Summer annual pastures can provide valuable, high-quality forage during a season when your permanent pastures may be running out of gas. Almost all parts of the U.S. can add warm-season annuals as a part of their forage program. Forage crops, ranging from corn to crabgrass, fit in the summer annual category. Most cattlemen are more familiar with sudangrass, sorghum-sudan hybrids and millets as summer pasture crops.
Using cornstalk fields for wintering dry cows is a common practice, but using green, standing corn as a forage crop is a relatively new concept in the U.S.
Crabgrass may be a weed to crop farmers and hay producers, but it's a very valuable annual forage for cattlemen. Knowing where, when, and how to use these crops is the key to success.
All annual pastures, except crabgrass, are relatively expensive to establish. Thus, you need a high-value product or very efficient use to afford them. As finishing cattle on pasture and running stockers typically generate a higher net return, these are enterprises where summer annuals may be particularly valuable. Meanwhile, cow-calf operations typically experience lower returns, so summer annual use may be harder to justify.
If the annual pasture extends your grazing season and allows you to feed less hay in the dry summer or winter months, and as long as the cost per day for the annual pasture is lower than the cost of hay, it's a viable alternative.
Capturing a better return
Controlled grazing will help you capture a better return on your investment through high grazing efficiency compared to set stocking. If you're going to spend money to establish and grow annual pasture, spend a little more to manage it more effectively.
I've seen pasture yields on summer annuals as low as 50-70 AUD/acre to more than 400 AUD/acre. Some of the difference is due to additional irrigation or fertilizer, but much of it is attributable to inefficient grazing when the summer annual gets head high.
One big challenge of using summer annual pasture is its explosive growth potential in hot weather. If there's moisture, warm-season annuals can grow at astounding rates. The crop can get away from you literally overnight.
Most annuals can support much higher stocking rates than perennial pastures, so be prepared to go to the pasture with a lot of animals. Keeping the pasture under control takes aggressive management. Once warm-season annuals get taller than the animals, grazing efficiency drops significantly.
One of the first concerns for many cattlemen is the risk of prussic acid (PA) poisoning from annual pastures. Prussic acid is a precursor to cyanide and can be deadly.
Only the grasses in the sorghum family contain this toxin. Corn, millets, and crabgrass are PA-free. A low-level PA is almost always present in the sorghum family but doesn't become a problem until the plant is stressed. Drought, frost, disease or herbicide injury can lead to toxicity. Avoiding its use during stress conditions is the best preventive management.
Early in the growth stage of most sorghum crops, PA is naturally high, so don't begin grazing them until they reach a safe level. As a general rule, avoid grazing sorghums or sudan grass until they reach at least 15-18 in. height. We've all heard the neighbor's story about how he started grazing such crops at 12 in. without a problem. That's lucky for him, but don't count on the same experience.
Don't overlook crabgrass
Crabgrass is an often-overlooked forage crop. It's native in many pastures in the South and into the Midwest.
In Missouri, we found many tall fescue-dominant pastures naturally turned to crabgrass during summer months when fescue became less competitive. As much as a quarter of our annual production might come from naturally occurring crabgrass.
A few management changes can really encourage crabgrass. A shot of nitrogen in early June will stimulate the crabgrass as the fescue is fading and help summer pasture production. Resting the pasture in September to let the crabgrass set seed will ensure next year's crop. It's the lowest cost summer annual pasture available in the fescue belt.
Jim Gerrish is a grazing management consultant based in May, ID, and former lead pasture researcher at the University of Missouri's Forage Systems Research Center in Linneus. Reach him at 208/876-4067, firstname.lastname@example.org, or visit http://americangrazinglands.com.