Disappearing Mulches

09/01/2010 02:00:00 AM

Ideally, after harvest, growers till a biodegradable mulch into their fields, where soil microorganisms convert it into water and carbon dioxide.

Researchers will bury samples in the soil and check them over time to determine how long that process takes.

Tweaking the formula

The first growing season showed the new material holding up “pretty well,” degrading at a rate somewhat less than anticipated, Hayes says.

Inglis says too much light penetration seems to be allowing more weed germination beneath the film.

Tweaking the formula for next year’s trials should address both issues.

“The rate of biodegradation has to be a happy medium between not too fast and not too slow,” says Randy Shogren, research chemist at the U.S. Agriculture Department’s National Center for Agricultural Utilization Research in Peoria, Ill.

Shogren developed a paper mulch coated with vegetable oil-based resins that performed well in the field; it also resists some weed species that poke through plastic. But to avoid tearing the paper during application, mulch-laying machines must run at slower speeds.

Thornton has tried paper mulch in the past. “It holds up on the surface, but where you have to bury it, it rots in six weeks,” he says.

Orzolek, at Penn State, is working with a bioplastic derived from plant sugars that should hit full commercial production next year. Mirel mulch, from Cambridge, Mass.-based Metabolix, degrades in two to three months after it’s plowed into the soil, he says.

Ngouajio’s research on a biodegradable plastic polymer is on hold pending additional funding. Two years of field tests showed promise, but he hopes to improve the material to speed conversion by soil microbes into water and carbon dioxide components.

Goal: No disposal

The goal for a biodegradable mulch is a complete breakdown in the soil before the next growing season begins. That step also is needed for acceptance by organic growers, Ngouajio says.

Most biodegradable mulches on the market now are based on starches, particularly from corn. The possibility of those products incorporating starch from genetically modified corn also makes organic growers leery, Ngouajio says.

Biodegradable mulches will cost more up front—Orzolek estimates $150 to $180 per acre, compared with $80 per acre for a product growers must remove from their fields—but should reduce overall mulching expenses.

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