When driving through agricultural areas, one often sees large, round bales of forage wrapped tightly in plastic film of various colors. This wrapped forage is not traditional hay, but is instead silage or haylage, a fermented feed product. The plastic wrap is a functional component of the feed preservation process, and its color is a specific tool used by farmers to manage the bale’s internal temperature.
The Necessity of Airtight Wrapping
The purpose of wrapping forage is to create an anaerobic, or oxygen-free, environment within the bale. Forage grasses are harvested at a higher moisture content than dry hay, which allows for the ensiling process to occur. Once the bale is wrapped, the trapped oxygen is quickly consumed by the plant cells and aerobic microorganisms.
This depletion of oxygen signals the start of the preservation process, which relies on beneficial microorganisms, primarily lactic acid bacteria. These bacteria ferment plant sugars into organic acids, such as lactic acid. This acid rapidly lowers the forage’s pH level, effectively pickling the grasses and preventing the growth of spoilage organisms like molds and yeasts. The tight seal of the plastic maintains this preserved state until the feed is needed.
How Color Dictates Heat Management
The fermentation process naturally generates heat, which must be managed to ensure bacteria thrive and forage quality is maintained. The ideal temperature for the silage mass is between 70°F and 100°F. Temperatures above 115°F to 120°F are detrimental, causing heat damage to plant proteins and lowering the feed’s nutritional value.
The color of the plastic wrap directly influences the bale’s temperature through solar radiation absorption and reflection. Dark colors absorb a greater percentage of the sun’s energy, while light colors reflect it. The film is composed of low-density polyethylene (LDPE) and manufactured with ultraviolet (UV) stabilizers. These stabilizers prevent the sun’s rays from degrading the material and compromising the airtight seal.
Practical Applications of Specific Wrap Colors
Farmers choose the wrap color based on their local climate and the time of year they are baling. White plastic wrap is the color of choice in regions with high ambient temperatures or intense sunlight. Its bright surface reflects the maximum amount of solar radiation, minimizing heat absorption and preventing the bale from overheating past the temperature threshold that damages protein. This reflection keeps the fermentation process within the desired temperature range.
Conversely, black plastic wrap is used to maximize heat absorption, which is beneficial in colder climates or during cooler seasons like early spring or late fall. The solar gain from the black wrap helps elevate the bale’s temperature, ensuring fermentation is successful. This heat absorption compensates for low ambient temperatures that might otherwise slow down the activity of the lactic acid bacteria.
Green plastic wrap serves as a moderate option, offering a balance between the reflection of white and the absorption of black. It is utilized in temperate zones where temperature fluctuations are not extreme, providing a suitable compromise for heat management. Additionally, farmers may use different colors to code the bales, distinguishing between forage types or cutting dates for inventory management.
The Composition and Disposal of Bale Wrap
The film used to wrap silage bales is a specialized plastic, often low-density polyethylene (LDPE) or linear low-density polyethylene (LLDPE). This material is selected for its strength, stretch-ability, and ability to create a durable, hermetic seal when stretched tightly around the bale.
Once the feed is consumed, the disposal of this specialized plastic presents a significant logistical and environmental challenge for the agricultural industry. Since the film is often heavily contaminated with dirt, moisture, and residual forage, it is difficult and costly to recycle through standard municipal streams. For this reason, many areas have developed specialized agricultural plastic recycling programs that require farmers to clean and compact the used film before it can be processed into pellets for reuse in other plastic products.