Almost every year, there is at least an occurrence of hail or high wind damage of crops in South Dakota (SD). Weather front in early morning of July 12th brought in high wind followed by pea size hail in some portion of Northeast SD. When crops get severely damaged by such early season adverse weather conditions and replanting of existing cash crop is too late, producers are left with very little option. One way to make a good use of these fields to grow cover crops for supplemental forages and soil health.
Cover crops can be grown as single species or a blend of several species. Blends or mixes tend to do better in terms of maintaining quality and the quantity of the forages and the timing of forage need can dictate the proportion of cover crops species that can be used in a blend. Generally, grasses, especially warm-season such as sorghum, sorghum sudangrass, and millets put 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. 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. For grazing, having at least 60% of the mix as grass species will help maintain not only tonnage and not forage quality but also the animal health. High proportion of brassica and or legume species can cause bloat in ruminants. Following grazing, the leftover residue (above and below ground) consisted of diverse plant species will help enhance over all soil health by adding living tissues in the ground, increasing soil water infiltration, sequestering carbon, boost soil biological activity and sometimes adding additional nutrients that can be utilized by subsequent cash crop.
Possible Nitrate Issues. Grasses and brassicas are known as efficient nitrogen scavengers and can contain toxic levels of nitrates. Testing representative cover crop sample from the field will provide an accurate estimation of nitrate content in the plant tissues. Allowing to graze only 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.
Soil Health. Livestock grazing is the most effective way of getting the best economic return from cover crops in a short term. This may encourage growers to over graze fields and not leave any residue. This in a long run can be detrimental to soil health.
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.
Source: David Karki, iGrow