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Let's Improve Bunker Management


Let’s Improve Bunker Management

By Bill Seglar

Many farms still miss the mark when it comes to managing bunkers. Are you packing and covering your silage properly?

Oxygen is the enemy . . .

Spoilage microbes (primarily yeast and molds) require oxygen for their activity, therefore the benefit of efficient and effective packing is the exclusion of oxygen. At harvest, the quicker oxygen is excluded, the more efficient the front-end fermentation can be (providing increased dry matter recovery). At feedout, the more densely packed the forage and the less oxygen infiltration at the face, the less secondary fermentation (shrink) can occur.

The simplest way to demonstrate the impact of oxygen: Think of the depth of the slime layer of an uncovered bunker six months after storage (usually 6 to 12 inches). Compare that to a well-packed, plastic-covered bunker (2 to 4 inches).  Next, compare that to a bunker with a layer of oxygen-barrier plastic (near zero).

The value of going from average management (15 percent storage plus feedout shrink) to a great management (10 percent shrink) is at least $3,000 per 100 cows per year (assumes 1,000 tons corn silage annually per 100 cows). Much of that improvement centers around reduced exposure to oxygen. For those questioning the math, remember that the shrink is at the cost of highly digestible nutrients - the bugs consume readily available carbohydrates such as sugars, not fiber, and therefore corn meal equivalents can be used to calculate shrink value as shown in the table below.  The $3,000 value is determined by calculations that drive the following table where using $5.00/bu corn and reducing shrink from 15 to 10% results in an increased $3.15/ton silage savings, therefore the 1,000 ton silage example calculates out to $3,150.  Therefore, the cost of replacing that dry matter is essentially the cost of corn grain, not corn silage. If you are using most of the good management practices listed below but only have average density, you are leaving money on the table.

Cost chart

Haylage . . .

Given that hay silage is usually considered more difficult to pack, many hay silage bunkers meeting density targets. (Remember, though, a majority still could be improved.) It comes back to tons per hour delivered to the bunker where tons/hr of corn silage delivered to the silo for packing compared to hay crop forages. Even if you harvest twice as many acres per hour with hay silage, the tons per hour for first crop would likely be about 50 percent of the corn silage and even lower for subsequent cuttings. This gives the packing tractors a chance of keeping up.

Reach an optimum silage density

Many beef and dairy producers are not achieving the recommended minimum silage DM density of 15 pounds per cubic foot (Muck and Holmes, 2007, and Visser, 2005). Producers should pack and cover silage to exclude air, which reduces fermentation loss. Silage density and shrink loss are inversely related, so as packing density increases, shrink loss decreases. The goal should be to have a silage density of 15 to 18 pounds of DM and 43 to 51 pounds of fresh weight per cubic foot at 35% DM. If producers increase density by 2 or 3 pounds of DM per cubic foot, that translates to a reduction in shrink loss of about 3 to 5 percentage points.

To improve density, several key considerations from Brian Holmes, University of Wisconsin-Madison, and Keith Bolsen, Kansas State University Professor Emeritus, include:

  • Check silage densities. But only do this if it can be done safely, and be prepared to adjust filling and packing procedures.
  • Reduce forage delivery rate. This is difficult to accomplish, as few producers and silage contractors are inclined to slow the harvest rate.
  • Employ well-trained, experienced people. Particularly those who operate the push-up/blade tractor or tractors. Provide training as needed and emphasize safety.
  • Increase rate of forage push up and packing. By increasing this and the harvest rate, producers will reach the target density.
  • Spread forage consistently. Do this continually in thin layers of 6 to 8 inches during the entire filling and packing operation.
  • Increase packing tractor weight. Increase the number of packing tractor passes over all forage layers. Caution: Additional tractor passes require more packing time per ton.
  • Increase packing passes near the walls. Consider this to increase density in that area of the silo.

Management steps to minimize or prevent surface-spoiled silage

  • Shape all surfaces so water drains off the bunker or pile. The back, front and side slopes should not exceed a three-to-one slope. Seal forage surface immediately after filling is finished.
  • Two sheets of plastic or a sheet of oxygen barrier film are preferred to a single sheet of plastic.
  • Overlap sheets that cover forage surface by a minimum of 4 to 6 feet.
  • Arrange plastic sheets so runoff water does not come in contact with silage.
  • Sheets should reach 6 feet off the forage surface around the perimeter of a drive-over pile.
  • Put uniform weight on the sheets over the entire surface of a bunker or pile, and double the weight placed on the overlapping sheets. Bias-ply truck sidewall disks, with or without a lacework of holes, are the most common alternative to full-casing tires. Sandbags, filled with pea gravel, are an effective way to anchor the overlapping sheets, and sandbags provide a heavy, uniform weight at the interface of the sheets and bunker silo wall. Sidewall disks and sandbags can be stacked; if placed on pallets, they can be moved easily and lifted to the top of a bunker wall when the silo is being sealed and lifted to the top of the feedout face when the cover is removed. A 6- to 12-inch layer of sand/soil or sandbags is an effective way to anchor sheets around the perimeter of piles.
  • Prevent damage to the sheet or film during the entire storage period. Mow the area surrounding a bunker or pile and put up temporary fencing as safeguards against domesticated and wild animals.
  • Regular inspection and repair are recommended, because extensive spoilage can develop quickly if air and water penetrate the silage mass.
  • For many years, full-casing discarded tires were the standard tools used to anchor polyethylene sheets on bunkers and piles. However, these tires are cumbersome to handle and messy; in addition, standing water in full-casing tires can provide a breeding ground for mosquitoes that may carry the West Nile virus.

If you understand, apply, and excel at the above management package, don't let poor packing and covering be the weak link and money wasted in your forage program.


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