Driving across the state last week to attend the NC Corn Growers Association meeting and the Blacklands Farm Managers Tour, I observed corn fields in a wide range of conditions. Some fields look fairly promising, while others are showing severe drought stress and may have limited grain yield potential. Symptoms in the drought stressed corn fields include stunted plants, with very little biomass accumulation, and ‘burnt’ leaves.
Some of the most severely affected fields appear to be those planted early into dry conditions and subsequently exposed to prolonged drought during critical stages of corn development, particularly tasseling and pollination. When drought occurs during these stages, poor pollination and kernel development can substantially reduce grain yield potential.
For producers who have determined that a field is unlikely to produce an economical grain crop, harvesting the crop for forage may be an option to recover some of its value. This may be particularly attractive for livestock operations, although drought-stressed corn can also be harvested and marketed as forage. However, several important considerations should be addressed before making the decision to harvest drought-stressed corn for silage, baleage, or hay.
Evaluate the crop before harvesting
Before deciding to harvest drought-stressed corn, evaluate the condition of the crop and its potential to produce grain. Not all drought-stressed corn should be harvested immediately.
If pollination was successful and ears contain developing kernels, allowing the crop additional time may increase grain and dry matter accumulation. On the other hand, fields with poor pollination, limited kernel development, and severe plant deterioration may have little grain yield potential and may be better candidates for forage harvest.
Producers should contact their crop insurance agent before changing the intended use or harvesting the crop.
Nitrate accumulation is a major concern
Under drought conditions, plant growth and nitrate assimilation can be reduced while nitrate remains available in the soil. When rainfall occurs and plant growth resumes - conditions we have seen in many areas of the state in mid to late July and the first week of August - plants may rapidly take up nitrate from the soil. If nitrate uptake exceeds the plant's ability to assimilate it into proteins, nitrate can accumulate in plant tissues.
Nitrate concentrations are generally highest in the lower portions of the stalk. Therefore, harvesting the crop higher above the soil surface (i.e., ~12 inches above the ground) can reduce the amount of nitrate in the harvested forage.
Nitrate is particularly concerning because ruminants convert nitrate to nitrite in the rumen. When excessive nitrate is consumed, nitrite can accumulate in the bloodstream and interfere with the blood's ability to transport oxygen. At sufficiently high concentrations, nitrate poisoning can be fatal.
For this reason, drought-stressed corn should be tested for nitrate before it is grazed or fed to livestock.
Key recommendations
Wait for a rainfall if possible - Nitrate concentrations can increase following rainfall on drought-stressed fields because plants may rapidly take up available soil nitrate. When practical, producers should wait at least three days following a substantial rainfall event before harvesting drought-stressed corn, specially when the crop has experienced prolonged drought.
Keep in mind that this does not eliminate the need for testing.
Harvest above the soil surface - Nitrate accumulates in the lower portion of the stalk. Consider cutting drought-stressed corn approximately 12 inches above the ground rather than harvesting the entire stalk.
Moisture level is very important - Conventional corn silage is generally harvested at approximately 60–70% moisture, although the appropriate target varies with the storage structure. Baleage should be substantially drier, generally around 40–55% moisture.
Drought-stressed corn may be difficult to harvest at the appropriate moisture because plants can dry down rapidly. If the crop is too dry, achieving adequate packing and fermentation can be difficult, increasing the risk of spoilage.
Harvesting for hay - Drying does not substantially reduce nitrate concentrations. If drought-stressed corn is harvested for hay, it should still be tested for nitrate before feeding. Corn intended for dry hay should generally be below about 20% moisture before baling and storage to reduce the risk of heating, mold growth, and spoilage.
Check herbicide labels - Review the labels of all herbicides applied to the crop. Follow all restrictions regarding grazing, haying, silage, and other forage uses, as well as any required pre-harvest intervals.
Following these recommendations will help you minimize the risks associated with feeding drought stressed corn forage to livestock and may help recover some of the production costs, however they do not eliminate risk. Always test your forage before feeding and ensure that the nitrate levels are below critical and are safe for feeding. If nitrate concentrations are high, consult a veterinarian, nutritionist, or Extension specialist to determine whether and how the forage can be safely incorporated into a livestock ration.
For more information about nitrate toxicity and testing, contact your local NC State Extension agent or refer to the following NC State Extension resources:
