High temperatures and sustained drought, especially in the extreme southern part of the state, have resulted in severe damage to many cornfields, which now are unlikely to produce economic grain yields.
University of Illinois extension educator Robert Bellm reminded producers wanting to salvage this drought-damaged corn for livestock feed to do so very carefully because there may be high nitrate levels in the forage.
“These levels will be highest in fields that received high nitrogen fertilizer or manure applications and in plants that are severely stunted and did not form an ear,” he said.
Nitrate concentrations are highest in the lower third of the stalk. Harvesting or grazing only the upper two-thirds of the plant will greatly reduce the potential for nitrate toxicity.
Forages containing high levels of nitrate may still be safely fed if they are diluted with grain or other feedstuffs that are low in nitrate. “Within limits, animals can be conditioned to consume high-nitrate forages as long as they are introduced to them slowly,” Bellm said.
Drought-damaged corn that is going to be green-chopped and fed should be tested prior to harvest. “Animals should be limit-fed and introduced to the forage slowly,” advised Bellm.
“Making hay from drought-damaged corn will NOT reduce nitrate levels,” he added. “Hay made from drought-damaged corn should be tested prior to feeding.”
Ensiling the forage can reduce nitrate levels by 30 to 60 percent. Because fermentation may take up to 21 days, silage should not be fed for at least 3 weeks after being put into the silo or bag.
“Care should be taken when ensiling high-nitrate forages because of the potential for production of nitrogen oxide silo gases, which are toxic,” Bellm warned.
Because of the variability of nitrate reduction during the ensiling process, silage made from high-nitrate forages should still be tested prior to feeding. Recommended safe feeding levels vary from state to state and are usually given as a range.
Laboratories may report results on a dry matter basis, or “as is” moisture. Test levels based upon “as is” moisture will always be higher when converted to a 100-percent dry-matter basis. Make the conversion for the sake of consistency.
Finally, some areas of the state received scattered rainfall this week. Harvesting drought-damaged forage should be delayed at least five days following a rain event. Immediately after rainfall, there is a rapid uptake of nitrate by the plants. Waiting a few days will allow them to metabolize the nitrate and reduce the nitrate concentrations within the plant.