Silage tarps are used to ensure that your ensilage is protected from exposure to air, light, and excess moisture, both during fermentation, and the storage and feed-out stages. This protection is critical to producing high quality silage, so the selection of covering material needs to be carefully considered. You might start off by noting the thickness and density of the materials you’re considering, their durability and resistance to punctures or tears, and what layers they’re composed of. But that’s just the beginning of a thorough evaluation. Consider each of the specific goals individually and how you’ll approach them.
Air
High quality silage needs to be protected from exposure to air (oxygen) from the point it’s packed until it’s consumed by livestock. Anaerobic fermentation is the preservation mechanism of silage and it requires an oxygen-free environment. When forage is exposed to air, anaerobic activity is interrupted and a wide variety of microorganisms that cause food spoilage are able to grow. Even when silage is being fed out, the effects of low quality fermentation appear as aerobic instability. Silage that’s aerobically unstable degrades and begins to spoil rapidly as soon as it’s exposed to air.
Horizontal silos, such as bunker, pile, and trench styles, need to be tightly covered by a flexible material that conforms closely to the surface of the forage mass. Spaces between the cover and the silage material indicate air pockets and possible points of contamination. A series of weights, such as sandbags or used tires, are usually spread across the cover to prevent wind lifting, to maintain close contact with the silage material, and, to a certain extent, help maintain compaction in the top few inches of the pile.
Silage covers need to be airtight and also need to be durable enough to withstand foot traffic and the placement of heavy weights over the surface. If hay bales are used as weights, the cover material also needs to be able to withstand pokes and scratches from dry hay stalks.
Light
Silage needs to be processed and stored in complete darkness for best results. Algae, in particular, thrives in the rich nutrient environment of silage, and it needs little more than light to begin to photosynthesize and reproduce. Like all green plants, algae emits oxygen when exposed to light (during the daytime, for example), and oxygen is the enemy of anaerobic fermentation. Algae exists in many forms, including microscopic varieties, so you probably won’t be aware of a problem with algae until your final product is spoiled or rapidly breaks down in the presence of oxygen (aerobic instability).
Silage covers should be thick or densely woven enough to eliminate light transference, but the material also needs to be resistant to tiny punctures from sharp stems or prickly leaves.
Moisture
The moisture level in silage must be carefully controlled throughout the ensiling process. Excess moisture supports the growth of Clostridium bacteria which consume carbohydrates, protein, and lactic acid as they produce butyric acid. When butyric fermentation dominates, the silage will have a higher pH compared to lactic acid fermentation, and the resulting silage will not only be low in energy and nutrients, but aerobically unstable and vulnerable to rapid spoilage. As excess moisture moves through and the silage, it carries large volumes of digestible nutrients which escape in the form of seepage.
Silage seepage is one of the most polluting organic materials that a farm produces. It’s highly acidic and extremely corrosive. Untreated seepage that escapes into the environment can poison the soil, compromise groundwater supplies, and cause severe damage to aquatic ecosystems, including fish kills and toxic algae blooms.
Of course, moisture levels at harvest and ensiling aren’t the only concern. Rainwater that enters bunkers, pits, and piles can also trigger seepage problems even in properly ensiled materials. Horizontal silos should be constructed to prevent precipitation from entering with a system of berms and covers, and include a drainage system to capture and divert any seepage or leachate that does escape.
Silo covers need to be impermeable to water so that even heavy rain won’t soak through, and they also need to be placed and anchored in a fashion that will prevent movement of water between the ensiled material and the wall of the enclosure (bunkers and pits).
Choosing a Material
We’ve discussed three critical roles your silo cover should fill, but no single product or system is perfect, so you’ll need to strike a careful balance between the strengths, weaknesses, cost, and utility of each of them to find the right solution for your operation.
- Weight
Heavy covers can be difficult to deploy, so the thickest and heaviest material isn’t necessarily the best option. Look for a lightweight material that offers exceptional durability and damage resistance.
- Durability
Sheet material that tears when it catches on a snag, or gets punctured when someone walks across the surface of a silage bunker won’t provide the kind of protection you need. Look for a reinforced material that’s designed to resist both punctures and tears. If it’s elastic, make sure it’s able to return to its original shape without deformation, and if you’re in a climate with extreme winters, make sure the material you choose doesn’t become brittle or prone to cracking in low temperatures.
- UV Resistance
Many plastics are extremely vulnerable to degradation from UV rays in sunlight. Since your silo cover is itself intended to protect the silage from UV rays, you’ll obviously need a cover that can tolerate full sun exposure for many months at a time. For example, carbon black is added to many plastics in order to slow or prevent absorption of UV radiation that can impact flexibility, mechanical strength and opacity.
- Flexibility
A silo cover needs to be able to conform to the shape of the structure, including corners, bends, and irregular surfaces, especially if it’s being used as part of a rain capture & diversion system. Many plastics are stiff and difficult to bend or fold, and a few of them can even crack or permanently crease. Look for a liner that is easy to manipulate and that maintains flexibility even in cold weather.
- Colors
It may be tempting to decorate your silos with the colors of your alma mater’s championship football team, but in this case, basic black and white is really your best choice. Look for a cover that’s black on one side, and white on the other. The black side should be placed down, facing the silage material. Its job is to prevent light transference and provide UV stability. Carbon black is an excellent material for this surface. The white side should face up, towards the sky. Its job is to reflect thermal energy (heat) from the sun, preventing the silage pile from overheating.
