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  • Author or Editor: Juliette Enfield x
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Relatively little season extension research has been conducted in the southwestern United States, particularly with low-cost high tunnels or hoop houses for small-scale farmers. In this study, the economics of winter production of two leafy crops [lettuce (Lactuca sativa) and spinach (Spinacia oleracea)] in high tunnels in two locations in New Mexico were investigated, first using a simulation analysis in which yields were stochastic variables followed by a sensitivity analysis to examine returns from the high tunnel designs more closely. The returns examined in the sensitivity analysis were net of high tunnel materials, crop seed cost, and electricity. Two planting dates were tested and three high tunnel designs were examined: a single layer covering the house (SL), a double layer inflated with air (DL), and a double layer inflated with air and containing black water barrels to store heat (DL+B). The SL and DL designs appear to be the more appropriate technology for both locations for spinach, whereas for lettuce the DL+B model might be a reasonable option in Alcalde, a more-northern location. Overall, the SL and DL models provided adequate protection for growing crops, were less expensive to build, provided more interior growing space, and resulted in higher probabilities of producing positive returns, compared with the DL+B design. The DL design performed similarly to the SL design, but required running electricity to the structure to power the inflation fan, adding to the cost. As a result, expected returns in all cases were higher using the SL design based on the results of the sensitivity analyses. Combining the risk and the sensitivity analyses provides growers with a unique evaluation process to make high tunnel design, planting date, and crop choices.

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Replicated temperature data from passively heated high tunnels are lacking, especially in the southwestern United States. Field studies were conducted over three seasons in two locations in New Mexico—a southern site in Las Cruces and a northern site in Alcalde—to characterize the crop environment in three high-tunnel designs during the winter growing season (October–March). High tunnels were 16 × 32 ft and oriented with the long edge running east to west. Heavyweight woven plastic covered the single-layer (SL) high-tunnel design. Double-layer designs (DL) were covered with a lightweight woven plastic on the bottom, followed by a second layer of the heavyweight plastic inflated with a fan. A heat sink was created using 16 55-gal barrels painted black, filled with water, and aligned along the north side of the double layer for the DL+B design. Soil temperature (3 inches deep) and air temperature (1 ft above the soil surface) were recorded inside the high tunnel, inside the high tunnel under a floating rowcover, and outside the high tunnel. In addition, photosynthetically active radiation (PAR) was recorded inside and outside the high tunnels during or near the winter solstice each year of the study. Daily air and soil temperature minimums were highest in the DL+B design and lowest in the SL design. Maximum air and soil temperatures did not significantly differ between high-tunnel designs, although the DL+B design measurements were consistently lower. During season 1, the SL design had significantly higher PAR transmission than the other two designs. In the northern location, the difference became insignificant during seasons 2 and 3, likely due to dust accumulation and plastic aging. In the southern location, the SL design maintained higher PAR transmission throughout the study, possibly due to plastic cleaning. Data collected in this study can help inform the decisions of high-tunnel growers and researchers in the region.

Open Access