Fall hay harvest
Producers continue to harvest hay to replace the deficit caused by the 2012 drought. The management challenge when harvesting hay in the fall is getting the crop dry enough to safely bale with shorter days and cooler temperatures. Fall is also the time of year when the larger stemmed forages such as forage sorghum, sudangrass and sorghum-sudan crosses are harvested, and the thicker stems take more time to dry than finer stemmed crops. Hay that is baled too wet is in danger of getting hot enough to start on fire, or at the least, losing much of its feed value.
The recommended moisture content for small square bales is 20% or lower, whereas large round or rectangular bales should be made at 18% or less and some references suggest no more than 16%. Hay preservatives can allow baling at higher moisture content, but add cost to the equipment, add cost for the product, and can be corrosive. There is also a limit of how high the moisture content can be and still safely bale hay.
It is normal for temperatures to rise in freshly baled forages due to plant respiration and natural microbial activity. If forage moisture levels are too high, however, the combination of heat and moisture provide an ideal environment for excessive growth of bacteria that are naturally present on these crops. The respiration of these bacteria can cause the temperatures to rise to dangerous levels.
The moisture content of forages can be determined with either a forage moisture tester, or by using an accurate scale and a microwave oven. If using a forage moisture tester, comparing the results of several tests with the results of using the scale and microwave oven would be much safer and provide confidence in the results. This may be particularly important when determining the moisture content of large stemmed forages, as the large stems may cause erroneous readings.
To determine the moisture content of forages using a scale and microwave oven, gather and weigh a representative sample of whole plant material. Heat the forage with a cup of cool water in a microwave oven for a few minutes at a time until the weight doesn’t change. The moisture content can be determined with the formula: % moisture = (initial weight – final weight) X 100/initial weight.
Once forages are baled, it is advised to leave them scattered in the field for at least three weeks before stacking. By that time, the temperature of the hay should rise slightly and gradually return to the ambient (air) temperature. Heat can also escape from individual bales much more readily than if the bales are stacked, and if one or more bales are heating excessively, you’re not endangering the whole stack to the danger of fire.
If the moisture content was borderline or questionable at the time of baling, the temperature should be monitored, particularly before stacking. If temperatures rise to no more than 120 degrees F, no loss of feed value should occur and no action is needed. If temperatures rise to between 120-130 degrees F, some loss of feed value can be expected, and temperatures should be monitored daily. At 140 degrees F, significant feed value can be lost and one should consider taking stacks apart. If temperatures rise to 150 degrees F or higher, significant loss of feed value is certain, and fire is likely.