer months, when traditional perennial forages are slowing down, can be challenging. Add drought conditions to that, and it can seem impossible.
According to Heather Darby, University of Vermont Agronomist, who offered a webinar along with Rick Kersbergen, of the University of Maine Cooperative Extension, planting summer annuals as forage is beginning “to make a little more sense than it used to.”
Darby spoke of several different summer annual forages which have been studied. Sudangrass and sorghum, along with their crosses, several millets, teff and corn have all been researched. Sorghum is a one-cut system, with little potential for regrowth, with a height of five to eight feet or more. It isn’t the best for pasture, Darby said. Sudangrass has good regrowth potential, and can be a part of a stored feed program, as well as grazed. It is leafier, with finer stems than sorghum. The sorghum x Sudangrass crosses, particularly the BMR varieties — which are traditionally bred for high digestibility — have regrowth potential and combine the best traits of each parent. Planting is at one inch depth.
“What many of our growers have found, especially with the Sudangrass, or sorghum x Sudangrass crosses, is that successional planting of these crops seems to really work well with grazing systems,” Darby said. “When the sudangrass gets really tall, really they just go through and strip off the leaves.” Cows can’t keep up with the rapid growth of these grasses, so successional seeding helps to keep the grasses at the proper height for grazing.
“You really do need quite a lot of nitrogen for these crops,” Darby said. Manure should be applied before each seeding, and perhaps after grazing, as the nitrogen needs are similar to corn.
In a Sudangrass system, the proper grazing height is 18-30 inches, and grazing should be stopped at six-eight inches in height. Two grazings are possible per season, while three may be ‘pushing it,’ Darby said. In on-farm research, the third grazing saw significant decreases in forage availability and quality.
Kersbergen stated these grasses have the potential for HCN (Hydrogen cyanide) poisoning if used as green chop or on pasture. Waiting until the grass is 18 inches tall before grazing is one way to minimize the risk. Time and fermentation eliminate the risk when stored. Increased carbohydrate supplementation should be used, and a 20-30 percent loss of forage should be assumed. These Sudangrass x sorghum crosses should not be used for dry forage, due to potassium issues. These grasses are great competitors, and can smother summer weeds.
Japanese millet is lower-growing, with increased leaf biomass, Darby said. It is drought-tolerant, but can better withstand wet conditions than the Sudangrass hybrids. Millet should be grazed at 12 inches, and not grazed below six inches, as the plants have difficulty recovering if grazed too low, and nitrate concentration is a concern.
Millets do have better forage quality than Sudangrass or sorghum. Although the millet yield is not as high, they have a higher protein content — about 20 percent crude protein — and better fiber digestibility as well. They do not have a risk of HCN poisoning, nor does Teff, Kersbergen said. The millets do accumulate nitrates in the lower part of the stems, and grazing this low should be avoided. Nitrates can also accumulate under stress, particularly during drought or frost, or if too much nitrogen is applied, and increase the potential for nitrate toxicity. Millets can be grown in a lower pH, with a 5.5-6.5 range. Multiple grazings are possible.
Teff is a grass out of Africa, fine and leafy, and very drought tolerant. It is rapid-growing, and “does seem to be best-suited for hay production,” Darby said. Teff seeds are very small. Teff is susceptible to being pulled out of the ground by grazing animals.
Corn is being tested in grazing systems, with on-farm experiments being conducted. Corn has a very high biomass. It also grows very quickly, and can easily become too tall for the cows to graze, and prevents them from seeing the fences. Corn does graze well at two to three feet. It is a one-graze system, as there is not much regrowth potential. It also tends to be too wet to harvest for forage, Darby said.
Annuals should be planted when soil temperatures are 60-65 degrees Fahrenheit. They produce best when temperatures are above 80 degrees Fahrenheit, and are very susceptible to frost.
“These are called summer annuals for a reason,” Darby said. They can be planted June-early July in New York state and still get a good yield before cold weather hits.
There is good potential for some annuals to be used in a double-cropping system, Darby said. Planting triticale in the spring, taking one or two cuttings, and then seeding with a Sudangrass x sorghum cross in July is one possibility. Seeding triticale in the fall, to be grazed in the spring before seeding annuals is another option to consider.
Forage is the cheapest source of nutrients, Kersbergen said, so providing as much high-quality forage as possible makes sense. High dry matter intake is key.
“When we look at evaluating forages, we need to look at what is digestible in that forage from fiber components.” he said. NDF (Neutral Detergent Fiber) is a limiting factor, and it changes as the plant matures through the season. As the plants get more fibrous, the digestible fiber decreases.
High NDF means that the intake potential is increased, Kersbergen said, and results in better animal performance. Rumen fill limits the ability of the cow to eat forages. Increased digestibility means increased nutrients available for milk production.
“Get it in the cow, get it digested, and out of the cow quickly,” he said.
It is also important to match carbohydrate supplements with the type of crude protein to maximize ruminant microbial activity. Bacterial protein drives milk production, and providing enough energy for a balanced system is a key to avoiding problems.
Other issues which must be considered when choosing a forage are wet fermentation issues, which degrade the quality of stored feed and can produce toxic materials. This is a concern with Sudangrasses and hybrids. Whether a forage is conducive to round baling may also be of concern, Kersbergen said, and the ability to round bale may make Sudangrasses a better choice than corn for some dairies.
So when the hot, dry days of summer inevitably come to pass, having warm season annual forages can make lush pastures available to the herd, even on the driest, hottest days. “Summer annuals can tolerate these conditions better than our perennial cool season forages,” Darby said. “Usually the (perennial) forages are a much lower quality at this point as well.” The annuals not only can allow nutritious, high-quality pasture to be available, they can also be harvested for feed, and “fit really well into different crop rotations on your farm.”
The webinar or accompanying written material can be viewed at: www.extension.org
by Tamara Scully