May 23, 2007 | By: Laura Skillman

Producing hay in the springtime in Kentucky can often be challenging at best, as farmers struggle to produce quality bales between showers. After all the hard work, producers don’t want to let the excessive heat within bales result in them going up in smoke.

Every year in Kentucky, hay bales catch fire because of excessive heating. This sometimes leads to large losses of closely stored bales, as well as perhaps a storage building. There are some steps farmers can take to avoid excessive heating in hay bales.

“Moisture is generally the culprit to hay heating,” said Tom Keene, University of Kentucky College of Agriculture hay marketing specialist. “The two moisture levels that need to be monitored are at the point of baling and when the hay is put into storage.”

Research shows that for small bales, the moisture content should be between 18 and 20 percent while for large round bales it should be between 15 to 18 percent. Even if hay is baled at these moisture levels, it can still excessively heat sometimes, especially if incorrectly stored.

The most reliable way to check for moisture in hay is with a microwave oven, which takes about 20 minutes. Farmers may obtain instructions on the full process through the UK Cooperative Extension Service. Commercial moisture meters are also available and do a good job. Some meters also come with a temperature reading. If moisture levels are too high, put off baling until hay reaches desirable levels. Preservatives can allow for baling at high moisture levels, but be sure to read and follow label directions.

Hay generally goes through a heating cycle after it is baled, so it is best to let large round hay bales sit for a couple of weeks before moving it to the storage location, Keene said. 

To facilitate proper curing, store small square bales on edge with the cut side up. This will allow warm, moist air to escape the bale better. Round bakes or midsized square bales should be left outside until temperatures have approached ambient temperature. 

After baling, check the temperatures within the bale. It is not unusual for internal temperatures to be 100 degrees and may go as high as 130 to 140 degrees. As they temperature increases so does the risk of fire. If you see it climbing above 130 degrees, check it 
on a daily basis. Check it several times a day if the temperature continues to climb, Keene said. If it is in a storage structure or in a tight row of bales outside, begin to think about moving them.

Immediately move the bales if the temperature reaches 150 degrees, and if it is above 160 and climbing, call the fire department before moving the bales.

“At these high temperatures, an influx of oxygen can ignite a fire and then it is too late to call the fire department for fire prevention,” he said. “Instead, you will be calling them to put out the fire that is engulfing your hay and storage structure.”

When building a hay storage structure, be sure to have adequate ventilation to allow for proper hay curing. As hay cures, it emits warm, moist air that rises and needs an escape route at the top of the building. If it does not escape, it condenses and falls back onto the hay which can result in the hay deteriorating and contribute to the risk of fire. Farmers may also find information on hay structures through the UK Cooperative Extension Service.


Tom Keene, 859-257-3144