With forage supplies tight and hay high-priced due to drought in 2012, more cornstalks are being harvested to feed to cattle. In drought years, nitrate tends to accumulate in corn plants and result in higher-than-normal levels of nitrate in corn stover. Nitrate concentrations could be high enough to be harmful to cattle either grazing the stalks or being fed baled stalks.
How big of an issue is this? "It's not a major concern but it's something we need to continue to watch as we go through harvest this fall," says Dan Loy, an Iowa State University Extension beef specialist and director of the Iowa Beef Center at ISU. "We are kind of in uncharted territory. Producers had to feed some of their hay early to get cattle through summer as pastures dried up. Hay supplies will run short this winter to maintain beef cow herds and for feedlots needing a roughage source. Thus, farmers are harvesting more corn stover than usual for feed and forage for cattle."
ISU Extension specialists can use quick test for nitrate in stover
With drought-stressed corn plants, agronomists and toxicologists say if there were nitrates in that cornstalk when it was harvested, the nitrate may still remain in the stover later on. "We don't know at this time how much of an issue this is," says Loy, "but we have our ISU Extension beef specialists equipped with the quick nitrate test they were using on greenchop corn and corn silage in the summer. So we can continue to monitor the stalk situation through the fall and see if nitrate really is a problem."
Why is nitrate a concern in corn stover? If nitrate is present at high enough levels, how does it affect cattle?
When farmers fertilize the corn crop, normally that nitrogen fertilizer gets translocated to the ear to produce protein in the corn kernels. When drought limits the ability for that transfer to happen some of the nitrogen gets concentrated in the stalk in the form of nitrate.
If a nitrate problem in cornstalks shows up, keep in mind it can be managed
The good news is the nitrate concentration would be in the lower part of the stalk and if you are grazing cornstalks that lower part is the very last thing the cows consume, if they eat it at all. "So this potential nitrate problem, if you find it present, can be managed if you know what level of nitrate is present," says Loy. "You can blend this stover with non-nitrate stover or other roughage to feed. To void problems with nitrate, it's just a matter of taking some precautions and watching what transpires."