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Pre-harvest precautions help minimize risk of silage gas

You put up silage to help your cattle stay healthy and well-fed. You don’t put up silage to make a home-made version of a World War I-era gas bomb. But that’s what might happen if you’re not careful when you store your silage.

“Quality silage starts all the way back in the field — and so does overall silage safety,” says Renato Schmidt, Ph.D, technical services forage, Lallemand Animal Nutrition. “Dangerous gases can be produced naturally during the early stages of the ensiling process. The right conditions can intensify the production or releases of these gases.”

First, Schmidt recommends producers practice timely and adequate nitrogen fertilization as well as manure application, taking care to include the manure-slurry contribution in nitrogen calculations. Furthermore, producers need to be aware that crops like corn, sorghum, small grains and sudangrass are more likely to accumulate nitrates.

Next, producers should avoid harvesting during unfavorable weather conditions. Periods of droughts followed by heavy rainfall — as well as damage from frost and hail — can lead to increased nitrate uptake by the plants and that can lead to production of an orange, toxic silage gas. Thus, a four- to five-day wait period is recommended.

Soon after ensiling, nitrates in the plant can be converted into nitric oxide, which and becomes hazardous when it combines with oxygen in the atmosphere to form toxic nitrogen dioxide (NO2). When continued oxidization occurs, dinitrogen pentoxide (N205) is produced. Schmidt warns this is a highly unstable compound that forms nitric acid when it reacts with water. The decomposition of N205 results in nitrogen dioxide, which is dangerous to famers if even small amounts are inhaled. Nitrogen dioxide can lead to pneumonia-like symptoms and death if not recognized and treated properly. Even brief exposure can be fatal.

Even if producers harvest forages correctly, it’s still important to take common-sense safety measures after ensiling. Schmidt recommends avoiding entering the silo during the first three days after filling. If it’s necessary to enter the silo, ventilate the area first and always enter with another person. If possible, use a self-contained breathing apparatus.

Warning signs of dangerous gases include a yellow or brownish color and a bleach-like odor. The gas can leave yellow or orange stains in the silage or on other materials. Even if no signs are present, don’t let children near silos. Producers can also post signage to warn people of the dangers of silage gas.

“Even a natural byproduct of the ensiling process can be dangerous when not properly recognized and handled correctly,” Schmidt says. “Silage safety begins long before fermentation is complete. Producers should take precautions to prevent dangerous gases before and during harvest.”

Detailed information on silage gas and full safety instructions can be found within technical bulletins, on-line university websites, and by Extension offices or available at