The rainy weather this spring has made harvesting and drying hay for safe storage more difficult, potentially raising the risk of barn fires, a Purdue Extension forage specialist said.
Storing hay with a moisture content of more than 20% without using a preservative could allow the growth of bacteria that release heat and cause mold formation, said Keith Johnson, professor of agronomy. This process increases the inner temperature of the bales, sometimes high enough to cause spontaneous combustion.
Johnson said it can take three to four weeks for temperatures to reach critical levels. He advised farmers to check stored hay regularly for warning signs of moisture or heating, including checking the temperature within stored bales and touching bales to see if they are hot.
Farmers should also be alert for steam rising from bales, condensation on the walls or ceiling of the barn, mold on the outer surface of the hay or an acrid odor. Hay temperature probes are commercially available.
If the internal temperature of a bale or stack is around 150 degrees, farmers should move the hay to allow air to circulate while continuing to monitor the temperature. If the temperature exceeds 175 degrees, fire may be imminent, and the fire department should be called.
Smoldering hay can ignite and burn rapidly when exposed to air, so if fire is suspected, farmers should not attempt to move the hay themselves, Johnson said.
To help forage dry faster when cut, farmers can lay it in a wide swath with a mower-conditioner, Johnson said. This exposes the hay to more sunlight and helps it dry faster. Additionally, the mower-conditioner crimps the stems of the hay, allowing moisture to escape more quickly. With more difficult drying conditions, farmers can consider tedding or windrow inversion.
Farmers may also let the cut forage wilt to 50% moisture content, then ferment to silage, Johnson said. This is done by wrapping the hay in white plastic using an individual bale wrapper or in-line tuber, both of which keep air out and allow lactic acid-forming bacteria to ferment the forage.
The resulting low pH keeps the forage in a stable condition during storage. This process reduces drying time but involves additional packaging costs.
Farmers interested in learning more about hay combustion can find additional resources in the Purdue Extension Forage Field Guide, available from the Purdue Extension Education Store at https://www.edustore.purdue.edu/item.asp?Item_Number=ID-317.