Rethink strategies for preventing hay fires if you’re shifting to large square bales.

Large squares offer efficiency gains and improve marketing prospects. But they’re more susceptible to spontaneous heating than small bales made at the same moisture, says Glenn Shewmaker, forage specialist with University of Idaho Extension.

That’s largely because they have a reduced surface area per unit of forage dry matter and greater bale density, he says. Density in 4 x 4 x 8’ bales is 14-16 lbs/cu ft compared to 8-11 lbs/cu ft in small squares and 10-13 lbs/cu ft in round bales.

Hay fires usually occur within six weeks of baling, but can also start in cured hay as external moisture is added or more oxygen is allowed inside a stack. As a guideline, don’t let moisture contents exceed 18-22% in small squares, 14-18% in large rounds and 14-16% in large square bales.

“Those aren’t absolute numbers, because a variety of other factors, such as plant maturity, forage type and weather differences, can contribute to spontaneous heating,” says Shewmaker.

Keep a journal of weather conditions at key points during harvest to help head off fires, he suggests. Record dates and drying conditions at cutting, raking, tedding, inversion and baling.

“A journal is part of a process that will keep moisture levels on your radar screen,” he says. “From a legal standpoint, it will give you a good record of the steps you took to keep a fire from happening.”

Once you start baling, use a hand-held, electronic moisture probe to test the first three bales from each field. Shewmaker advises probing in two places on the sides and ends of each bale, totaling 12 readings.

“That will give you a pretty good idea of what the average moisture is throughout the bale. If it’s lower than the guideline for the type of bale and type of forage you’re working with, you can go ahead and bale.”

Keep a close eye on the baler moisture meter or the bale pressure indicator as you continue to bale. When you spot a change, stop and re-test additional bales.

Before stacking bales, mark the ones with higher-than-desired moisture. Separate those from dry bales and leave spaces between them to facilitate air movement and drying. Don’t store high-moisture bales in a large stack or barn. If possible, get those bales fed as soon as possible.

If moisture is marginal, limit the stack to a single column with no more than 500 tons/stack and allow at least 100’ of separation between stacks. Monitor a stack’s moisture and temperature at 20 locations at least twice a day.

“You don’t necessarily have to get into the center of the bales with the probe to test,” Shewmaker says. “Instead, aim to get to a depth of at least 3', because that’s where the heat and moisture that can cause a fire will accumulate.”

As a backup, send three composite-core bale samples for moisture testing and forage-quality analysis to a lab certified with the National Forage Testing Association (NFTA), he suggests.

“Lab testing will verify that the moisture readings you’re getting from the handheld probe are accurate. You don’t want to rely on any one thing to determine moisture levels and the potential for heating. Use all the tools that are available to you.”

For another perspective on hay fires, check out this recent post on University of California Extension’s Alfalfa And Forage News Blog.

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