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New Mexico State University

New Mexico State University

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Compost, Gels Help Conserve Moisture in New Mexico Gardens

LAS CRUCES -- El Niņo year or not, New Mexicans should look for ways to conserve water in their gardens, such as using compost and water-holding gels.

"It's important to make every drop of water count when growing crops in New Mexico," said George Dickerson, horticulture specialist with New Mexico State University's Cooperative Extension Service.

Dickerson noted that drought frequently follows wet years in the Southwest. He said summer storms don't always provide much soil moisture for crops.

"We may have heavy thunderstorm activity during the summer here in the desert, but it often runs off and is unusable," he said. "If you can hold the moisture on site, it could mean the difference between a crop and no crop."

Adding compost is a traditional way to increase soil's water-holding capacity, especially with sandy soils. Compost also will help improve the aeration of heavier clay soils, allowing water to penetrate the soil, Dickerson said. Besides helping soil hold water, compost is an excellent low-analysis fertilizer, meaning it slowly releases small amounts of plant nutrients.

"We've also been looking at using water-holding polymers or gels that will absorb 400 times their weight in water," Dickerson said. "The majority of this absorbed water is then available for plants." The garden gels are similar to materials used in disposable diapers.

Last summer, Dickerson tested water-saving techniques at eight on-farm demonstration plots throughout New Mexico. The Extension project evaluated the effects of gel and green waste compost from the City of Albuquerque on vegetable production, using limited irrigation.

Various amounts of gel were used alone or with compost. To hold in more moisture, vegetable plots were covered with woven, black plastic mulch. Cantaloupes, tomatoes, chile and other transplants were inserted through the plastic, watered once or twice for establishment, and then allowed to grow under natural rainfall.

"Water savings varied from 62 to 93 percent in these plots," Dickerson said. "Although crop production was better where we received more rainfall, the water savings was highly significant." Rainfall varied from approximately 2 1/2 inches at Arroyo Seco near Taos to more than 12 inches at Edgewood.

"This year, we plan to continue some of our demonstration plots and set up two replicated research plots," Dickerson said. "The system looks very promising, but replicated research plots will help us confirm whether our results will be consistent."

Because applying gels to gardens and covering them with plastic is expensive, only high value crops should be grown in such projects, Dickerson said. In the demonstration projects, after deducting the costs of supplies (plastic, gel, fabric pins, transplant tubes and compost), modified net returns varied from $235 to $2,895 per thousand square feet.

"Modified net returns have to be considered with some caution because we didn't include labor in the estimates," Dickerson said. "The beauty of the project, however, is that the plastic mulch has an ultraviolet light inhibitor in it, so it's guaranteed not to break down for a minimum of five years. The gel also resists breakdown, so you can replant the same plot over and over. Only the fertilizer has to be replaced."

Another advantage of using the mulch is that gardeners don't have to weed, except around the edges of the plastic, Dickerson said. They can also walk on the plastic between the plants even when the soil is wet, which means they can pick at any time. The black plastic also heats the soil, allowing earlier planting in the spring.