Just one-fourth of 147 bunkers or piles sampled on 65 farms in a six-year south-central Pennsylvania study attained the average packing density university specialists say is needed for optional silage fermentation.

That density: Greater than 14 lbs dry matter/cu ft. Densities at 14 lbs or less can suffer bunker silo dry matter losses of as much as 17-20%, according to earlier research.

One goal of the Pennsylvania study was to determine how well growers in that area were packing silage corn. Extension educators Paul Craig, Dauphin County, and Ken Griswold and Sarah Dinh, Lancaster County, conducted the research.

“We anticipated that, by informing producers of existing silage densities and recommended packing procedures, improvement of forage quality of silages would result,” the researchers said. “In addition, knowledge gained by the investigators would enable more confident recommendations on bunker silo management.”

In the study, another 25% of the piles or bunkers tested had packing densities averaging from 13 to 14 lbs/cu ft dry matter. Half of the rest of the storage units sampled between 12 and 13 lbs/cu ft densities; the other half, less than 12 lbs.

Densities were greatest on the bottom level of bunkers or piles, at 14.5 lbs/cu ft dry matter, compared to the middle at 13.3 lbs, and the top, at 10.8 lbs. Maximum densities were located at the interior of the silage mass compared to positions along the edges. The outside-left area density average was 12.4 lbs/cu ft; the center-left, 13.4; the center-right, 13.2; and the outside-right, 12.4 lbs/cu ft.

“Optimal silage fermentation occurs in an oxygen-free environment,” the extension educators added. “More dense-packed silage provides ideal conditions for rapid oxygen depletion at the start of fermentation and minimizes the introduction of oxygen back into the silage pack during storage and feedout. Both of these benefits result in higher-quality forage and less dry matter loss.”