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Hoop House Designs Being Tested For Winter Vegetable Production

New Mexico State University is in its third season of testing hoop houses for winter vegetable production.

Late October and mid-November might seem late to be planting salad greens in New Mexico, but a group of New Mexico State University faculty members, students and farm crew were not deterred by custom.

For the third year in a row, they were starting rows of Trout’s Back lettuce and Bloomsdale spinach from seed in a dozen hoop houses, also known as passive-solar high tunnels. Six of the structures are located at NMSU’s Leyendecker Plant Science Research Center south of Las Cruces and the other six are at NMSU’s Sustainable Agriculture Science Center at Alcalde, north of Santa Fe.

When the last of this crop is harvested in late winter or early spring, it will provide the final data in a three-year study of the viability of these low-budget greenhouses for New Mexico small producers who want to grow vegetables in the winter.

This project, titled “Winter Production of Leafy Greens in the Southwestern U.S.A. Using High Tunnels,” actually involves 18 hoop houses—in addition to the ones at the two agricultural science centers, there is one at each of six cooperator sites in New Mexico, Arizona and Colorado. The project is funded by a $194,000 grant from USDA’s Western division of the Sustainable Agriculture Research and Education program.

The project’s lead researcher is Steve Guldan, agronomist in the Department of Plant and Environmental Sciences and the superintendent of the Alcalde science center.

“During an advisory committee meeting a few years ago, Don Bustos, a successful small-scale grower, recommended that more research was needed on year-round vegetable production,” said Guldan. “I felt that the USDA’s Western SARE program was an ideal source of potential funding for research on this topic.”

The project team includes three other faculty members and five Extension specialists from NMSU, plus a Colorado State University Extension agent from La Plata County. Two NMSU graduate students are intimately involved in the project, as well, and will be using data from the study in their master’s theses.

“The main goal of the project is to determine the best way for growers who want to engage in winter vegetable production to provide for direct markets such as restaurants, year-round farmers’ markets, community-supported agriculture projects, and maybe even schools,” said Guldan. “But we want to do it in a way that doesn’t require expensive heated structures—and to see if the types of passive solar structures in this study can provide the winter growing environment for some cold-hardy vegetables like lettuce and spinach.”

Juliette Enfield is a master’s student in PES who has participated in the project since its inception. “We’re growing lettuce and spinach because they’re two crops that are always in demand, and they’re good things to grow in a hoop house because they’re the most efficient use of space,” she said. “If you plant something like tomatoes, a lot of the space is being used for vegetation, not the actual product that you sell.”

“We have two replications of three different designs of hoop house at each of the two science centers,” said team member Mark Uchanski, a horticulturalist in the Department of Plant and Environmental Sciences and Enfield’s advisor. “The low design is a single layer of plastic covering up the frame of the hoop house. The medium end design is a single layer covered with a second layer, and a fan to blow air between the layers to provide insulation. And then the final, and high-end, design adds several 55-gallon drums, painted black, inside the hoop house that allow for the capture of heat energy during the day and then the re-release of that heat energy at night.��

Del Jimenez, NMSU Extension agriculture specialist with the Rural Agricultural Improvement and Public Affairs Project, has been developing low-cost hoop houses for several years and came up with the basic designs used in the study. The structures measure 16 by 32 feet and feature PVC pipe frames and translucent plastic sheeting. They are equipped with overhead sprinkler systems.

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Evaluation of the three designs involves analysis of the productivity of the two crops, measured in pounds of harvest, for each of the three years of the study. Productivity will be correlated with the type of house, the planting date and the location.

Fine tuning of the productivity analysis will involve temperature and moisture data. Each house contains equipment to monitor and log six data points of inside and outside air and soil temperature, sampled every 30 minutes between planting and final harvest.

It isn’t enough to show that a good crop can be grown under New Mexico’s winter conditions. The hoop-house approach must make economic sense, as well.

Evaluating the viability of hoop houses for actual producers involves weighing the costs of growing the vegetables, including the investment of building and maintaining an appropriately designed hoop house, against the anticipated income from the produce. That’s the focus of Connie Falk, a professor in the Department of Agricultural Economics and Agricultural Business, and her graduate student Emmanuel Hecher.

“The economic analysis involves a risk simulation model, which estimates the probability of the returns from selling each crop in each of the designs at each site, exceeding zero,” said Falk. “We examine the probability of returns being positive for a range of possible prices observed during the experiment in different markets. The first-year analysis indicates that the probability of positive returns in Alcalde for all prices is lower than in Las Cruces.”

When Falk and Hecher complete that analysis, farmers will be able to make an economically prudent decision about whether to build a hoop house and which model to select for their climate zone.

While definitive conclusions won’t be available until after data from the 2011-12 harvest have been analyzed, some tentative conclusions can be gleaned from first- and second-year data.

For one thing, yields were higher for both lettuce and spinach crops planted in October, as compared with the crops planted in November. This was attributed to the longer days and warmer temperatures during the October crop’s germination period.

In terms of which model hoop house makes sense for which climate zones, the preliminary report suggests that while the high-end version with two layers of plastic and the heat-conserving barrels kept the inside temperature closer to the optimum for production of these crops, the total production at the Leyendecker site was actually higher in the double-layer hoop houses without the barrels.

As with much NMSU research, this project is expected to offer benefits on many levels. The researchers are breaking new ground with the help of their students, for whom it is a great learning experience. The collaborating producers are not only learning as they go; Uchanski reports that some are also growing other vegetables, including bell peppers and radishes, during the rest of the year.

And the state’s economy stands to benefit in the long run, as the results of the study help other producers increase their production by incorporating the optimal hoop house into their operations.