It is estimated that about 3% of the U.S. corn crop experienced drought conditions this year, and if plants were stressed in the field, there will likely be challenges with ensiling and feeding it, according to Lallemand Animal Nutrition.
“First off, nitrates can accumulate when corn is under drought stress, and high levels of nitrates can be harmful to animal health,” said Dr. Renato Schmidt, technical services-forage with Lallemand Animal Nutrition. “We can still produce good silage from drought-stressed corn, as long as the crop is harvested correctly, ensiled well and carefully stored.”
Don’t take high-nitrate corn lightly, Schmidt warned. Even subclinical nitrate toxicity can result in decreased intake, weight gain, production and conception rates, embryonic death and, occasionally, abortions.
Nitrates accumulate in the bottom third of the plant. Therefore, producers should cut drought-stressed corn silage crops higher on the stalk. Assess the degree of drought stress in the field. Then, harvest based on a half to two-thirds milk line and whole-plant dry matter of 32-38% if ear and kernel development appear normal — at least 80% of normal bushel yields. If yield is reduced severely, then harvest based solely on the whole-plant dry matter target value, Schmidt said.
Next, drought-stressed corn tends to have low levels of lactic acid bacteria (LAB), which are essential for driving the initial fermentation process. These crops also tend to have higher levels of yeasts and molds and so tend to have more aerobically stability issues. A proven combination silage inoculant can help address both challenges, Schmidt said.
The ensiling process itself can reduce nitrates by 50-70%, he noted, but it’s important to give ensiling time to work.
“Never feed freshly chopped forage coming from a drought-stressed field,” he said. “It’s important to let forage ensile for at least three to four weeks. Then, introduce it gradually into the ration.”
Testing nitrate levels prior to feeding it to animals helps avoid toxicity. Silage can be incorporated at varying amounts depending on the results, but levels of 1.5% or greater should not be fed.
“Most important when harvesting drought-stressed forage is considering your own safety. Be cautious when unloading silage made from corn with high-nitrate levels,” Schmidt warned. “Nitrogen oxide gasses produced early during ensiling are lethal to both animals and humans.”
Schmidt noted that these gasses are typically a concern only during the first few days of ensiling and tend to accumulate in low areas since they are heavier than air. The gas can be colorless or look reddish-brown. To dissipate the gasses, run the blower for 15-20 minutes before entering an upright silo, and use caution around vents in silo bags. Workers should wear a respirator -- especially when entering an upright silo -- to guard against these gases and also prevent asphyxiation due carbon dioxide, the most common silage gas.