Selecting summer annuals for your operation -

Summer annuals provide growers with a crop that produces under conditions of limited moisture, grows rapidly and provides good response to fertilizer and water.

Travis Kidd

When it comes to selecting the type of crop that is right for your farm, it’s best to think about how you intend to use it. Warm-season annuals are versatile and can be used for grazing, hay, single-cut silage, multi-cuts with regrowth or greenchop.

The most common summer annuals are forage sorghum, sorghum-sudangrass hybrids, sudangrass and pearl millet. Each of these crops has its own set of strengths and growth characteristics that require proper management for optimum production.

Growers should consider adaptation, yield potential and the needs of their operation when selecting which type of summer annual to plant.

Choosing genetics

Genetics are an important criterion for summer annual selection. Growers should look for varieties or hybrids with genetics that match their forage needs. There are a number of forage traits that can provide agronomic or nutritional benefits.

For high nutritive value, varieties or hybrids with brown midrib 6 (BMR-6) genetics perform well. For example, forage sorghum with the BMR-6 trait have 40 to 60 percent less lignin compared to conventional sorghum, and BMR-6 sorghum silage has similar – and often times better – nutritive value than corn silage.

BMR-6 sorghum produces a higher percentage of digestibility and increased palatability, supporting more cattle weight gain and increased milk production than conventional sorghum.

Another characteristic to consider when choosing your summer annual is the brachytic dwarf trait. Brachytic forages have reduced internode length without affecting other agronomic plant characteristics, such as leaf number, leaf size, maturity or yield/biomass production.

Brachytic dwarf forages typically grow to about 6 feet tall and produce comparable tonnage to taller hybrids by producing more leaves and more tillers. Sorghum with this trait has very high leaf-to-stalk ratios, prolific tillering, superior standability and comparable tonnage to normal height sorghums with little to no lodging.

The dry-stalk trait reduces crop moisture in sorghum and sudangrass. Forage sorghum hybrids with the dry-stalk trait allow growers to ensile the harvested crop at reduced moisture levels with less opportunity for spoilage.

When harvested at the soft dough stage, forage sorghums with the dry-stalk trait have approximately 64 to 69 percent moisture content.

Photoperiod-sensitive sorghums initiate flowering in response to day length. Sorghums with this trait will not initiate heading until the day length becomes less than 12 hours and 20 minutes.

Consequently, photoperiod-sensitive sorghum will remain vegetative from mid-March through September. The advantage of this trait allows the plant to remain vegetative for most of the season, adding new leaves and maintaining very high-quality forage.

This allows flexibility in timing the harvest, eliminating issues associated with weather or availability of custom harvesters. The forage quality of photoperiod-sensitive sorghum will begin to decline once the plant initiates heading and flowering.

Male sterile plants produce no anthers and thus no pollen for self-fertilization. If no pollen source is nearby to cross-pollinate, then male sterile plants will produce no grain. Levels of sugars and protein increase in the vegetative portions of the plant, generating excellent forage quality and palatability.

When combined with the BMR-6 trait, male sterile forage sorghums will have higher energy content than other hybrids that produce grain.

Forage sorghum

Best uses for forage sorghum are single-cut silage and standing greenchop production. Forage sorghums are generally taller, produce more leaves and are later-maturing than typical grain sorghum hybrids.

Many forage sorghums have a sweet stalk, making them very palatable to livestock when used for grazing or hay production. Forage sorghum can produce very high-biomass yields but generally has less regrowth potential than sudangrass or sorghum-sudangrass, which makes forage sorghum an excellent choice for single-cut silage and standing greenchop production uses. The soft dough stage is considered the optimum time for harvesting.

Sorghum-sudangrass

Best uses for sorghum-sudangrass include grazing and hay production. Sorghum-sudangrass hybrids are typically crosses between forage sorghums (female parent) and sudangrass types (male parent). They characteristically reach a height of 6 to 8 feet, have smaller stalks than forage sorghum, exhibit strong tillering and produce more tonnage than sudangrass.

They have excellent regrowth potential compared to forage sorghums but less than sudangrass. The excellent regrowth ability of sorghum-sudangrass hybrids make them well-suited for multiple harvest systems.

The term “haygrazer” is typically applied to these hybrid crosses. Although sorghum-sudangrass hybrids are primarily used for grazing and hay production, they can be used for silage.

Sudangrass

Best uses for sudangrass include grazing, hay production or cover crop. Sudangrass is a rapidly growing grass which produces good-quality forage, especially hybrids with BMR genetics. It is smaller in plant architecture, has finer stalks and produces more leaves than forage sorghum.

Compared to forage or grain sorghums, sudangrass looks more like a “grass” plant. It possesses excellent regrowth ability with very quick recovery following cutting or grazing compared to forage sorghum or sorghum-sudangrass hybrids.

Total biomass tonnage for a single harvest generally will be less than yields of forage sorghum; however, a multi-cut harvest system can produce excellent yields. Sudangrass is primarily utilized for grazing and hay production and can serve as an excellent cover crop.

Pearl millet

Best uses for pearl millet include grazing or hay production. Pearl millet is extremely leafy, grows quickly, re-grows well after grazing, yields about the same as sudangrass and has excellent drought tolerance. This tall-growing, upright annual produces several stems from a central plant. It tillers out aggressively and will recover rapidly after grazing.

Pearl millet is a great choice for warm-season pasture or hay. It should be harvested in the boot stage for maximum digestibility.

Grazing and harvesting best practices

Cattle can begin grazing conventional sorghum-sudangrass and sudangrass at approximately 24 inches of growth Grazing should be stopped when the height is reduced to 6 inches to promote rapid regrowth from the remaining basal nodes.

In sorghum-sudangrass and sudangrass with the brachytic dwarf trait, grazing can begin at 18 inches and should be stopped at 4 inches.

It is recommended to leave at least two leaf internodes below the cutting when chopping sorghum-sudangrass and sudangrass for regrowth. The height of the remaining plant will vary depending on whether it has the brachytic dwarf trait or not.

When planning to make multiple cuttings, the rule of thumb is to wait for 40 days or 40 inches of growth for the highest overall season yield and highest quality. Subsequent harvests should also take place at 40 inches for optimum tonnage.

The right choice for your operation

For many growers, summer annuals are an important component of the total forage program. Their ability to supplement perennial pastures during dry summer months with high-quality forage is of

great value.

The key to choosing the right summer annual for your operation is to determine the type most suited to your farm’s needs and then to select the best genetics. FG