Burning Bale.. Watch for Wet or Green Hay


Ag Biz News Column
By: Chad Gulley
County Extension Agent–Ag/NR
Smith County

The Burning Hay Bale

It is funny how a year can change things. Last year, we were trying to get all the hay we could during a drought when forages and yields just were not there.  One problem this year is getting hay to cure properly. With thick ryegrass/clover hay cuttings this spring, wet or green hay can easily result.

Many people cut and bale hay for themselves or for others in preparation of our winter months. May through September is our typical growing season for our warm season forages and this varies from year to year as the weather permits. There are several things producers need to keep up with as they bale hay. Moisture content, maturity of the hay, and temperature of the hay all play a factor in producing quality hay. Typically, July, August, and September are our best “drying” months for hay. Hot temperatures and low humidity helps our hay to dry uniformly.

One important thing is moisture content of our hay. Many people attempt to allow hay to dry to an optimum plant moisture level of less than 20 percent before baling. If hay is too wet when baled, several things happen. Hay loses forage quality, molds, mildews, and the hay can also build up a heat and catch on fire. Hay can also spontaneously combust or quickly burst into flames.

It is not unusual for the internal temperature of a hay bale to reach 100 to 130 degrees F before beginning to cool, especially for a week or two following the baling process. When hay temperatures exceed 100 degrees F, browning of the forage will result. If internal temperatures exceed 130 degrees F, a chemical reaction releases flammable gases that can ignite at the proper high temperatures. To check internal temperatures of hay, use a hollow probe made from pipe or rigid electrical conduit. Drive the probe into the center of the bale and then lower a thermometer down the probe. Leave the temperature sensor still for 10 to 15 minutes to ensure an accurate reading. Be sure to use a spirit filled thermometer instead of a mercury thermometer in case the glass accidentally breaks and contaminates the hay. Electronic thermometers with remote sensors can also be used. Compost thermometers with long stems are ideal.

Hay that is smoldering can quickly ignite once exposed to a fresh supply of oxygen. Watch bales closely to see if smoke comes from the bales. When baling hay, allow enough time to properly dry hay. Ideal weather for curing hay is less than 50 percent relative humidity. Some producers have purchased outside thermometers that also tell relative humidity. Local weather stations on the radio, television, and computer can give relative humidity as well.

There are also several things you can do to insure your hay is properly cured at time to bale. One is to cut hay a little taller leaving long stubble. This keeps the hay directly off the ground and aids in air flow helping to cure hay faster. Another is to mechanically fluff or tedder hay. Some people also purchase cutter conditioners that aid in hay dry time. The cutter conditioner crimps or pushes out water from the forage as it is cut thus speeding dry time as well. Others cut hay later in the day once the dew is dried helping to dry hay, especially on the bottom.  In the hay business, the weather may be your best friend or worst enemy.

Internal bale temperature of hay should be monitored regularly if you suspect hay is baled to green or wet. Internal bale temperatures over 150 degrees F is the beginning of the “danger” zone. A chemical reaction occurs and generates heat at a rapid rate. Check hay temperatures daily when in this temperature range. An internal bale temperature of 160 degrees F is dangerous. If the temperature is at 175 degrees F, prepare to call the fire department. An internal bale temperature of 185 degrees F, is the combustion temperature. Hot spots and smoldering pockets are probable at this temperature. Flames are likely to develop if hay is exposed to air (oxygen). Internal bale temperature exceeding 212 degrees F is in the critical range. At this high temperature, hay will almost certainly ignite.

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