By: Ron F. Meyer
Don’t graze or feed drought injured crops with cattle or other ruminant livestock unless they have been tested for Nitrates. Five thousand parts per million is considered the upper safe limit for nitrate nitrogen in livestock forage.
It should be noted that the nitrates will not affect the corn grain on the ear for either sweet corn, or corn used for human consumption (corn meal, corn flakes, etc.), or livestock feeds and other corn grain products. Nitrates will concentrated in plant stems and to a lesser degree in the leaves of plants when normal growth has been stunted and grain production has been severely reduced or stopped. This situation can be caused by drought, frost, or hail damage. Finally, nitrate poisoning from forages primarily affects cattle, sheep, goats, and other ruminant animals. Crop and livestock producers should take these warnings very seriously because nitrate poisoning can kill cattle and other livestock very quickly. Nitrate concentrations can vary across small areas of a field or pasture so that forages that may be good in one area may be toxic just a few feet away. Weeds, such as pigweed, are especially prone to pick up and concentrate nitrates. For these reasons sampling for nitrate toxicities in a field or pasture is difficult. Taking samples in baled or ensiled forages using approved probes and sampling techniques are the only reliable methods for minimizing sampling errors. Keep in mind that research suggests ensiling forages reduces nitrate levels by 50%.
As a result of these conditions, Colorado State University Extension provides the following guidelines regarding harvesting and feeding drought damaged crops.
- Don’t graze crops such as corn, sunflowers, sorghum, or millet that have been abandoned due to drought or hail stress, without testing first.
- Test any of this year’s forages to be fed to livestock for nitrate levels (always recommended).
- Test livestock water sources also for nitrates because nitrate toxicity results from total daily consumption from both feed and water. Feeds that may be safe under normal conditions may cause nitrate poisoning when water levels are also moderate to high in nitrate levels.
- Use approved sampling methods for testing baled or ensiled forages. Take multiple samples from the throughout the pile.
Forages that test at moderate risk levels for nitrates can still be utilized. These forages can be mixed with lower nitrate testing feeds to where total consumption is at a safe level for nitrates. Increasing the energy content of total feed consumption with grain supplements can also reduce the nitrate risks for a forage. To be on the safe side it is advisable to consult with a nutritional consultant in making these feed adjustments.
A final piece of advice is to carefully compare the costs of labor, fuel, and equipment depreciation in harvesting forages from these drought damaged crops against their potential economic returns to the farm operation. Forages that are risky to sell or feed or have low market value may have more value left in place for helping to capture and retain moisture for the next crop.
Contact the Extension office for more information on nitrate toxicities, interpreting nitrate test levels, and the proper method for taking a forage sample. Further, many Extension offices have a quick Nitrate test on hand for forages.