Why Summer Annuals?
- Rapid growth during the hot, humid weather
- Fills the “summer slump” of cool-season perennials
- Higher quality than perennials during the summer
- Crop rotation
- Pasture renovation tool
- A break for cattle grazing KY-31 fescue
- Rotation allows for rest and protection of perennial grasses
What to Expect
When managed properly, summer annuals can produce substantial, high quality forage in the span of 90-120 days. This is often harvested in 1-4 substantial cuts or grazings of high energy forage. Time to first harvest for multicut annuals is generally 45-60 days, depending on weather conditions. As long as enough residual is left behind, subsequent growth will be ready to harvest more quickly, with that window tightening to 30-45 days. This rapid growth will require aggressive harvesting to prevent the stand from getting rank or low quality. For ideal growth and nutrient density, nitrogen fertilizer can be added after emergence and, if needed, between each harvest.
Warm Season Annual Grasses
Single cut: Forage sorghum, grain sorghum
Multicut: Sudangrass, sorghum-sudan, improved millet, teff, improved crabgrass
Warm Season Legumes
Single cut: Cowpeas, forage soybean, Sunnhemp
Multicut: Lespedeza
Broadleaves and Beyond
Single cut: Buckwheat, sunflowers
Multicut: Brassicas, multi-species mixes
What to Know
Planting
Prior to planting, terminate the existing stand of pasture. Although some pastures may seem thin or uncompetitive, they often provide too much competition for summer annuals to thrive. Take the time to terminate existing grasses prior to seeding to set yourself up for success. Always make seeding adjustments with the weather. Temperature and moisture considerations are key for summer annual success. Most summer annuals need 65 degree soil temperatures in order to germinate. Planting into moisture is highly encouraged, especially when working with smaller seeds like millet or crabgrass that require shallow seeding depth. Correct seeding depth for seed size can make or break the crop.
Fertilization
- Refer to the most recent soil test for phosphorous, potassium, and micronutrient recommendations
- Apply nitrogen after emergence for best success
- Application rates of 40-70l bs/A of nitrogen between harvests will maximize quality and yield
Harvest Timing
Depending on species and use (cover crop or forage for various classes of livestock), most should be taken fairly early in their growth, prior to or at boot stage. This will maximize quality and prevent stands from getting “rank”, or low quality.
Grazing
Rotational or strip grazing is the most cost effective way to manage summer annual forage. Sudangrass and millet have the best regrowth, but sorghum-sudan and even forage sorghums can be grazed. Crabgrass is also an excellent summer pasture crop that readily reseeds itself and volunteers the following year. Diverse mixtures like Ray’s Crazy Mix or Summer Feast are also popular for grazing while increasing soil health.
Concerns
Prussic acid is a concern with sorghum and sudangrass products, but not millets. Never harvest and feed immediately after a frost or big rain event following a droughty period. 18 inches of growth is the preferred minimum height for grazing. If you harvest for ensilage immediately after a frost, allow 30 days for a full fermentation process and for cyanide to “gas off” before feeding. Nitrate poisoning can also occur with all summer annuals. Typically, this occurs from excessive nitrogen fertilization or untimely nitrogen fertilization. Consumption of heavy nitrate concentrations can cause death within 24 hours in extreme cases, so forages should be tested for nitrates prior to being fed.
The Importance of BMR
BMR (Brown Mid Rib) is a gene mutation, named by its showy brown mid rib, which reduces lignin content and improves whole plant fiber digestibility and was conventionally bred into summer annuals like corn, pearl millets, and sorghum products. BMRs do have some drawbacks, but these have been managed with better genetics and handling in the field. Lignin content can mean reduced standability, which has been addressed by breeding for dwarf structure.
Brachytic dwarf plants are shorter and leafier, so they have more leaf material in proportion to stalk tissue – a bonus for both field performance and fiber digestibility. This gene is named for the phenotypic characteristics. Plus, with more plant material per inch of height, they can rival traditional taller sorghums for yield.
Yield drag is another concern that sometimes afflicts BMR products. Our trials generally show slightly higher yields for non-BMR forage sorghums and sorghum-sudans, as well as superior and rapid regrowth. But looking closer at the nutritional data makes us question the edge these standard products truly provide.
- NDFd and TTNDFD are higher
- Each % increase in NDFd causes an average increase in milk production by 0.55lb/day
- BMR forages increase animal intake by 0.37lb/cow/day
BMR sorghum products and millets can also fit nicely into a rotation where corn would struggle. Since they need to be planted later, in warmer soil temperature, the timeline for harvesting a double crop small grain is more generous. The bonus is that the sorghums handle hotter, drier conditions that might knock corn yield back. With their lower lignin content, BMR products also generally have improved palatability, so cows eat more of the stem and leave less leaf litter on the ground. BMR is a good indicator but not a guarantee of better quality.