When we think of warm season annual forage crops the summer annual grasses such as pearl millet and sorghum sudan quickly come to mind. Often warm season annual forages are thought of as an emergency source of hay for their ability to produce a lot of forage quickly during periods of dry weather when other forage sources are limited. However, they are much more versatile than just providing a quick hay or silage crop.
Recently, there has been lots of interest in using cover crops in cropping systems to provide agronomic benefits such as adding soil organic material, soil cover for wind and water erosion control, increasing soil microbial diversity, and weed suppression, among others. Now producers have found that the cover-crop benefits can be maintained when cover crops are grazed by livestock, providing some direct economic benefit along with the benefits to the cropping enterprise.
Thanks to emphasis placed on cover crops and soil health, the species considered for use as forage crops during the summer has broadened beyond the traditional sorghums and millets to include diverse mixtures of legumes, grasses, and broadleaf species. Cover crops can be as simple as a single species or more complex multiple species blends including 10 to 12 species, selected for their agronomic benefits with little regard for forage production attributes.
- The species in these blends are included for their agronomic benefits, but many appear to be productive as forages and surprisingly palatable.
- There is not a lot of information on the forage and grazing characteristics of many of the components of cover-crop blends.
- The rule of thumb is to start grazing sorghums, sudangrass, and millet at around 30 inches in height and leave a residual height of 6 to 10 inches. This is also what I recommend for cover crop blends until we know better.
- Prussic acid can be an issue with any of the sudangrass or sorghum species. It can build up any time the plant has undergone a period of stress. Common plant stresses that can induce buildup include drought, frost and herbicide application. It is generally best to avoid grazing 10 - 14 days after any stress period.
- Another potential issue these forages is nitrate accumulation, which occurs when plants take up nitrogen during a period of little to no growth. This accumulation of nitrate is generally in the base of the stem of the plant. If nitrate accumulation is suspected, testing is recommended.
- Millets do not accumulate prussic acid but can accumulate nitrates.
Warm season annual grasses are productive and well adapted to the region. They are also versatile in their use supplying emergency forage in dry weather conditions, a soil cover for fallow ground, quality grazing, and erosion control. As with any forage when grazed, stocking rate greatly influences both plant and animal performance. Warm season annual grasses fit well and have their place in forage systems, but profitability of this as a stand-alone enterprise require their season long use which may interfere with planting wheat for early fall pasture.
More details on grazing cover crops can be found at http://beef.okstate.edu/ Microsoft Word - grazing cover crops 5 31 21 article for website.docx (okstate.edu)