One way to make a good use of fields severely damaged by hail and other adverse weather is to grow cover crops for supplemental forages and soil health, said South Dakota State University (SDSU) Extension Agronomy Field Specialist, David Karki.
“In addition to grazing opportunities, the leftover cover crop residue of diverse plant species (above and below the soil surface) will help enhance overall soil health by adding living tissues in the ground, increasing soil water infiltration, sequestering carbon, boosting soil biological activity and sometimes adding additional nutrients that can be utilized by subsequent cash crop,” Karki said.
He explained that although growers can plant a single species of cover crop, blends or mixes tend to do better in terms of maintaining quality and the quantity of the forages.
“The timing of forage need can dictate the proportion of cover crops species that can be used in a blend,” he said.
For example, Karki explained that grasses, especially warm-season grasses such as sorghum, sorghum sudangrass and millets, put on rapid growth when planted early in the season.
Other cool-season grasses, such as wheat, oat and barley will also fare better than cool season broadleaves like brassicas and legumes, Karki said.
“Generally, cover crop blends planted before third week of July should have higher proportion of warm-season species, whereas the ones planted after third week of July or into August should have more cool-season species in the mix,” he said.
For grazing, Karki encouraged growers to plant a mix with at least 60 percent grass species, which will help maintain not only tonnage and forage quality, but also animal health.
Karki does caution that a high proportion of brassica and/or legume species can cause bloat in ruminants.
Possible nitrate issues: Grasses and brassicas are known as efficient nitrogen scavengers and can contain toxic levels of nitrates.
Testing representative cover crop samples from the field will provide an accurate estimation of nitrate content in the plant tissues.
“Allowing livestock to graze only the top half of the plants can also reduce the risk of toxicity as nitrates tend to accumulate more in the lower half of the plants,” Karki said.
Soil health: In the short term, livestock grazing is the most effective way to receive the best economic return from cover crops.
However, be careful not to overgraze. Residue should be left behind for long-term soil health benefits.
Residual herbicide: Many pre-emergence herbicides that allow fall planting of a forage cover crop have a four-month restriction interval.
If a cover crop species is not listed under plant-back restriction, then it will fall under the “other” category. Harvesting or using cover crops that are not listed on the label for grazing would pose personal risk to the producers.
However, if a producer does not intend to harvest the cover crop, the rotation interval requirement is not a legal requirement. — Lura Roti, SDSU Extension