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College of Food, Agricultural, and Environmental Sciences


Drought-Stressed Corn Has Increased Potential for Elevated Nitrate Levels

August 9, 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, an Ohio State University Extension expert said. 

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 Extension educator and a member of Ohio State’s Agronomic Crops Team. 

It's important that farmers take steps to make sure drought-stressed forage is safe to eat,” he said. “Drought-stressed corn has the potential for elevated levels of nitrate in the stalks.” 

Nitrate poisoning is a real concern for livestock production right now because of the ongoing drought conditions impacting growers statewide, 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 as of Aug. 7, according to the most recent U.S. Drought Monitor.  

In fact, this summer so far is on track to be one of the top five warmest summers on record statewide and in much of the Corn Belt, according to Jim Noel of the National Weather Service. 

Noel, whose weather updates are featured in the OSU Agronomics Crop Team's weekly C.O.R.N. (Crop Observation and Recommendation Network) Newsletter, said Stress Degree Days (SDD) for corn continue to track like the drought years of 1988 and 1934 with the SDDs total in Ohio at 304 through Aug. 5. 

“This is more than double the 140 (SDDs) when below-trend line yields occur,” he said. 

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.

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.

“Drought, frost, cool and cloudy weather can cause nitrate to accumulate,” Clevenger said. “And rainfall following an extended period of dry conditions may cause an immediate increase in nitrates for at least two to five days after the rainfall until the plant can convert the nitrate to protein and other plant compounds.”

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.

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.

This will help the farmer determine if the field is potentially safe for animal consumption,” he said. “At a cost of about $16 to $20 per test, this is a pretty cost-effective way to save the animals we are feeding.” 

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, he said. 

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

“Fortunately, we’ve received some recent rainfall, that, while it was not enough to erase the damage from drought, it is possible that hopefully farmers can manage  nitrate levels in some corn fields and lower the risk of nitrate toxicity to livestock.” 

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 incoordination; rapid heartbeat with subnormal temperature; and dark, chocolate-colored blood. Death occurs soon after the onset of symptoms.

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.

Tracy Turner
Bruce Clevenger