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OSU Extension

College of Food, Agricultural, and Environmental Sciences

July 16, 2019 - 8:33am --

A lot of forage has been baled over the past week to 10 days.  Some common questions are what harvest moistures allow for safe barn storage and how high will bale temperatures get during the sweating process after baling?  There was a good article in a recent OSU Extension CORN newsletter that dealt with that topic.  I am quoting the bulk of that article to answer these questions.

“When baled at moistures over 20% mesophilic bacteria release heat-causing temperatures to rise between 130⁰F and 140⁰F. These bacteria cause the internal temperature of hay bales to escalate, and can stay warm for up to 40 days depending on the moisture content when baled. If bacteria die and the bales cool, you are in the clear but if thermophilic bacteria take over temperatures can rise to over 175⁰F.

If you are concerned that your hay or straw may be a fire risk because it was baled at a high moisture, monitor it twice a day for the first six weeks after baling or until low temperatures stabilize. Ideally, take temperatures from the center of the stack or down about 8 feet in large stacks.  A long probe thermometer is recommended, but some homemade options are available.  A ¾-inch pipe with the ends closed into a point and 3/16 inch holes drilled in the bottom 4 inches can work well, lower a thermometer on a string or the sensor wire of a thermometer into the pipe. The sensor on a long wire can works well, and once in place you can read temperatures without removing it. Leave the thermometer in the stack for 15 minutes to get an accurate reading.  Another more crude option is to stick a 3/8 pipe into the stack and pull it out twice a day.  If the pipe is too hot to hold in your hand, you are at risk for a fire. For more information on building your own temperature probe visit   Be very cautious when taking hay temperatures because hot hay can have burned out cavities.  Use planks to spread out your weight and have someone nearby in case you fall in a burned out pocket or between bales.  Using a harness and tying yourself off is a good safety option.


Critical Temperatures and Actions to Take:

Critical Temperatures and Actions to Take

If you are in the risk zone and there is machinery or livestock in the barn remove them before removing the hay.  Call the fire department when you are in the risk range.  They would much rather be present and not have to put a fire out then have to call mutual aid when your entire barn is on fire. For more information on Preventing Fires in Baled hay and straw visit-

Bale under appropriate conditions to prevent spontaneous combustion. Recommended moisture levels for safe baling of dry hay are as follows: small rectangular bales less than 20% moisture, large round bales 15-18% moisture and large rectangular bales at 13-15% moisture.  When baling high moisture hay fields, adjust the volume of the bale to be at a lower density to improve air circulation within the bale.  Hay preservatives can be applied during baling to high moisture hay. Liquid products like propionic acid inhibit the growth of bacteria. The effectiveness of preservatives is generally good up to 25% moisture, variably effective at 25-30% moisture, and no preservative is very effective above 30% moisture.  For more details on how to maximize field curing for forage harvest, see

Proper storage involves the following:

  • When stacking and storing high moisture hay, allow for more ventilation and airflow around the bales. Good airflow will help the bales return to a normal (ambient) temperature.
  • Keep bale stacks low when storing inside a barn.
  • Provide wider spacing between stacks when storing outside.
  • Keep bales protected from excess ground moisture by storing them on gravel, pallets, used tires or other mechanisms to allow air flow.”


2019 Manure Science Review

The 2019 Manure Science Review will be held in Tuscarawas County on Wednesday, August 7.  The host farm is JIMITA Holsteins located at 9877 Strasburg Bolivar Rd. NW, Strasburg OH 44680.  Sign in begins at 8:45 am.  The program starts at 9:20 am and runs until 3:00 pm.  For those interested, there is a tour of a livestock manure composting business; Bull Country Compost, located at 10316 Kohr Road NW, Dundee OH 44624 from 3:30 to 4:30 pm.  Continuing education credits are available for Certified Livestock Managers, Certified Crop Advisors, Fertilizer Recertification, and Manure Hauler/Broker.

The early registration fee (received by July 30) is $25/person.  Registration includes morning coffee and donuts, lunch, handout materials and the compost tour.  Registration after July 30 is $30/person.  Full program details, including the speakers, topics, and a mailable registration form, are available at or by calling 330-202-3533. Online registration is available through Aug. 1 at


Rory Lewandowski is an OSU Extension Agriculture & Natural Resources Educator and may be reached at 330-264-8722.

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