It’s well known that the growing environment can impact the quality of forage. Cool temperatures generally are favorable for improving fiber digestibility, hot temperatures will speed plant maturity, persistent precipitation will delay harvest, and rain on a wilting crop will leach out desirable nonstructural carbohydrates. Haymaking is a weather game.
Under extremely dry conditions — a common theme during 2021 — another forage quality metric deserves some special attention. That metric is ash content because more of what was once field soil may now be tucked away in hay barns and silos.
Forage ash content is effectively the sum of two primary sources. The first is the minerals that are inherent in the plant — components such as calcium, phosphorus, potassium, and magnesium. We normally regard these as essential and beneficial to both plant and livestock health. Typically, these minerals comprise about 8% of the dry weight for alfalfa and 6% for grasses.
The other component of forage ash content is external soil contamination, primarily silica. The likelihood of picking up soil between cutting and storing forages is enhanced by dry, dusty conditions.
While silica isn’t necessarily detrimental to an animal, it does take the place of more desirable energy-dense nutrients on a one-to-one basis. Ash or minerals contain no protein, calories, energy, or nutrients that cattle can ferment in their rumens.
Soil contamination also carries the risk of introducing undesirable fermentation microorganisms such as clostridium to the forage or animals.
What is too much ash?
When a wide array of both grasses and legumes are analyzed, ash content often ranges from about 5% to 18%. Values trend on the lower end of that range for grasses and dry hay samples and are generally higher for haylage. Although it’s impossible to keep all soil contamination out of harvested forage, a good maximum value to aim for is 11%, or about 3% external soil contamination in the case of alfalfa.
High forage ash content is not just aggravated by dry weather and dusty conditions. It can also elevate when soils are wet and muddy. Heavy rains have the potential to splash soil particles onto forage, especially if the forage is lodged. Factors such as rodent holes, previous flooding, and gravel roads will also contribute to higher ash values in localized field areas.
The greater attention to ash content has now led most forage laboratories to offer a neutral detergent fiber (NDF) analysis that is ash-free. This is designated as NDFom or aNDFom on the forage analysis report form.
To demonstrate the economic significance of ash, consider a ton of 100% dry matter alfalfa. There will be about 160 pounds of plant mineral in the ton of hay (2,000 pounds x 0.08). Every 1% increase in ash content above 8% equates to adding about 20 pounds of soil. As such, alfalfa with an ash content of 13% will contain 100 pounds of soil per dry matter ton.
Reduction through mitigation
Although it’s impossible to keep forage “dirt free,” there are strategies that can be implemented to minimize forage ash content. They include:
1. Raise the cutting height. Though a low cutting height offers a higher yield potential, it also results in more soil being incorporated into the forage. A cutting height of at least 3 inches for alfalfa and 4 inches for grass is a good compromise. In fact, cutting some grasses lower than 4 inches will significantly impact their ability to persist over the long term.
2. Make wide swaths. This will not only speed the drying rate, but also keep the wilting forage on top of the stubble and off the ground.
3. Use flat knives on disc mowers. These will create less suction and introduce less soil into the forage than angled knives.
4. Make sure rakes and tedders are properly adjusted. The goal is to move the forage, not the soil. This is easiest when the tines are adjusted so they don’t touch or barely touch the ground. Based on University of Minnesota research, wheel rakes tend to incorporate more ash into the soil than other rake types. The hay merger and sidebar rake resulted in the least amount of ash.
5. Rake as little as possible. Often, the crop must be raked, but use strategies that minimize hay movement over the ground. Mergers are much more effective in this regard as the hay is picked up before being moved.
6. Control rodents. In addition to the damage they do to fields and plants, their dirt mounds are easily incorporated into forage windrows.
7. Keep storage areas clean. Soil can be added at the storage and loading site as easily as in the field. Keep silage bags and silo piles on well-drained, solid surfaces.
Ash is one of those hidden anti-quality factors that can impede animal performance. As you view your 2021 forage analysis sheets, take a close look at the ash content in addition to the usual forage quality metrics. The goal is to claim membership in the Under 11% Club.