Winter Production of Leafy Greens in the Southwestern USA using High Tunnels

Winter Production of Leafy Greens in the Southwestern USA using High Tunnels

Summary

In much of the Southwest most winter days are sunny, but nights can fall below freezing. Therefore, passive-solar high tunnels (synonym: hoop houses) should be ideally suited to this region. We are evaluating high tunnels across different climatic zones for their potential to profitably produce winter greens. Lettuce and spinach were planted on October 28 or 29 and November 15 or 18/19 at two experiment stations in New Mexico (NM); one station reflecting a northern location and the other a southern location. Lettuce and spinach were also planted at on-farm study sites in Arizona (AZ), Colorado (CO) and NM. Participants from on-farm study sites have provided experiential information about the use of high tunnels for winter production. Yields and tunnel temperatures were collected in all operational tunnels during year one (2009/2010) and year two (2010/2011). Data collection and analyses will continue for one more winter season (2011-2012).

Objectives/Performance Targets

A) To quantify the differences between three passive-solar high tunnel designs of different expense and heat-retention capacities to assess their potential to provide a suitable environment for winter production of leafy greens.

B) To evaluate growth and yield of one spinach and one lettuce cultivar at two planting dates within each tunnel.

C) To conduct economic analyses to determine relative profitability of each tunnel design.

D) To distribute results and recommendations to farmers, researchers, extension educators and other agriculture personnel in NM, CO and AZ.

Accomplishments/Milestones

Eighteen high tunnels or “hoop houses” were constructed in 2009: seven near Las Cruces, NM, one near Tijeras, NM, six at Alcalde, NM, one near Window Rock, AZ, one at Dine College, AZ, and two near Durango, CO. Hoop house construction workshops were held at these sites and were open to the public. These workshops were led by Del Jimenez and organized in cooperation with county agents, other project PIs and cooperators and provided attendees with hands-on experience in constructing 16×32-foot hoop houses. The hoop houses at Window Rock, AZ, and at Tijeras, NM, were seriously damaged in 2009-2010 due to heavy snowfall during the winter. These two houses were repaired in 2010 and slightly modified to better withstand snowfall, including an outer layer of snow shedding plastic and internal frame reinforcements. Cooperating producers continued experimenting with planting dates and plant varieties as encouraged in the grant proposal. Temperature probes and data loggers were installed in all locations in 2010. A presentation of the hoop house study’s preliminary findings was also given at the New Mexico Organic Farming Conference in Albuquerque in February 2011.

A Master of Science student in New Mexico State University’s Department of Plant and Environmental Sciences, Juliette Enfield, has compiled the harvest and temperature data over the past two seasons and has begun the environmental and biological analysis (temperature, light, yield, plant growth, etc.) for all sites. During the construction of the hoop houses, materials costs and labor inputs were recorded. These data, in addition to maintenance costs and harvest yields, will be used for a full economic analysis as part of Emmanuel Hecher’s graduate studies at NMSU. Mr. Hecher, a Master of Science student in the Agricultural Economics Department, is also working closely with the cooperating producers on the project to gather survey information about the economic uses of their hoop houses.

For objective A of this study, the differences between the three designs of hoop houses are being examined for their potential to provide a suitable environment for leafy greens during the coldest months of the year. There are two replicated study locations, Alcalde, NM, and Las Cruces, NM. Each study location has a total of six hoop houses with two of each design. The three designs include a single layer of plastic (SL), a double layer of plastic (DL) and a double layer of plastic with water barrels (DL+B). Preliminary temperature data analysis shows that each hoop house model has a different temperature regime as seen in Figures 1 and 2. The DL+B house had a maximum and minimum temperature range that was closer to the optimum temperature for lettuce growth than the other hoop house models. During the coldest part of the day, the DL+B hoop house was, on average, about 10 degrees Fahrenheit warmer than the single layer hoop house. The thermal mass of the water barrels in this model buffers the temperature extremes in the hoop house by slowing temperate change. This effect was seen at both experiment locations (Alcalde and Las Cruces). However, the DL+B hoop houses did not have the highest yields as seen in figures 3 and 4. This result was unexpected and is currently being investigated. Due to low yields in the first season of the project, especially for lettuce and spinach planted in December, an earlier planting date was used this season. This earlier planting date allowed the seeds to germinate and develop faster during longer days and slightly warmer temperatures. As seen in figures 3 and 4, the lettuce and spinach that were planted in October yielded more than the crop planted in November. Harvest was terminated when the crop quality declined due to temperature and maturity of the plants (late February 2011).

