With the necessity to carefully handle the cover and weight it down, some farmers end up questioning the need to cover at all. Yet, uncovered silage spoils by an average of 20% to 50% per pile, wasting a lot of good forage material and the effort spent on harvesting it. If you’re going to go through the trouble of cutting and chopping all that grass or corn, you should at least make the most of it. Building a few basic concrete bunkers can streamline the silage process each year rather than trying to build pads and silos out on bare soil. Design your bunkers to make silage production as easy as possible with a few considerations, including how you’ll cover them.
Automatic Roller Systems
Automated rollers clamp on to the silage cover material to draw it back and forth over the pile as needed. When designing large silage piles, that will take months to fully feed out, this kind of system significantly reduces labor. It’s also safer, since workers won’t need to walk on the pile or operate heavy machinery where it might knock the surface loose. If there is a collapse while the automatic roller system is working, it’s unlikely to damage the equipment or cover due to how it’s suspended.
Underlay Sheets for Full Control
Concrete bunkers, for silage production, are often recommended to farmers for runoff control to meet local pollution standards. However, concrete alone is far from an impermeable barrier between the silage leachate and the soil. It begins as a somewhat impermeable material, with only a minor capillary effect through the surface, but tiny cracks quickly form to let larger amounts of liquid through. Installing an underlay sheet of RPE is essential for both permanent concrete bunkers and temporary in-field silos. A flexible geomembrane is better suited to controlling runoff, especially if it’s made of the same material as the cover, for a tight seal between the two layers.
Cover Materials to Block UV Exposure
In addition to weighing down the material in a bunker, you should consider ways to reduce the UV exposure on the cover. Even covers rated for decades of exposed use will benefit from some amount of UV blocking. A common solution is to suspend shade cloth over the top of the bunker to leave space between the height of the pile and the net. A UV-reduction shade cloth controls heating in the pile while also extending the life of the cover material. Other options include choosing weight materials like soil that hold down the cover while blocking light exposure or installing a thin surface layer of a UV resistant film or spray.
Bunker Height and Stability
Aside from its overall size and depth, the bunker’s walls are the primary feature that changes from farm to farm. Some farms keep bunker walls low and build piles that tower above them, while others aim to keep piles far below the height of the wall. So which design and use method is correct?
In general, it’s far safer to keep silage piles lower than the height of the bunker walls. If it is necessary to go higher, gently curve the pile so the only higher areas are concentrated in the middle. The USDA displays some of the worst and most dangerous silage piles they inspect every year, and many feature towering cliffs of silage packed tight against and above bunker walls. This is a constant collapse risk and puts inappropriate amounts of pressure against the concrete panels. To maintain the stability of a pile and its bunker, always design the space so silage is packed only 75% of the way up the walls or less.
Access to Bunker Walls and Pile Top
Thin panel walls are inexpensive to build and can take the weight of wet silage pressing against them with proper reinforcement. However, they do little to help workers access the top of the pile as needed. Building thicker walls and finishing out the tops to serve as walkways can make it easier to test and maintain the pile without walking on the cover material as much. There are also plenty of metal walkway attachment options to build scaffolding or frames across the width of the bunker, allowing you to walk to any point over the top of the silage pile and sample it. Install sighting rails, which also function to help loaders see how high they’re packing material, to double as safety rails for workers walking along the walls.
Cleaning and Storage Between Seasons
Most farmers plan to clean and store their silage covers between seasons to reduce unnecessary wear and tear on them. Yet, few consider the sheer size of a folded piece of RPE when it’s sized to cover a massive silage pile. Since these covers are kept whole, whenever possible, to reduce oxygen and water infiltration, they’re quite a chore to fold and carry by hand. Many farmers find they need to invest in tractor attachments, or least adapt the ones they have, to tackle this seasonal chore. You may just need to bring in some temporary laborers for the day since having more hands makes the job much easier to accomplish manually.
Drainage Concerns
As you site and layout the angles of the concrete bunker, keep drainage in mind. Even the most impervious combination of concrete and geomembrane at the base can’t keep a silage pile dry if flooding occurs and water is funneled directly into the pile by the ground. Grading, sloping, and installing trenches and ditches to direct water away, are all worth the effort during the installation of a bunker. It’s far more work to bring in the heavy equipment to redo these kinds of features later. In fact, you may have to dig up poured concrete slabs if the problem is severe. If you’re not sure how to design a bunker on your particular site due to drainage issues, request help from the nearest agricultural extension to get an on-site inspection and practical advice. Installing roofs over bunkers is a costly solution, but it’s often the only option in areas where high water tables or poor drainage make silage otherwise unfeasible.
Wedge or Flat Layers
When packing silage into a pile in a walled bunker, it’s possible to establish the various layers of material in two different ways. Many farmers mistakenly assume that applying perfectly flat layers of material over the top will provide the most strength to the pile. Yet, consider that you won’t be removing the feed again from the top in these layers, but rather from the front. These layers will quickly destabilize due to the weight of the top material pushing down the front face. Instead, try for the wedge formation when packing a bunker. Aim for a 3 to 1 slope where there’s only a foot of vertical rise for every three feet of horizontal run. If you want to pack the pile to 10 feet eventually, make sure it’s at least 30 feet wide to maintain the right angle of repose so there’s less chance of collapses later as feed is removed.
Silage bunkers are worth the extra effort and cost because they give you a controlled environment for producing feed. If you’re designing new bunkers or trying to renovate old ones, we can answer your questions about using RPE for liners or covers here at BTL Liners.
