May 19, 2003

WESLACO -- For years, Lower Rio Grande Valley farmers have been laying row after row of plastic sheets in their vegetable fields.

Plastic mulch atop planting beds helps grow healthier, more abundant crops in a shorter period of time. Plants grow right through holes punched in the plastic and drip lines under the plastic use much less water than flood irrigation.

Plastic mulch has been used successfully in South Texas for years on a variety of high-value vegetable crops. But new studies are showing that colors other than the standard black used here almost exclusively may perform better.

Dr. Bob Wiedenfeld, a soils scientist at the Texas A&M System Agricultural Research and Extension Center at Weslaco, has been working this year with Ampacet Corp., a company that produces many types of plastic mulch that differ in color, composition, texture, finish and transparency.

"The goal of plastic mulch," said Wiedenfeld, "is to raise the soil temperature, and we'd like the plastic to be durable, to stand up to our high winds. So we're comparing Amapcet's different plastic films to see which ones perform best here."

In January, Wiedenfeld installed a rainbow of different plastic mulches on a research field plot at the center. Drip lines down the middle of beds are currently providing water and fertilizer to a watermelon crop, while drip lines on either side of the bed will tend to fall peppers when they are planted. Each plastic mulch is evaluated by measuring vine lengths of the watermelon plants and soil temperature.

The colors include red, blue, clear, silver, black, white and olive. Some films are shiny, others matte, some opaque, some translucent and one clear.

"The clear mulch has done the best job of warming up the soil and it appears to be the most durable. Unfortunately, clear plastic provides little or no weed control. The clear plastic serves as sort of a mini-greenhouse for weeds that push up the mulch," Wiedenfeld said.

Among the better performers so far for Wiedenfeld is a silver colored plastic that he said has produced extraordinary results in vine lengths of watermelon, as well as higher soil temperatures. Weed control also was good. Another film with a white surface and black undersurface is also performing well.

"The white on black film would do well for those fall crops that are planted in the heat of summer. The white on the surface reflects heat and cools the soil to protect the young plants, while the black underside keeps weeds from growing," said Wiedenfeld.

Mark Jordan, manager of Pliant Corporation, which actually manufactures the film using Ampacet additives, said plants react differently to different colors.

"Phytochromes (plant pigmentation that absorbs light waves) make the difference," he said. "The silver, for example, is used extensively in California and Mexico. It also showed great results in squash, tomatoes and peppers in studies at Penn State. The best film to use will probably depend on when and where you are going to use it and what results you want it to achieve."

Braionna Barber, an Ampacet development engineer, said her company is currently testing colored mulches in Mexico, Michigan, California, Indiana, Florida, Georgia and now Texas.

"We're testing in different regions to see what effects the different films have in each growing condition," she said. "In Michigan, where it's cooler, for example, the object is to trap heat and extend the growing season. Here, where it's much hotter, you want to reflect the heat onto the plant."

She said her company was also working on a photo-degradable film that is tilled into the soil after harvest, since removing the plastic at season's end is one of the biggest expenses of using plastic mulch.

Wiedenfeld said once the summer watermelons are harvested, a crop of fall peppers will be planted on the same mulches to determine durability of the films. Results, he said, should be available by year's end.

For more information, or to visit the colored mulch research field plot, contact Wiedendfeld at (956) 968-5585.