Drought 2012: Rain can trigger a spike in nitrate levels in forages


drought 2012

DEFIANCE, Ohio — Drought conditions that have gripped Ohio and many parts of the Midwest could increase the potential for rising nitrate levels in forages.

That means growers and producers need to take extra care to test corn they feed their livestock to ensure that nitrate levels aren’t at levels high enough to sicken or kill the animal, said Bruce Clevenger, an OSU Extension educator and a member of Ohio State’s Agronomic Crops Team.

“Drought-stressed corn has the potential for elevated levels of nitrate in the stalks,” Clevenger said. This is a significant concern for growers and producers, considering most of Ohio except for some counties near the Kentucky, West Virginia and Pennsylvania borders is experiencing moderate drought, with some counties near the Indiana and Michigan borders experiencing severe and extreme drought, according to the most recent U.S. Drought Monitor.

Drought stress increases nitrate in forages because plants are unable to go through normal photosynthesis, Clevenger said. Under normal growing conditions, nitrate is quickly converted to nitrite, then to ammonia, and finally into plant proteins and other compounds. But when plant growth is slowed or stopped, nitrate can accumulate in the plant, he said.

Rain triggers spike

And while rainfall benefits growers and helps mitigate drought, it can actually cause nitrate levels to spike. That happens if the plants are subject to drought stress, rainfall, then return to drought stress, he said.

Ohio producers haven’t reported any livestock deaths from nitrate poisoning thus far this summer, according to a spokeswoman for the Ohio Department of Agriculture.

Test before chopping

To prevent potential livestock poisoning, producers are encouraged to test their fields before feeding any chopped corn from that field to livestock, Clevenger said.

The test can be done by collecting about eight to 12 randomly selected stalks (including the ear) from a field and sending them in to county extension offices to determine the nitrate percentage.

The test cost ranges from $16 to $20 per test.

Growers and producers with drought-stressed corn are encouraged to retest their fields if the conditions vary from dry to wet again. And they may want to avoid chopping corn after a rainfall because of the increased risks for elevated nitrate.

NW Ohio levels

OSU Extension recently sampled 64 corn plants from several farms with moderate to severe drought stress, normal to reduced nitrogen applications, and low and high harvest height in Defiance and Paulding counties. The testing found that the range of percent nitrate on a dry basis was less than 0.01 to 0.27 percent, Clevenger said.

Samples less than 0.44 percent nitrate on a dry basis is considered safe to feed under all conditions.

“The numbers in these samples were thankfully low, but we can’t assume these numbers for every field.”

Poisoning symptoms

Signs to look for in livestock that indicate possible nitrate poisoning include: blue-gray discoloration of skin and mucus membranes; difficult, rapid breathing; weakness and uncoordination; rapid heartbeat with subnormal temperature; and dark, chocolate-colored blood.

Death occurs soon after the onset of symptoms.

Can dilute

Producers who find elevated nitrate levels in their fields may be able to take steps that would allow them to still be able to use the corn for feed, Clevenger said. Hay, straw, corn silage with lower nitrate levels, and byproducts can be used to dilute the feed so nitrate levels are below the toxic level in the livestock feed ration, he said.

“Growers and producers who find that the nitrate levels of their fields are at a safe range can do a direct feeding of the chopped corn to the livestock or put the freshly chopped corn directly into a silo for fermentation and storage for use in the fall and winter and next year,” Clevenger said.

Fermentation of corn silage in a silo bunker bag can also reduce nitrate levels by a reduction of 20 to 50 percent, so growers and producers who discover elevated nitrate levels can reduce it using this method before feeding it to livestock, he said.


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