As any experienced hay producer knows, the moisture content (%MC) of hay needs to be strictly controlled. With too little moisture, hay becomes brittle, loses nutritional value, and is unpalatable for livestock. With too much moisture, hay can spoil while baled hay can experience thermal expansion—causing it to combust and creating a severe hazard.
Because of this, checking the moisture content of hay with a hay moisture meter before baling begins is an integral part of harvesting.
With this in mind, the question is, “What is the right amount of moisture in hay, then?” Just how dry does hay have to be before it can be baled? The answer to this question varies depending on several factors, including what kind of forage you’re using for hay, and how you’re baling it.
Small Square Hay Bales
Of the different kinds of hay bales, small square bales tend to have the highest tolerance for moisture. According to research cited by the Alberta Agriculture and Rural Development site, a small square bale’s moisture content can be between 18% and 20% and be safe.
Part of the reason for this is because small square bales tend to be much less densely packed than larger hay bales. For example, at 5.5 cubic foot of volume with a weight of 60 lbs. or less, there is less than 11 lbs. of matter per cubic foot of space in a small square hay bale (60 ÷ 5.5 = 10.9090). Compare this to a large rectangular bale, which packs 1,800 lbs. of material into 112 cubic feet of space, which means there is roughly 16 lbs of matter per cubic foot of space, again nearly half as much as the small square bale.
The biggest challenge when dealing with small square hay bales is that processing so many smaller bales is inefficient when compared to simply making one huge bale. To recall the previous example, for a small square baler to match the output of the large square baler, it has to make 30 bales, which means stopping for the baler to finish 30 times to other unit’s single stop.
Large Square Hay Bales
Being more densely packed than small square hay bales, large square bales have a much lower tolerance for moisture. For a large square hay bale, the allowable range for moisture content is often between 12% and 16% with 12 being more desirable for long-term storage and warmer climates.
With their very low moisture tolerance, large square hay bales can be much more finicky to get dry enough for storage or transport, but they do have their advantages, such as:
Using a large square baler is often faster and more convenient than using a small one.
Large square hay bales are easier to load onto flatbeds for transport than other types of hay bales.
With a higher density than small square bales, large square bales are more efficient on space per pound, and are much easier to stack and transport than round bales.
For a hay grower who is looking to deliver large quantities of hay over long distances, large square bales are often the best choice.
Round Hay Bales
Many newer baling machines render hay into barrel-shaped round bales instead of the traditional compacted square shapes. While the density at which these bales will still differ depending on overall size, the moisture tolerance of round-shaped bales holds fairly steady at 15% MC.
These bales are often easy for a single farmer to manage efficiently, but are more difficult to transport over great distances than the other two types of hay.
The Consequences of High Moisture Content in Hay Bales
When the %MC in a hay bale is too high, the hay will undergo a process called thermal expansion. To put it simply, hay bales will become hot as the moisture inside the bale attempts to bleed out.
During this process, bacteria and mold in the moisture trapped in the bale may multiply, using the nutrients in the bale to fuel their growth. In the best case scenario, this may merely strip the bale of useful nutrients and make it inedible to livestock. In a worst-case scenario, the hay will continue to become hotter from the growth of these microscopic organisms until the heat and pressure causes the bale to spontaneously combust.
The higher the moisture content of the hay, the larger the risk will be.
When hay doesn't have enough moisture
Of course, if hay’s moisture content is too low, then different problems will occur. While hay with exceptionally low moisture might not be at risk of growing mold and bacteria, that’s because much of that hay’s nutritional value is already gone.
When hay is too dry before baling, the leaves of the forage become stiff and brittle, making them much more likely to fall off. In many cases, a significant portion of hay’s nutritive value lies in the leafy portions of the herbs used to make the hay.
Verifying Moisture before Baling
Because of the incredibly challenging demands of growing top-quality hay, many farmers are up before the crack of dawn to start collecting hay so that they can get as much as possible before it becomes too dry.
Using hay moisture meters with extended-length probes, these professionals check moisture levels in the windrow before activating their balers so that they know that their hay is ready to be baled. During the baling process, many hay experts attach special baler-mounted moisture meters to their baling machines to continuously check the %MC of their hay throughout the day so that they know right away when their hay is getting too dry to continue baling.
With the right tools and a little know-how, making the best hay bales can be a cinch.