By PR Extension Office
The race to beat the grasshoppers and alfalfa weevil has been especially challenging the last few weeks due to the almost daily thunderstorms. How devastating it is to see a beautiful field hammered by hail, reduced to sticks in the field; blown down, drowning in the field; windrows blown or washed away, or floating on water…all of which have been witnessed in the last three weeks, according to MSU Powder River Extension Agent Mary Rumph.
Moisture is a critical consideration in quality bales. Too much moisture causes browning- which can trigger heating and combustion. It can also cause molding, which consumes nutrients in forage and creates toxins and spores that cause animal health problems. As bales get bigger, denser and heavier, moisture percentage needs to be lower. For example, a small square bale weighing 60 pounds can be put up around 18 percent, whereas a 4-foot by 4-foot bale weighing 2,500 pounds should be closer to 14 percent. As a general rule, MSU Extension recommends always baling below 20 percent moisture and above 12 percent. Some local producers report baling large round bales up to 25% moisture readings successfully.
Problems following heating and water damage of hay include decreased quality, increased waste, and molding. Generally, the larger and more dense the bale of hay, the greater chance for heating and storage losses. Large round bales and large square bales are more susceptible than small square bales to losses and spontaneous combustion.
“The first challenge is getting the hay cut, baled and off the field. The second challenge is to keep it from going up in smoke,” said Rumph. Rained on hay can cause increases in the internal temperature of the bale, which can then lead to spontaneous combustion. An Oregon report stated that the bottom bales of large stacks of hay stored outside had soaked up a large amount of moisture from the ground after a heavy rain, causing heating and internal combustion in the hay stack.
Spontaneous hay fires usually occur within six weeks of baling and more frequently in grain hay. When external moisture such as heavy rain is added, issues can arise outside of that six week timeframe. Increases in bale moisture increase microbial activity, with heat as a by-product. It is typical to see temperatures peaking 3 to 7 days post-rainfall, but should return to normal by 60 days. This will depend on factors such as relative humidity, bale density, and amount of rainfall received. The longer it takes for the bale temperature to return to normal the more likely for a fire or significant damage will occur to the hay.
When available, a bale thermometer will be the most accurate estimate of internal bale temperature. Ensure that the thermometer can read up to 200 degrees fahrenheit and is long enough to reach the middle of the bale. If a thermometer is not available, an easy way to test the temperature of your bale is to stick a crowbar or a metal rod into the middle of the bale and keep it there for approximately 10 minutes. When the crowbar is removed, it should cool to the touch. If it is warm to the touch, then it is an indication of internal heating and should be taken care of immediately. If the crowbar is too hot to touch, this indicates that spontaneous combustion could be imminent. All stacked bales should be spread out, to allow for as much air movement through and around the bale as possible.
Perhaps a more well-known and more likely effect of rained-on hay is molding. In a standing crop of forage, the plant surfaces are covered with bacteria to help protect the plant against external assaults such as fungal infections, yeast, and potentially visible light. Once cut, the forage moisture begins to decrease, altering the bacterial populations and potentially increasing fungal and yeast populations. In normal moisture hay (<15 % moisture), fungi will not grow well and there are usually limited mold issues. However, when the bale moisture is increased, this opens the opportunity for fungal and mold growth.
Cereal hays are especially prone to molding and heating issues. At harvest, the stems of the plant are sufficiently dry, however the moisture in the grains is still above desirable levels. The grain loses moisture at lower rates than the rest of the plant, and at baling moisture percentages are often above 15%. Mold is commonly seen in these areas first, which then can spread to the rest of the bale.
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