Many producers planted at different dates than specified and included site specific crops that will be included in economic analysis. The producer near Window Rock, AZ, and all other collaborating producers had a DL model hoop house. The DL model hoop house retains heat well during the day, but the air temperature at night only stays slightly warmer than outside temperatures (Figure 6). Future hoop house models will require a venting system to avoid the high temperatures that are far from the optimum growth temperature range. The temperature differential during the day is quite large for the outside vs. inside temperatures, which is expected on a sunny day. The continued challenge is to keep that heat during the night when these temperatures come back together again. The use of row cover in the hoop house as a protective covering for the crop raised the minimum temperature inside the hoop house on average five degrees (Figure 7). During the particularly cold event in early February 2011, the outside temperature at Window Rock was -10F (lethal for lettuce and spinach in most situations), inside the hoop house was 0F, and under the row cover was +15F, a 25 degree difference (Figures 6 and 7). The producer in Window Rock, AZ, also noted that the soil retained more moisture if the row cover was doubled in thickness when applied over the crop. We will continue to solicit producer inputs and observations in season three.

• Figure 2. Maximum and minimum air temperatures inside three different models of hoop house (SL, DL, DL+B) in Las Cruces, NM, during an unusual temperature drop in early February (2010-2011). Temperatures are average of 2 replications for each model of hoop house.
• Figure 5. Total season long crop yields from ‘Trout’s Back’ lettuce planted in October and in November in three different models of hoop house (SL, DL, DL+B) in Las Cruces, NM. Yields are combined 180 feet of row for each crop.
• Figure 3. Maximum and minimum air temperatures inside three different models of hoop house (SL, DL, DL+B) in Alcalde, NM, during the winter growing season (2010-2011). Temperatures are average of 2 replications for each model of hoop house.
• Figure 7. Comparison of daily high and low air temperatures inside the hoop house vs. inside the hoop house under row cover in Window Rock, AZ, during the winter growing season (2010-2011).
• Figure 1. Maximum and minimum air temperatures inside three different models of hoop house (SL, DL, DL+B) in Las Cruces, NM, during the winter growing season (2010-2011). Temperatures are average of 2 replications for each model of hoop house.
• Figure 4. Total season long crop yields from ‘Bloomsdale’ spinach planted in October and in November in three different models of hoop house (SL, DL, DL+B) in Las Cruces, NM. Yields are combined 180 feet of row for each crop.
• Figure 6. Comparison of daily high and low air temperatures inside vs. outside the hoop house in Window Rock, AZ, during the winter growing season (2010-2011).

Impacts and Contributions/Outcomes

Through the high tunnel construction workshops carried out across New Mexico, northeast Arizona and southwest Colorado, currently more than 200 individuals received hands-on training regarding assembly of high tunnels made of wood, PVC and plastic. General parts-lists and costs were made available, as well as information on other factors to consider (essential tools, etc.) when building their own high tunnel or hoop house. These materials lists will be used in the economic analysis to determine whether the marginal costs of the additional materials in the DL and the DL+B designs are justified by the marginal revenues from increased yields. We will also determine the economic impact of planting date for each crop.

The hoop house projects at both Alcalde and Las Cruces, NM, have been the subject of numerous tours to visitors, scientists, school groups and legislators. Presentation of the project took place at the 2010 Field Day of the Alcalde Science Center, which occurred on August 11, 2010 (attendance registration was 236). The press release announcing this field day also highlighted and discussed the winter greens project. Since the beginning of 2010, the project has been presented to over 14 groups and several individuals who visited the Alcalde Science Center.

The two graduate students have begun writing masters theses for this project. One thesis will undertake a partial budget analysis of the three hoop house designs by planting date and by crop at both experimental sites, and the other will be a horticultural study on the use of hoop houses for lettuce and spinach production during the winter in the southwest. Manuscripts from these masters theses will be submitted to scientific journals to be published and shared among the scientific community. Through project collaboration with County Extension offices in the southwest (Rio Arriba, Do&a Ana, Tri-State Navajo Nation, Bernalillo, La Plata), the results of the hoop house trials will be shared with farmers through workshops and additional publications.

A major impact during the second year of this project has been sharing preliminary study results with farmers. A 1.5-hour presentation was made at the New Mexico Organic Farming Conference in Albuquerque, NM, on February 19, 2011. The presentation provided a forum to introduce the research and share preliminary data with the southwest organic farming community. There was significant attendance and interest in the use of hoop houses for season extension and winter production.

A desired long-term outcome of this project is that a significant number of producers in the southwest region will be engaged in winter greens production. This production may begin to satisfy market potential and serve as a catalyst for new contracts, leading to greater diversity and profitability in agriculture. In addition, consumers in the region may have additional access to fresh local produce for most or all of the year.

• Figure 8. Emmanuel Hecher collecting replicated harvest data in Las Cruces, NM, February 2011.
• Figure 9. Collaborating producer Ian Chamberlain, in his hoop house in Durango, CO, January 2011.

Collaborators: