Anyone who ignores the ash content of forage is seriously overestimating the value of that forage. While ash provides some minerals, it’s largely silica and takes the place of nutrients on almost a one-to-one basis.
Forage ash comes from internal sources, including minerals such as calcium, magnesium, potassium and phosphorus, taken up by the plant root system and transported to leaves and stems. But it also comes from dirt, bedding, sand and other particles on the forage surface.
The average internal ash content of alfalfa is about 6 to 8%, and of grasses, about 6%. Additional ash in a hay or silage sample is contamination with dirt, sand, etc. Forage samples submitted to the University of Wisconsin Soil and Forage Analysis Laboratory revealed average ash contents of 12.3% in haylage and 10.3% in hay.
Assuming the haylage is mainly alfalfa and the hay has a higher percentage of grass, forage samples are averaging about 4% ash contamination from external sources. Note that some samples tested as high as 18% ash. This means the animals consuming this forage were eating almost 1 lb of dirt in each 5 lbs of hay or silage.
Some minerals are necessary for forage growth and may be beneficial to animals eating the forage, but we want to keep ash content to a minimum. I recommend a goal of 10% or less total ash.
Here is what growers can do along each step of harvesting, storage and feed-out to minimize ash in forage:
• Avoid harvesting lodged forage. Dirt often sticks to the downed forage when wet. This can’t always be avoided, but it can be reduced by planting varieties that stand better and by harvesting early to reduce the lodging potential. Downed or flooded forage should be analyzed for ash and fed accordingly.
• Raise a disc mower’s cutterbar. Raising the cutterbar lowers ash and raises forage quality; lowering the cutterbar results in greater yield. Individuals must decide which tradeoff to take, but generally a cutting height of 3” for pure alfalfa and 4” for alfalfa-grass mixes seems best.
• Use flat knives on the disc mower. Flat knives will pick up the least ash at mowing. Several disc knife types are available, including a standard knife that comes in a 14º angle. An angled knife will create some suction to pick up more downed hay and ash when soil is dry.
• Keep windrows off the ground. Start with a wide swath and place the cut forage onto dense stubble. That eliminates a layer of soil on the bottom of windrows.
• Keep rake tines from touching the ground. This can be done if the forage is on top of the stubble and the ground is level. Wheel rakes tend to incorporate more ash because they are ground-driven. Anyone who raises a cloud of dust while raking could add 1-2% ash to the hay.
• Minimize moving hay horizontally with a rake. Move two swaths on top of a third in the middle rather than raking all to one side.
• Use a windrow merger. Since the windrow is picked up and moved horizontally by a conveyer rather than being rolled across the ground, that will result in less ash content. Merging can keep 1-2% ash from hay or silage.
• Store silage piles or tubes on concrete or asphalt. Silage can be removed with minimal dirt contamination when conditions are dry, but not when it’s wet and muddy around the pile or tube.
Some soil contamination of grass and legume hay or silage can’t be avoided. Appropriate harvesting and storage management, however, can reduce the ash content of the hay or silage. Anyone with 10% or less ash has done a good job of minimizing it in hay or silage.