Producers salvaging drought-damaged corn for livestock feed need to do so carefully because of the potential for nitrate toxicity, warns Robert Bellm, crop systems educator with University of Illinois Extension.
Nitrate levels will be highest in fields receiving high nitrogen fertilizer or manure applications and in severely stunted plants that didn’t form ears.
He suggests harvesting or grazing only the upper two-thirds of the plants; the lower third carries the highest concentrations of nitrates.
“Forages with high levels of nitrates can be safely fed if diluted with grain or other feedstuffs low in nitrate,” Bellm says. “Within limits, animals can be conditioned to consume high-nitrate forages as long as they are introduced to them slowly, allowing them to acclimate to the high nitrate levels.”
Before harvesting drought-damaged corn as greenchop or hay, have its nitrate levels tested. Making hay from the damaged crop won’t reduce its nitrate levels, and that hay should be tested before being fed.
Ensiling the forage could reduce nitrate levels by 30-60%. But don’t feed the silage until it has fermented for up to 21 days. Also be careful during ensiling, because the droughty corn can produce toxic nitrogen oxide silo gases. Test high-nitrate silage before it’s fed, too, Bellm says. Recommended safe feeding levels, which may vary from state to state, are usually given as a range.
Finally, don’t harvest drought-damaged forages until at least five days after rain, Bellm says. “Immediately after rainfall, there is a rapid uptake of nitrate by the plants. Waiting a few days will let plants metabolize the nitrate, reducing the concentration.”