The higher a silage’s dry matter density, the more silage can be stored in a silo or pile, the less will be lost to spoilage and the more profit a producer should be able to realize.

So said ag engineer Richard Muck, who works at the U.S. Dairy Forage Research Center operated by USDA's Agricultural Research Service in Madison, WI, during the center’s Forage Toolbox series held at World Dairy Expo last fall.

“First, in terms of what you get in a silo, say you have a density of 10 lbs of dry matter/cubic foot with a capacity of about 400 tons of silage. If you double that density, you’re going to get 20 lbs. You’re also going to be up over 800 tons in that silo. It really affects your storage costs if you can get more material in that silo.”

To prove his second point – that higher densities reduce spoilage amounts – he quoted a New York alfalfa silage study comparing dry-matter losses in 30 commercial silos. “At about 10 lbs/cu ft of dry matter, there’s about 20% loss; if you’re at 20 lbs/cu ft of dry matter, you’re going to get about 12% spoilage. That’s about eight points difference in dry matter recovery. A substantial difference in recovery,” he said. “From a producer’s standpoint, it can pay for itself.”

Adding a heavier tractor to help pack a silage pile can also prove profitable, Muck said. University of Wisconsin ag engineer Brian Holmes looked at three dry matter densities – 12, 14 and 16 lbs/cu ft and showed that increasing density by adding packing-tractor weight can be a cost savings (see table).

“If you have a low dry matter density, you’re going to have more losses and that costs you. If you are going to use a bigger tractor to produce 16 lbs dry matter/cubic foot, you’re going to have higher tractor expenses. But when you sum these columns up, you’re getting more than $2,000 extra income with the 16-lb density over this lower density,” he said.

In a 10-year-old study of more than 160 Wisconsin bunker and pile silos, Muck and Holmes looked at how higher densities were achieved. Besides tractor weight, other determining factors are how thin or thick a load is spread as it comes into a silo and how much time is spent packing per ton. From that study, they developed Excel spreadsheets calculating alfalfa and corn silage density.

Not a lot of information is needed to use the spreadsheets, Muck says. “You need to know the height of your silo, the delivery rate of the material into the silo, the dry matter content, how thinly you’re spreading your loads, the complement of vehicles you’re using to pack and how much time each of those is actually packing that material. Out of that, you get a predicted density.”

But don’t be as concerned about the actual number a spreadsheet gives, look more at the change in density as you explore options to increase it, Muck adds. To download the spreadsheets, visit www.uwex.edu/ under the Bunker and Pile Silos heading.