Often called hoop houses, high tunnels are constructed by stretching a layer of polyethylene plastic over hoops of metal or polyvinyl chloride (PVC). Most high tunnels rely on passive ventilation through roll-up sides, large doors, or removable end walls. High tunnels are less-complex, less-expensive versions of a greenhouse because of passive heating and cooling and inexpensive glazing. They can offer growers a cost-effective way to extend the growing season for high-value crops such as fruits, vegetables, and cut flowers. High tunnels also allow small farmers to gain market share in the niche market of “locally grown” products at a time of the year when most fruits and vegetables are grown elsewhere.
Extending the vegetable production season without incurring prohibitive costs is an important goal of many farmers, especially small and beginning farmers with limited resources. Extending the season with high tunnels allows for a more-constant income flow and some control of the crop growth environment. High tunnels can provide protection against some insects, early freezes, hail, and other weather events. High tunnels can also facilitate better market planning. Season extension technologies alter the growing environment equivalent to moving three U.S. Department of Agriculture Plant Hardiness Zones to the south, which makes production of spinach and lettuce in cold winter weather possible (Coleman, 2009; Wells and Loy, 1993).
Although high tunnels have been extensively studied in the eastern and midwestern parts of the United States, little work has focused on the southwestern part of the country. With limited water and a dry climate, farmers in the southwestern United States are under pressure to divert agricultural land and water to residential and other nonagricultural uses (Hurd and Coonrod, 2008). At the same time, new marketing opportunities are developing that encourage schools and other public institutions to purchase fresh produce from local farmers. To take advantage of these opportunities and deal with these challenges, farmers need to be able to supply fresh produce in a cost-effective manner during the late fall, winter, and early spring months. In most of the southwestern United States, the majority of winter days are sunny, but nights (and in some areas, days) are below freezing. Low-cost, passive-solar high tunnels seem to be an ideal fit for farmers in this region. In recent years, New Mexico agricultural producers have adopted high tunnel technology, but detailed production and economics data are lacking. Stakeholders need additional information about winter vegetable production in high tunnels.
High tunnels are generally tall enough to walk in, whereas low tunnels are designed to cover the crop itself and are typically 1 to 2 ft tall. Low tunnel technology has been explored as one form of extending the crop season in southern New Mexico. Ma (2009) examined the economic impact of using low tunnels to extend the season for four lettuce and four spinach cultivars. For lettuce, low tunnels improved yields as much as 23% in the fall, whereas, in the spring, those improvements were as high as 70% when compared with the control. Spinach also performed well, with yields 68% higher in the fall and 66% higher in the spring when compared with the control (Ma, 2009). A partial budget analysis was used to evaluate the economic performance of the low tunnels. A price of $4/lb was used, based on previous sales of lettuce and spinach in the area. In Fall 2008, rowcovers had a positive economic effect on only one cultivar of lettuce, with a cumulative impact of $1170/acre over three harvests. All other lettuce and spinach cultivars in the fall had a negative economic effect under rowcovers. In the spring, rowcovers had positive economic effects on all lettuce and spinach cultivars, with the highest cumulative returns from three harvests of $36,388/acre for one lettuce cultivar. A spinach cultivar had the highest returns of $46,123/acre from four harvests. However, high tunnels have increasingly been adopted in New Mexico due to the labor involved in managing and maintaining low tunnels.
In the northern parts of the United States and Canada, high tunnels present several advantages, such as allowing the crop to be planted as much as a month earlier and protecting against rain and wind, resulting in a higher quality product (Wien, 2009). Growers surveyed in Missouri, Kansas, Nebraska, and Iowa reported extending their season to 9 months of the year using high tunnels and 91% reported growing tomatoes (Solanum lycopersicum) in high tunnels (Knewtson et al., 2010). Other crops reported were lettuce, spinach, leafy greens, cucumbers (Cucumis sativus), and peppers (Capsicum sp.). Internationally, the most commonly produced crop in high tunnels is tomato, followed by pepper, cucumber, muskmelon (Cucumis melo var. reticulatus), and lettuce (Knewtson et al., 2010).
In Michigan, nine case studies were used to analyze the viability of high tunnel vegetable production (Conner et al., 2010). The materials cost roughly $10,000 for a tunnel of ≈2800 ft2 (Conner et al., 2010). Net payback was an estimated 4.2 years, assuming the entire net mean monthly income of $201 was used to pay for the investment (Conner et al., 2010). Waterer (2003) evaluated the economics of summer vegetable production in high tunnels and low tunnels in Canada. Crops in high tunnels matured earlier and produced higher yields before a killing frost, but did not effectively extend the growing season. High tunnels required much higher initial investment, but enhanced gross returns on the wholesale market allowed for a 2- to 5-year payback period. Economics information is available for other parts of the United States and Canada but is limited for growers in the southwestern United States.
Risk and uncertainty are part of any business, including agricultural investments. Although capital investment costs may be easy to estimate, yields and prices received in the market are variables over which farmers have limited control. These variables can greatly influence the decisions of small growers who have constrained budgets. Developing a model, that takes risk into account, is important to improve investment decisions. Therefore, it is also important for vegetable growers to understand their probabilities of covering material and seed costs before investing.
@Risk™ statistical software (Palisade Corp., Ithaca, NY) has been widely used to make financial decisions by examining uncertainty. The software has been used in the financial industry for retirement planning, currency valuation, portfolio optimization, and discounted cash flow analysis (Togo, 2004). It is used in the insurance industry in estimating loss reserves. @Risk™ is also used in the energy industry to determine oil reserves estimation, exploration, and production. Yeboah et al. (2012) used @Risk™ to examine the economic feasibility of a North Carolina biodiesel plant that used canola (Brassica rapa) seeds as the primary feedstock. The software has also been used in agricultural investment decision projects (Tzouramani and Mattas, 2004). BestFit is a feature of @Risk™ that identifies the distribution that best fits the input data (Jankauskas and McLafferty, 1996). In combination with simulation software, these distributions can be used to define uncertainty in the model.
This project evaluated three models of high tunnels for winter production of leafy greens over three seasons. The emphasis was on low-cost, practical structures that are applicable to farmers with limited resources and who may wish to test winter production before making larger investments in more advanced greenhouse technology or transitioning to larger units. Specific objectives were to 1) quantify the differences between three passive solar high tunnel designs of different expense and heat-retention capacities, 2) evaluate growth and yield of one spinach cultivar (Long Standing Bloomsdale) and one lettuce cultivar (Flashy Trout’s Back) at two planting dates within each tunnel, and 3) conduct economic analyses using novel software to develop a risk model to determine relative probability of profitability of each tunnel design.
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