By: Keith VanSkike and Alyssa Rippe-May, Twin Creeks Extension District
News Release - 8/17/2022
High producing crops such as corn and sorghum tend to accumulate high nitrate levels in periods of drought, excessive heat, hail, and in other environmental stresses. All plants contain nitrate, used to create amino acids, the building blocks for proteins. However, in years of poor growing conditions when yields are expected to be low or little grain fill occurs, nitrates accumulate in the lower leaves and stalk of the plant instead. High production fields with high fertilizer application have increased potential to see this nitrate accumulation in plants.
The dry conditions we have experienced mean some failed corn and sorghum fields may be used as livestock feed. However, producers must be keenly aware of the potential for nitrate accumulation. Nitrate toxicity occurs in livestock if nitrate intake is faster than the body’s ability to break it down. This causes an accumulation of nitrite in the rumen, moving to the bloodstream, rendering the blood unable to carry oxygen throughout the body. The end result is eventual asphyxiation and death.
Toxicity is related to the total amount of nitrate in the diet (including water) and how quickly it is eaten. In general, if forages contain more than 6,000 ppm nitrate, they should be considered potentially toxic. Animals under physiological stress from sickness, hunger, lactation, or pregnancy are more susceptible to nitrate toxicity than healthy animals. See the table below for effects of various nitrate levels, reported as nitrate.
| ppm Nitrate (NO3) |
Effect on Animals |
| 0-3,000 | Virtually safe |
| 3,000-6,000 | Moderately safe in most situations; limit use for stressed animals to 50% of total ration. |
| 6,000-9,000 | Potentially toxic to cattle depending on the situation; should not be the only source of feed. |
| 9,000 and above | Dangerous to cattle and often will cause death. |
As you receive your own test results, be sure to watch how nitrates are reported. Depending on the chemistry that is reported, you may need to use a conversion factor to utilize the table above.
It is wise for producers to test their drought-stricken forages for nitrate levels. Nitrate testing can be done through a variety of good, certified labs in our area. Testing is especially important following a rain as nitrates move throughout the plant. Delaying harvest or grazing 7-14 days may be necessary to prevent toxicity. Knowing how a forage will be fed is integral to making appropriate decisions.
Baling
If swathing and baling is your plan, harvesting the forage 6 to 12 inches above the ground will avoid the highest concentrations of nitrates in the plant. Collecting a representative sample prior to harvest will help you make an accurate determination. Be sure to collect only above your planned cutting height and take samples throughout the field. Combine several samples from different areas of the field, then cut up stalks and leaves, and mix well. Only after mixing well should you remove your test sample to be sent to the lab.
If high nitrates are found, grinding and mixing with other ground hay can help dilute the nitrate concentration. Frequent feeding in limited amounts and blending gradually with other feeds can help animals slowly acclimate if levels are not too high. Supplementation of 2 to 5-pounds of grain or by-products provides energy for rumen bacteria to more quickly convert the nitrite to a usable form. Molasses can also provide needed energy for rumen microbes. Formulating rations to ensure adequate energy, protein, and particularly Vitamin A will help. Nonprotein nitrogen (urea) should not be fed with high nitrate feeds.
Silage
Ensiling is the safest way to utilize high nitrate forages. If you wish to ensile the droughted forage, silages made from stressed forages should be analyzed after ensiling as the fermentation process usually removes about 50% of nitrates. This is not the same as harvesting as hay, in which nitrate concentrations remai in the dry hay. It is still not a bad idea to leave 6 inches of stubble in the field. That is the portion of the stem with the highest concentration of nitrates. Utilize safe silage pile sampling techniques by removing silage from the pile first, then grabbing your sample from the tractor bucket. Mix several samples together to then remove your subsample for the lab.
Grazing
Grazing high nitrate forages can be a dangerous practice. Grazing pressure should be limited so that animals do not consume the parts of the plant forage testing shows to be dangerous. Although animals tend to consume the leaves and the top portions of the plant, which contain less nitrates, the risk of consuming a high-nitrate portion of the plant still exists. In addition, the longer the animal is left on a field or the shorter the plants, the more that animal is forced to eat the lower portions of the plant increasing the risk of nitrate poisoning.
For more information, see K-State Research and Extension publication MF3029, “Nitrate Toxicity”, at your local county Extension office, or at https://bookstore.ksre.ksu.edu/pubs/MF3029.pdf.
This article was adapted from “Nitrate toxicity in drought-stressed corn and sorghum”, K-State Agronomy eUpdate, Issue 917.