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New Mexico State University

New Mexico State University

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Plastic Mulch Conserves Water, Controls Weeds In High-Value Vegetable Crops

LAS CRUCES -- An Edgewood farmer produced more than 40 tons of pumpkins per acre with fewer than 11 inches of moisture during 1998 -- a drought year in New Mexico. His secret: conserving water with black, woven, polypropylene mulch.

The farmer was part of a three-year drought project, conducted by New Mexico State University's Cooperative Extension Service, which began in 1996. "Our goal was to determine whether high-value crops like transplanted vegetables could be grown under semidry conditions," said George Dickerson, NMSU Extension horticulture specialist. "We wanted to produce a crop with limited irrigation, while eliminating weed problems."

At various locations across the state, Dickerson applied black, woven, polypropylene fabric mulches to vegetable plots. "The mulches allowed water to pass through to the soil while reducing weed growth and moisture evaporation," he said.

On most sites, he also incorporated water-absorbing polymer crystals into the soil. These crystals look like rock salt when dry, but have the ability to absorb as much as 400 times their weight in water. "When mixed with the soil, the crystals act as a water reservoir, returning the majority of absorbed water to the growing plants," Dickerson said. Supplemental irrigation water was applied only when necessary.

"During the first year, plots with the water-holding polymer showed improved growth and yield," he said. "However, in the second year, results were mixed. It's possible that salts in the soil and irrigation water may have reduced the polymer's effectiveness."

The greatest improvements in yields and water savings were on plots with the black mulch. "Most of the sites produced excellent crops, using 50 percent less water," Dickerson said.

The fabric mulch also reduced time spent weeding compared to untreated plots. Bindweed infested the untreated plots, requiring 80 percent more weeding time than in mulch-covered plots.

"Another benefit of the black mulch was its ability to warm the soil, resulting in earlier production," he said. "Ultraviolet light inhibitors in the mulch extend the material's useful life. After three years in production, the mulches at all locations were still in relatively good shape."

Many of New Mexico's major agricultural crops require at least 3 acre-feet of water for maximum production. "We've proven that the amount of irrigation water can be reduced with black, woven, polypropylene mulches," Dickerson said.

The mulches also are useful for home gardeners. "Most people don't like to weed. The benefit of saving on your water bill is just icing on the cake," he said.