A bunker or pile covering that's sealed correctly will minimize spoilage losses, says Richard Muck, U.S. Dairy Forage Research Center ag engineer.

His studies of SiloStop, a covering system using oxygen-barrier film, show its two-step method can substantially improve the quality of silage immediately beneath the cover – the top 6” – at 2’ from bunker walls, Muck says.

SiloStop's plastic film has an oxygen permeability that's one-twentieth that of polyethylene. It's used to cover the sidewalls of a bunker and overlap at the top. Then a top sheet covers the entire top surface and a plastic mesh tarp covers the top sheet, providing ultraviolet and animal protection. Gravel bags secure the film and tarp sides.

The system was tested on four corn and two alfalfa silage bunker silos and compared with 8-mil white plastic that covered just the bunker top using tires and tire sidewalls as a seal. Half of each bunker was covered with one of the two methods.

Core samples were taken at various depths before covering and after opening for feeding.

In five of the six trials, SiloStop improved silage quality, showing lower pH and ash content within the first 6” at 2’ from bunker walls as compared to the white polyethylene. The white plastic method showed 13 to 17 percentage points higher dry matter loss in the top 6” near walls as compared to Silostop. Little dry-matter recovery difference was found at deeper locations or in the middle of the top surfaces and pH values and ash contents were similar.

Lactate/acetate ratio was higher or tended to be higher in the top 12” under the SiloStop system at the wall and in the middle of the top surface. “This is additional evidence the SiloStop system was more effective at excluding oxygen,” Muck says.

The reason one corn silage bunker didn't show a quality improvement with SiloStop was because there was inadequate overlap between the wall sheet and top sheet of film.

“This indicates that careful management is needed for the SiloStop system to work properly,” he adds.

“Could one get much of the benefit of the SiloStop system by running white plastic down the walls and using the standard system of white plastic and tires on the top?” he questions. “I think so, but we have not done that comparison.”

The oxygen-barrier-film system's advantages:

1. The tarp and sand bags do an excellent job of holding the plastic against the crop;

2. The tarp appears to provide better animal and hail protection than plastic alone;

3. The top sheet, tarp and gravel bags go on faster than plastic fully covered with tires.

Its downsides include the expense – SiloStop is more expensive than traditional methods – and the tarps need to be reused to keep costs down.

Editor's Note: Any mentions of product names in this article do not imply endorsements by USDA-ARS.

View a short slideshow on how one dairyman covers his bunker silos.