The 2012 ASHS Annual Conference

Replicated yield and temperature data from passively heated high tunnels (hereafter “houses”) is lacking, especially in the southwestern US. Field studies were conducted over three seasons (2009–2012) in two locations in New Mexico (NM): a southern site in Las Cruces and a northern site in Alcalde to compare three house models for production of leafy greens during the winter (Dec.–Mar.). Houses were 4.9 m x 9.8 m and oriented with the long edge running east to west. Heavyweight woven plastic (SOLAROOF 172, J&M Industries; Ponchatoula, LA) covered the single layer (SL) model. Double layer models (DL) were covered with a lightweight woven plastic (SOLAROOF 140), followed by a second layer of heavyweight plastic (SOLAROOF 172) inflated with a fan. A heat sink was created using sixteen, 208L barrels painted black, filled with water, and aligned on the north side of the double layer with barrels (DL+B) model. Soil temperature (7.6 cm deep) and air temperature (30.5 cm above the soil surface) were recorded in six locations near each house (inside the house, inside the house under a floating row cover, and outside the house). Yields of ‘Bloomsdale’ spinach and ‘Flashy Trout’s Back’ lettuce from two planting dates (28 Oct. and 18 Nov.) were evaluated. Data collection included plant height, fresh weight, dry weight, and stand count at each harvest. At the first harvest in the 2009–2010 season in Alcalde, lettuce yield from the November planting was significantly higher in the DL+B model than the SL model. However, in both season one and two, there were no statistical differences between the SL and DL+B models for total, season-long lettuce yields. In the month of January, the mean minimum air temperature inside the SL model was 3°C warmer than outside. Daily air temperature minimums were highest in the DL+B, followed by the DL, and SL models (2.2°C, –1.1 °C, and –3.9 °C, respectively). Throughout the growing season, the DL+B and SL models had comparable maximum daily air temperatures (26.7°C and 26.1°C, respectively) due to the buffering effect of the heat sink. Row covers (Agribon AG-19, J&M Industries) also had an impact on air temperatures. Minimum air temperature under the row cover and inside the SL house at Alcalde was an average of 6°C warmer than the air temperature inside the house, but not under row cover. Data collected in this study can help inform the decisions of high tunnel growers and researchers.