Forage ash content comes from both internal and external sources. Internal sources include minerals such as calcium, phosphorus and potassium found in the leaves and stems of forage plants. External sources include things like soil, bedding, and sand that are deposited on the surface of the forage. An average internal ash content for alfalfa is around 8% and for grass forages around 6%. Values above that represent external sources and are negatively associated with forage quality and animal performance because ash takes the place of nutrients on approximately a 1 to 1 basis. A good goal to shoot for is an ash content of 3% coming from external sources, so an ash content of around 11% for alfalfa and 9% for grass forages.
Forage harvest practices increase the external component of forage ash content. There are some management practices that growers can use to minimize the increase in ash percentage. The following list comes from a document written by Dan Undersander, Extension Forage Specialist at the University of Wisconsin:
- Raise the cutter bar of a disc mower: The lower the cut, the more likely it is to bring soil into the forage. Consider an alfalfa cutting height of 3 inches and 4 inches for alfalfa-grass mixes.
- Use flat knives on the disc mower. Angled knives create some suction and while they help to pick up lodged forage, they pick up more soil as well.
- Keep windrow off the ground. Placing a wide swath on to a higher stubble will decrease the amount of soil that can accumulate on the bottom of a windrow.
- Keep rake tines from touching the ground. Raising a cloud of dust when raking likely is adding 1 to 2% ash content to the hay.
- Use a windrow merger. Because hay is not rolled across the ground, there can be 1 to 2% less ash in the forage.