Stunted forages from fields that had high commercial nitrogen levels or animal manures applied have the greatest risk factor according to Cole. A wide variety of plants accumulate nitrates including cool season grasses, bermudagrass, millet and certain weeds like johnsongrass, pigweed and lambsquarter are known accumulators of nitrates.
The “quick test” for nitrates is subjective. Any indication of risky nitrate levels should be followed up with a forage testing lab’s quantitative test ($10 or less) to more accurately assess the risk and feeding practices recommended for its use.
Nitrate levels are reduced from 25 to 50 percent when forages are harvested as silage or haylage whether in a silo or wrapped in plastic.
|A dry-weather, stunted corn stalk|
shows a high level of nitrates
Dilution of silage and hay with non-nitrate bearing feeds can help cattle cope with the high nitrate forage. If the high nitrate forage is to be grazed, dilution is a bit more difficult.
“The option is to limit grazing time each day based on the lab’s nitrate level results. Also, try to allow the animals to only graze the top half of the plants as the leaves will run lower in nitrate than the stems,” said Cole.
Should the forage receive a rain on it before harvest, Cole recommends waiting five or so days before cutting or grazing it because the rain may allow the plant to temporarily accumulate higher levels of nitrate.
(By David Burton, MU Extension)