If the bunker in the above photo were filled at a more gradual slope, as shown by the yellow line, silage could have been packed tightly and safely. The drawing below offers a way to fill a bunker safely, also allowing water to drain away from the wall.
Storing silage in bunkers or piles – while maintaining high quality with little waste at feedout – is an art involving some mathematics, says Brian Holmes, University of Wisconsin biological systems engineer.
“All too often, we see silage surfaces which are too steep. If they’re too steep, you’re not going to drive on them, and they’re not going to be properly packed,” Holmes told members of Wisconsin Custom Operators during their recent annual meeting.
“If you do drive on a steep surface, you run a high risk of tipping the tractor over. Sloping the filling surface down toward the (bunker) wall makes it tough to keep the packing tires tight against the wall to help preserve silage.”
Loosely packed silage results in more visible spoilage as well as increased safety risks and labor costs in pitching and disposing of the waste feed – something producers don’t like to do.
“If spoiled silage didn’t need to be pitched, feeders wouldn’t be up next to those feedout faces running the risk of riding an avalanche down to the floor,” Holmes pointed out.
He suggested a few ways custom harvesters can help clients avoid problems:
• Instead of maintaining a flat bunker-silo forage surface, fill a silo so forage slopes toward the bunker center (see drawing).
“Then, as you put in your capping layers, fill the middle and pack on a reasonable slope. That keeps you away from the wall while you’re packing that last section, leaving a channel for water to flow away from the wall. The other advantage: Your tractor leans away from the wall, allowing your tires to pack closer to the wall.”
Besides providing better at-the-wall density, the sloping-inward strategy keeps tires from tearing plastic that may line bunker walls, he said.
• Or an operator can top off a flat-surface bunker silo with silage pushed toward the center and redistributed to form a very gradual slope down toward the bunker wall. In the photo, the steep sides are not likely to be packed well and may be unsafe to drive on. Imagine the silage above the yellow line redistributed in the center of the bunker. The gradually sloped triangle holds the same amount of silage but allows it to be packed well and more safely, he said.
• Producers frequently construct silage piles too tall and steep to minimize the footprints of their storage-pad areas. “Many times they want to get as much silage on the site as possible, so they build taller. When they build taller for a given width, they end up with steeper sides.”
Such slopes are difficult to pack properly and effectively cover and hold the plastic close to the silage, Holmes pointed out.
He recommended a 3:1 gradual slope – 3’ horizontally for every foot of rise. Many piles are built so high that facers can’t reach the tops, again increasing the risk of avalanches (see “Surviving A Silage Avalanche”).
• If packing a bunker or pile over a number of days, consider covering the back portion, when it’s densely packed with a safe shape, to keep quality high and spoilage losses low.
• To get the most out of your packing time, and to accomplish it safely when using two or more tractors, make sure operators have a protocol, agreeing who has the right of way and how they will communicate with each other.