When you're baling hay, moisture content can influence yield, quality and storability. If the hay is too dry, leaves will fall off, reducing both quality and yield. But if it's too wet, it can get moldy or overheat and catch fire. There is a narrow moisture range that results in good hay that keeps well. Hay can be baled a bit wetter if a preservative like propionic acid is applied as it's baled. To get good results from a preservative, it helps to know how the preservative works and what it can and cannot do.
Baled hay naturally contains millions of bacteria and mold fungi. These microbes produce heat as they consume hay nutrients. The duration and intensity of this heat determines the amount of damage. The heat also forces moisture out of the bale, something called "going through a sweat." Usually, hay gets dry enough that the microbes die or go dormant, but it can mold or overheat when there's too much moisture.
Preservatives will kill many of the microbes so less heat is produced, giving hay time to dry naturally, without the "sweat." As it dries, the preservative also vaporizes and disappears. If bales are stacked tightly into storage soon after baling, or producers fail to allow for natural drying, the remaining microbes eventually will produce mold and heat. Also, if rain, high humidity or other sources moisten the hay later, microbial activity can redevelop because the protection from preservatives lasts only a short time. Preservatives can help make good hay at higher moisture levels, but correct management is needed to keep that hay in good condition.
Source: University of Nebraska Crop Watch Newsletter.
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