Farm Talk

Crops

August 14, 2012

Beware of nitrate toxicity in drought-stressed corn

Parsons, Kansas — With drought stretching across the United States, plants such as corn and sorghum tend to accumulate high levels of nitrate in the lower leaves and stalk of the plant. The accumulation happens because the plant assimilation of these nitrates into amino acids is slowed by the lack of water, a crucial component to numerous plant processes, according to K-State Research and Extension crops and soils specialist, Doug Shoup.

Nitrate toxicity in livestock occurs because animals absorb the nitrates into the bloodstream where it binds to hemoglobin, rendering the hemoglobin unable to carry oxygen throughout the body. The result is eventual asphyxiation and death for the animal, said Shoup, an agronomist based in southeast Kansas.

“It is wise for producers to test their drought-stricken forage prior to harvest. Nitrate testing can be done through several labs, including the K-State Soil Testing Laboratory,” he said.

Harvesting the forage eight to 12 inches above the ground to avoid the highest concentrations of nitrate in the plant is a good practice, said Dorivar Ruiz Diaz, K-State nutrient management specialist based in Manhattan. Producers should collect a good representative forage sample above this cutting height to get an accurate determination of what the nitrate level could be.

Depending on the planned feeding method, a producer may wish to harvest different parts of the

plant, Ruiz Diaz said. If wrapping the forage into a bale and feeding it directly to livestock, he or she may want to test the lowest part of the stalk to determine the greatest risk of nitrate forage that could be ingested by the animal.

If a producer plans to grind the bale, a whole‐plant sample above what will be left in the field may be a more accurate representation of what will be eaten. If a harvested forage is high in nitrate, blending the feed with another forage such as prairie hay or brome will dilute the total nitrates in the animal’s diet and could potentially reduce the risk of poisoning.

High-nitrate forages chopped for silage and properly ensiled are a safer option for livestock feeding, Shoup said. During the ensile process, potentially 50 percent of the nitrates in the forage will be metabolized by the microbes, which can vastly reduce the risk of poisoning. It is still not a bad idea to leave six inches of stubble in the field, however. That is the portion of the stem with the highest concentration of nitrates.

Grazing high nitrate forages is a dangerous practice, Ruiz Diaz said. Although animals tend to consume the leaves and the top portions of the plant, which contain less nitrates, the risk of consuming a high-nitrate portion of the plant still exists. In addition, the longer the animal is left on a field and the more that animal is forced to eat the remaining forage at the lower portions of the plant, the greater risk of nitrate poisoning.

More information is available at county and district K-State Research and Extension offices, and in the publication MF3029, Nitrate Toxicity at http://www.ks re.ksu.edu/library/crpsl2/mf3029.pdf. To contact the K-State Soil Testing Lab, call (785) 532-7897 or see more information online at http://www.agronomy.ksu.edu/SoilTesting/.£

 

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