This time of year, I often get questions about what type of summer annual forages to plant in Colquitt County. Warm season annual grasses are established from seed and are productive during spring and summer. Plantings of warm season annual grasses can be made in the spring as soon as the soil temperature (at a two inch depth) warms to 65º F. Seed can be broadcast or drilled in narrow (more than 15 inches) or wide (up to 36 inches) rows. Seed should be planted at a soil depth of 1/2 to one inch. Ideally, summer annual grasses should be established on well-drained, fertile soils with good water-holding capacity. Higher seeding rates may help to decrease stem size, but it is unlikely that this will be valuable enough to compensate for the expense of the higher seeding rate. Below is a table that shows planting date and seed rate information.
New varieties of warm-season annual grasses are released periodically, so it is important to examine the yield comparison trials in UGA’s Statewide Variety Testing Program (https://www.caes.uga.edu/commodities/swvt/).
Pearl millet can be grazed or harvested as hay or silage. Growers can begin to graze pearl millet when plants reach 20 to 24 inches, but regrowth rate and animal performance is best if a nine to 12 inches stubble height is maintained. Pearl millet can make good quality hay if cut when plants reach two to three feet tall. This prevents the forage from maturing beyond the boot stage and therefore being too mature to provide high quality. The drying rate of millet hay can be sped up by the use of a roller/crimper-style conditioner.
If harvested prior to advanced maturity stages, the range of total digestible nutrients (TDN) can be expected to be 52 to 58 percent, while crude protein (CP) will range from eight to 11 percent. There is some evidence to suggest that seeding rates at the high end of the recommended ranges will promote a higher leaf:stem ratio. This may improve forage quality, but these gains may not compensate for the expense of the higher seeding rate.
Dr. Dennis Hancock (former UGA forage agronomist) conducted research looking at the effect of delayed planting on total dry matter (DM) yield and the distribution of the yield produced by pearl millet over three years in a small plot experiment at the University of Georgia’s Plant Sciences Farm located near Watkinsville, GA, from 2007 to 2009. Staggering plantings beyond late April may not improve yield distribution within the forage system because of the yield decreases associated with later plantings of pearl millet. This research article, “Late Planting Date Influences the Yield and Distribution of Pearl Millet Forage,” was published in the journal Forage and Grazingland Research in 2010.
Since pearl millet does not produce prussic acid, this species has a distinct advantage over sorghum, sudangrass, and sorghum x sudangrass hybrids. This allows pearl millets to be grazed or harvested at any growth stage and during droughts without the risks associated with prussic acid poisoning. However, pearl millets can have high nitrate levels.
Hybrids of forage sorghum and sudangrass are commonly grown as a warm season annual crop in Georgia. These hybrids have the highest yield potential of any of the summer annuals, if adequate rainfall is received or irrigation is provided. However, sorghum x sudan yields are more severely affected by drought than pearl millet, and are less tolerant of poor soil conditions and soil pH values less than 5.8. Sorghum x sudans can be used for grazing or silage, but like other annual sorghums, their forage is difficult to dry to moistures suitable for hay production.
Sorghum x sudan hybrids should be rotationally grazed, allowing the forage to reach 24 inches before grazing (i.e., managed like sudangrass). At this stage, sorghum x sudans will generally have TDN values in excess of 53 to 60 percent and CP concentrations of nine to 15 percent. Brown midrib (BMR) varieties are usually preferred varieties for grazing since they have less lignin and higher digestibility than other varieties.
Photoperiod-sensitive sorghum x sudan and forage sorghum cultivars are available. These varieties are capable of sustaining more consistent growth over a longer growing season because they remain in a vegetative stage late into September (until daylength is less than about 12 hours and 20 minutes). This trait may negate or lessen the need for staggered plantings.