What does biodegradable mulch cost?The purchase price of biodegradable plastic mulch varies, generally based on its size (roll width and length) and thickness. Thickness of mulch products can range from 0.5 to 1 mil, with thinner products generally degrading faster than thicker products. The cost of biodegradable plastic mulch products ranges between 3% and 60% higher than traditional plastic mulch, depending on the product thickness and size (click here for more information). Both clear and white-on-black biodegradable mulch is more expensive than black biodegradable mulch. Prices of cellulose-based (paper) mulch also varies based on thickness and creping, but is priced similarly to biodegradable plastic mulch.
Although the purchase price is higher for biodegradable mulch, there can be labor and equipment use savings associated with using a biodegradable product since it is tilled into the soil instead of removed from the field at the end of the season. Our USDA SCRI research and extension project is currently conducting farm budget studies and life-cycle assessments of biodegradable mulches to better understand these costs and potential savings.
How do you apply biodegradable mulch in the field?Application of biodegradable mulch uses the same equipment as traditional plastic mulch. Either a raised bed mulch layer or a flat-bed layer can be used. Both tractor-pulled mechanical layers and hand-pulled layers are available. Several manufacturers of biodegradable mulches recommend releasing tension on the mechanical layer so that the product is not stretched or torn during laying.
What does it break down to?After the mulch is tilled into the soil, microorganisms in the soil break down the biodegradable plastic mulch mainly to water, carbon dioxide, and biomass. The goal of our USDA SCRI research and extension project is to conduct field trials and extensive soil testing to confirm that the products do completely degrade.
Will biodegradable plastic mulch work?Biodegradable plastic mulch products are designed to provide the same weed suppression, moisture retention, and soil temperature altering benefits that traditional plastic mulches do. Thicker products are commonly used for crops that have a long growing season, or for double cropping where slower degradation is desired. Climate is also considered when selecting a product. Preliminary research conducted through our USDA SCRI project shows that the products are performing as designed, productivity is similar to that achieved with conventional polyethylene mulches, and weed control exceeds bare-ground growing methods.
The products biodegrade after they are tilled into the soil. Rate and extent of mulch biodegradation varies based on the product and the soil microenvironment. Paper mulch biodegrades rapidly, and within six months of soil-incorporation, little is visible to the human eye. Biodegradable plastic mulch is fragmented by tillage, and fragments are reduced in size over time, but it is still uncertain how quickly or completely they biodegrade under field conditions. The components of biodegradable plastic mulch have been shown in laboratory studies to be biodegradable. Our USDA project will assess biodegradable plastic mulch decomposition in the soil under field and laboratory conditions.
What are biodegradable plastic mulches made of? Are all components biobased?The specific composition of biodegradable mulch products is proprietary information retained by the manufacturers. The composition of biodegradable plastic mulch is not all biobased (derived from plant sources). Commercially available products vary in their bio-based content and range from less than 10% bio-based up to 20% biobased. Generally, the products are composed of some combination of polyesters (a group of polymers, distinguished because they contain an ester bond that is readily broken by microorganisms, sunlight, and water; they may be derived from synthetic or natural sources) and starches. Polyesters commonly used to make biodegradable plastic mulch include:
- Polybutyrate adipate terephthalate (PBAT): a synthetic random copolyester of adipic acid, terephthalic acid, and 1,4-butanediol. The ester bonds contribute to PBAT’s biodegradation.
- Polylactic acid (PLA): a thermoplastic polyester, derived from starch (e.g., corn, sugar beet, tapioca, or sugar cane) fermented by microorganisms to produce lactic acid, which is then polymerized synthetically through a series of reaction steps. PLA can be produced relatively inexpensively in large quantities compared to other biobased biopolymers.
- Polyhydroxyalkanoate (PHA): a polyester created by a natural, one-step bacterial fermentation of plant sugars and/or lipids.
Where is it marketed? How do I get it?Biodegradable mulches are available from several farm supply distributors, and some products can be obtained directly from the manufacturer. Manufacturers often consult with producers to assure the producer is ordering a product that is the proper thickness for his or her climate and cropping system. A list of manufacturers is available here. Other manufacturers and products may be found in farm supply catalogs or an online search.
Will it store for over a year?Biodegradable mulches are designed to biodegrade, and weathering and microorganisms will eventually break the products down. Manufacturers do not recommend storing the product for more than one year (i.e., a purchased product could be used for two seasons). Storage should be in the product’s original wrappings or containers, and indoors if at all possible to reduce exposure to temperature fluctuations, direct sunlight, high humidity and precipitation.
Are there reflective (with a metallic side) or white versions of biodegradable plastic mulch available?Manufacturers of biodegradable plastic mulches produce clear, white, and white-on-black versions. To our knowledge there is currently not a metallic-sided product. Black mulch provides soil warming that may not be desirable for all cropping systems and locations. Black mulch warms the soil because black absorbs the solar radiation, and the product transmit that energy to the soil if it sufficiently contacts the soil. The alternative white and white-on-black products are offered by some manufacturers for use where soil warming is not a desired benefit. Because white will reflect solar radiation, both white and white-on-black mulches will decrease the soil temperature. Clear plastic mulch may produce greater soil warming than black mulches because they transmit solar radiation to the soil and if water condenses on the under side of the mulch it prevents outgoing infrared radiation.