How Dense Is Your Silage Pile?
Depending on where you are in the country, you’ve either finished first-crop alfalfa or are getting ready to start cutting. Much of the alfalfa gets harvested as haylage and put into bunkers or piles.
It’s well known that the forage in those bunkers and piles needs to be packed tightly. There are two reasons why density is important, according to Brian Holmes, emeritus professor in farmstead engineering at the University of Wisconsin.
- Porosity: Forages that are more porous allows for more air to move into the forage, which increases the amount of spoilage. Density and dry matter determine the porosity of the haylage.
- Capacity: The higher the density, the larger the capacity of the storage.
A packing density spreadsheet has been developed by Holmes and other forage specialists at the University of Wisconsin. Ideal density for piles and bunkers is 44 pounds per cubic foot or greater, or 15 pounds per cubic foot on a dry matter basis.
If you’re not hitting these density goals, Holmes suggests the following:
- Reduce the delivery rate of forage to the bunker to improve packing time per ton.
- Increase dry matter content by allowing longer crop field drying time
- Increase depth of forage
- Increase average tractor weight by adding more weight to each tractor or replacing existing tractors with heavier tractors.
- Add more and heavier packing tractors.
- Reduce packing layer thickness
- Pack for additional time
“Items 1 through 3 are somewhat difficult to accomplish if the harvest rate and bunker silo are currently being pushed to the limit. Few will be willing to slow harvest rate so packing can be accomplished, and fermentation occurs best in the range of 30 to 40% dry matter,” Holmes says. “Producers achieving high packing density have adopted the use of very heavy tractors and are using a shallow packing layer thickness. In a well packed bunker, tractor tires will pass over the entire packing layer surface at least once.”