Bruce Anderson, University of Nebraska-Lincoln forage specialist, says to be aware of nitrates in corn stalks. Rumors, he says, are circulating that, after a freeze, the nitrates will leave the stalk. Thus, it should be safe to bale or graze corn stalks after it freezes even if the stalks currently contain high nitrates.
"In real life, though, a freeze probably will have no effect at all on nitrate levels," Anderson warns. "Almost all our corn plants will be mature and dead before it freezes this fall. And if some plants are still green and alive, a freeze might actually cause a brief increase in nitrate levels."
Some people believe it will be safe to graze stalks after grain harvest. In most situations that's correct. But not all the time, he adds "Nitrates do tend to decline as plants mature, and plants that produce grain tend to have lower nitrate concentrations," he says. "Also, the husks and leaves that cattle prefer only rarely have high nitrate concentrations.
"But notice that I didn't say always. I used the words tend and rarely. This has been a stressful year. Dryland fields still may have high nitrates, especially in that lower stalk. You may be tempted to force animals to graze stalks a bit harder than usual this year. Cattle may start out selecting safe husks and leaves, but as that supply declines they will graze more of the lower stalks with potentially dangerous nitrate concentrations.
Anderson says to pay it safe. "Before grazing, sample your stalks. Check nitrates in the lower foot of stalk. Check nitrates in the upper portion along with leaves and husks. What you discover could save your animals' lives," he says.