Plastic mulch films are used extensively by growers in the vegetable, nursery and landscape industries for retaining moisture, controlling weeds, warming the soil in early spring, improving crop yield and quality, protecting plants in winter and accelerating plant growth for earlier harvests. Over the years, the consistent challenge has been the high cost of disposing of the plastic once it's been used.
Researchers at Michigan State University hope an ongoing interdisciplinary research study will help create more profitable and sustainable production practices for these industries.
The stage for the current project was set in 2005 when Mathieu Ngouajio, MSU assistant professor of horticulture, presented a seminar at MSU highlighting results of research he had been conducting since 2002 evaluating various types of plastic mulches used by the vegetable industry. After he described the limitations he was facing with disposing of used plastic, Tom Fernandez, an MSU colleague in the Department of Horticulture, approached Ngouajio and explained that the nursery and landscape industry faced a similar dilemma -- how to dispose of plastic used to cover growing crops and the tops of greenhouse buildings to retain heat. Ngouajio and Fernandez decided to work together to seek a solution for both industries.
To address industry needs, Fernandez and Ngouajio teamed up with plastics chemists Rafael Auras and Maria Rubino from the MSU School of Packaging.
The first step taken by the MSU researchers was to design a biodegradable mulch film for the fresh market vegetable industry. Once a viable product is developed, researchers will shift their attention to modifying the product to meet the needs of the state's landscape and nursery industry. The common denominator for the state's vegetable, nursery and landscape industries is the high cost of plastic disposal.
"Getting rid of the used plastic is very expensive, and it's an annual expense for vegetable growers," Ngouajio says. "Growers pay for labor to cover the fields with plastic and then to have it manually removed at the end of the season, loaded onto a truck and driven to the landfill, and then they have to pay the landfill to take the plastic. These costs are all in addition to the cost of growing the crop. Growers would really benefit from the creation of a biodegradable alternat ive."
Plastic mulch films are used on a variety of vegetable crops in Michigan, including 11,600 acres of fresh market cucumbers, peppers and tomatoes. On this acreage alone, about 165 pounds of plastic is used per acre, for a total of 1.9 million pounds. The cost to dispose of the plastic films amounts to $49 per acre, for a total of $568,400.
"Disposal doesn't only represent a huge expense to growers – it also adds nearly 2 million pounds of waste plastic to landfills, which is a real environmental concern," Ngouajio says. "Our research is focused on developing a biodegradable mulch film that will help reduce grower expense and eliminate excess waste in our landfills."
Researchers have focused their efforts on designing plastic that could be broken down by soil microbes and successfully developed three biodegradable mulch films, which were field tested with tomatoes last summer at the MSU Horticulture Teaching and Research Center. Researchers are evaluating data collected during the 2006 growing season, comparing the effect of the biodegradable material on crop performance and yield to that of conventional black plastic film.
"This is truly an interdisciplinary project," Ngouajio says. "Chemists in the MSU School of Packaging are evaluating the physical and chemical properties of the film to determine how they break down and change color over time. Researchers in the Horticulture Department are evaluating tomato yield, weed control and soil temperature, and so far, results appear promising."
Once the data have been analyzed, plastics chemists will modify the film properties on the basis of the lab results for the 2007 crop year. They also plan to make the plastic for future studies by using the extruding equipment housed in the MSU Packaging Laboratory.
"The materials used last summer were manufactured in India because they have the processes and equipment in place to make large volumes of it," Ngouajio explains. "We did an extensive study last year and used a large amount of plastic, but now that we know how much we need and the needed mulch film properties, we hope that, in the near future, it will be possible to use the small machine we have here on campus to produce it."
Though Ngouajio admits that purchasing biodegradable mulch will be slightly more expensive for growers than buying conventional films, at the end of the use cycle it will be a more profitable alternative.
"A biodegradable product will likely cost more to purchase, but it will be more environmentally friendly to use. Biodegradable materials wear down in much the same way that cornstarch breaks down, so it will be able to be broken down by the soil and won't need to be dumped in landfills," he says.
"MSU is working hard to address the needs of the state's vegetable growers by finding sustainable ways to make the use of plastic mulch more profitable for producers and less damaging to the environment," Ngouajio says.