Determining proper moisture levels in baled hay
Plants that are cut and baled for hay tend to lose some of their vitamins and protein if they become too mature or dry. The challenge in making hay is to cut it at proper stage of maturity (while plants are still green enough to retain most of their food value) and bale it at the proper stage of dryness. The trick is to retain as much of the nutrient value as possible, without having so much moisture in the plants that the hay will mold and spoil (or heat so much after baling that it triggers spontaneous combustion and burns up a haystack).
There can be quite a variation in “safe” or “desirable” hay moisture, depending on conditions. It’s really difficult to make specific recommendations, since a specific figure might be too dry in some situations, and too wet in others. It depends in part upon the type of hay (alfalfa or grass – and the type of grass), the maturity of the hay when cut, the dryness of the hay when baled, whether the bales are small or large (big round bales, large square bales, etc.), weather conditions (air moisture, ground moisture), whether hay is baled soon after being cut or several days late, and so on.
In some situations, eight to 15 percent moisture is much too dry; the leaf quality will be lost. Leaves will shatter when the hay is baled, and much of the leaf material will not end up in the bale (especially in small bales – you’ll end up with stemmy hay and few leaves). The leaves contain most of the protein and nutrition, so if leaves are lost, the hay quality will be very low.
Some types of grass hay, in dry weather conditions or on dry ground, will be much too dry when baled as small bales using the eight to 15 percent moisture (the traditional rule of thumb) as a guide. Some of this grass hay produces the best quality bales when baled at 24 to 30 percent moisture. This figure refers to external moisture, not stem moisture (the plant should have little or no stem moisture) and only applies to small bales. At the other extreme, when using large bales, with some types of hay, you have to very careful baling anything over 15 percent moisture; even 18 percent may be much too high. The mass per square inch is so much greater in the big bales, and also there is less surface area for continued drying.
A key factor in when to bale hay is stem moisture, according to Michael Thomas, a rancher near Salmon, ID who also does custom hay harvesting. “If stem moisture in a certain cutting is low, then 24 percent overall moisture in the hay is not a problem – when making small bales,” he says. “For large round bales or big square bales, the percent must be much lower.”
If stem moisture is high, a professional hay producer will halt the baling when moisture content gets up to 18 percent, or even less for big bales. To make good hay, enough moisture must be present to keep all the leaves intact. Too dry, and they shatter and fall off during the baling process. Too wet, and hay will heat and mold.