Summer annual grasses are important forage crops in the Southeast and fit well in forage systems to fill in the summer forage gap in the Fescue Belt and as an emergency forage crop for dry summers or bare ground.
They also fit well in situations where perennial warm season grasses are not desired or do not fit the circumstances. Many producers use summer annuals for high tonnage and quality. In fact, the seed industry has certainly taken note of the importance of summer annuals. In the last few years, it has gotten a lot more difficult to pick a summer annual forage because of all the different species, new varieties, and limited information (not to mention the erratic seed supplies because of drought issues). It has become confusing.
What is the right species?
There are at least 10 different summer annual grasses that could be used as forage crops in Georgia. In general, these summer annuals do not make good hay crops in our environment because of their slow drying rate. A few of these species play a role as a grazing and/or silage option and are recommended for use. Those recommended species are divided into two categories: 1) pearl millet and 2) the sorghum family.
Pearl Millet originated in Africa and is the most widely planted summer annual grass in Georgia. This tall-growing, erect annual grass produces several stems from a central plant. It tillers out more aggressively and generally recovers more rapidly after grazing than those in the sorghum family. Pearl millet is generally the best choice for grazing.
Millet produces good quality grazing from June through August. If properly grazed to avoid advanced maturity stages, the range of total digestible nutrients (TDN) can be expected to be 52-58 percent, while crude protein (CP) will range from 8-11 percent. Millet planted in spring (April) should be ready for grazing 30 – 40 days after planting and should be productive for 80 – 110 days.
Most of the production will be during the first 60 days of the life of the stand. The grazing supply can be more stable over the summer by making 3-4 plantings staggered by about 2 wks each. Well-fertilized millet should carry three to four stocker cattle or two to three mature cows per acre during the first 60 days. Lower the stocking rates during the last part of the grazing season to compensate for the reduced growth rate and lower quality.
During the last 10 years, the average yield of pearl millet in the variety trials in Griffin and Tifton was approximately 9,000 and 16,000 pounds per acre. In both cases, the year-to-year variability was approximately 25 percent. Generally, pearl millet holds up better under drought stress than the other species.
Sorghum produces more tonnage
All of the summer annuals have the potential to accumulate nitrates. However, pearl millet does not have the added risk of prussic acid toxicity whereas those in the sorghum family do have that risk.
Sorghum family species that are commonly used in Georgia include forage sorghum, sudangrass, and the sorghum x sudangrass hybrids. These species are generally better choices when the crop is fated for silage (e.g., baled silage, bagged silage, bunker/pit silage, etc.), but the sudangrasses and sorghum x sudangrass hybrids can also be used for grazing.
Members of the sorghum family generally produce more tonnage than pearl millet, except during prolonged drought. The average yields over ten years with trials in Griffin and Tifton were approximately 10,200 and 16,600 pounds per acre, respectively. In both locations, the year-to-year variability was approximately 35 percent, which is substantially more variable than pearl millet and likely due to an increased susceptibility to drought.