• Print
• Share

Biodegradable Plastic Mulches

Millions of acres of farmland are cultivated under plastic mulch worldwide. In Ontario, strawberry growers have adopted the use of plastic mulches for day neutral and some June-bearing strawberry production. These mulches are laid over the soil to warm the soil, suppress nutrient leaching and weed growth, and to conserve soil moisture. Despite being effective and affordable during crop production, the disposal of the mulch is increasingly costly and environmentally sensitive. It is estimated that for each acre of plastic, pick up and disposal costs are between $25 and $100 for labour and landfill fees (Rangarajan, 2006).

What Are Biodegradable Mulches?

Biodegradable plastic mulches are made primarily from plant starches and can be tilled at the end of the season, reducing labour costs for plastic removal and disposal. They can be broken down by micro-organisms in the soil such as bacteria, fungi and algae.

How Well Do They Work?

Prior to the onset of degradation, biodegradable plastics have a comparable level of performance to standard plastics. However, grower feedback has indicated that some degradable films breakdown unevenly, leading to large pieces of film blowing off the field and creating litter. Breakdown is primarily affected by temperature, sunlight, moisture, soil type, crop cover and weed pressure. This means that conditions which favour good crop growth also aid in mulch breakdown. Warmth, rain and UV exposure lead to increased micro-organism activity in the soil, speeding up plastic biodegradation. Soils with high levels of organic matter also tend to have high levels of microbial activity, increasing the speed of breakdown. As the mulch begins to degrade, weeds that grow through the gaps in the mulch with stretch it out and further speed breakdown (Rangarajan, 2006).

How to Succeed with Biodegradable Mulch?

The mulch must be stored in cool, dry temperatures, since it will begin to degrade in warm or moist environments. It should be stored upright on its ends, to avoid tearing holes in the roll which will be sites of early degradation once laid.

During application tension should be kept off the roll, and laying should be done in the cooler temperatures of the early morning to reduce stretch, which promotes faster mulch breakdown. Mulch should be laid immediately before planting, since exposure to sunlight and moisture will initiate breakdown (Rangarajan, 2006).

What Have Researchers Found?

Much research is in progress to find the most suitable alternative to black plastic mulches in fruit and vegetable production. Using melons as a test crop, a product called Mater-Bi was similar in field application to black plastic, having good stretch and similar soil temperatures early in the season, and although breakdown in late July was apparent, no difference in yield or average fruit size could be found (Rangarajan, 2006). A product called Garden Bio-Film has also been tested with basil as a test crop. Despite some slight early degradation the Bio-Film was found to lead to taller plants and a higher plant weight (Miles et al., 2007). A study using strawberries as the test plant included three brands of biodegradable mulch; BioTELO, Ecofilm and BioBag AgroFilm Commercial. The researchers found that while BioBag did not lay as well as the other brands, and began to degrade quite early, the other biodegradable mulches performed as well as standard polyethylene mulch (Smith et al., 2008).

Growers who have used both plastic and biodegradable mulches for at least two growing seasons were satisfied with how it laid, lasted and dissolved in the field after either rototilling or disking at the end of the season, although part of the mulch can become tangled in an interseeder or rototiller. Some growers noted that the mulch is not typically strong enough to grow crops with close spacing, such as onions or garlic, and cannot hold up if frequently stepped on, as in staked tomato production.

While biodegradable plastic mulches appear to offer promising results, more research will need to be done in order to produce mulch which can break down more fully in the field and can withstand the stress of being laid by machines. Also, the price of biodegradable mulch compared to conventional plastics is still a barrier to widespread use (Ngouajio, 2008). However, this rapidly advancing technology shows promise for berry growers.

References:

Miles, C., Klingler, E., Nelson, L., Smith, T., and Cross, C. 2007. Alternatives to plastic mulch in vegetable production systems. Washington State University; Vancouver Research and Extension Unit, Research Report 2007.

Ngouajio M., R. Auras, R.T. Fernandez, M. Rubino, J.W. Counts Jr., and T. Kijchavengkul. 2008. Field performance of aliphatic-aromatic copolyester biodegradable mulch films in a fresh market tomato production system. HortTechnology 18: 605-610.

Rangarajan, A. and Ingall, B. 2006. Biodegradable mulch product testing. Cornell University Department of Horticulture. Research Report 2006.

Smith, B.R., Deyton, D.E., Sams, C.E. 2008. Biodegradable films as an alternative to plastic mulch in strawberry production. SRFC Research Funding. Progress Report for SRFC Project #2007-08.