This study tested various perforated plastic materials (clear and white) used as low tunnels either alone or in combination with a spun-bond material for benefits including: frost protection, earliness in planting and harvesting, and season extension. The experiment consisted of six treatments: Four combinations of clear and white plastic with or without the spun-bond materials and two controls with no covers (normal planting date in May and early planting date in April). Using slicing cucumber and tomato, the low tunnels were investigated for their impact on the microclimate, crop earliness and economics. Our preliminary studies showed that by combining perforated clear plastic and spun-bond material together in a low tunnel system, air temperature during frost events can be increased significantly inside the tunnels.
For many centuries horticulturists have been challenged by the limitations imposed by climate on crop production (Well and Loy, 1985). Horticulturists today are facing the same challenges, especially in areas with a temperate climate like Michigan. Since the 16th century, many have attempted to modify the environment to enhanced frost protection and crop growth (Janick, 1979).
Row covers or low tunnels can modify climate by preventing frost damage and promoting earlier plant growth (Hochmuth, et al. 2009). By using plastic mulch together with low tunnels, soil temperatures can be increased, weeds can be controlled, water can be conserved, and fertilizer application is optimized (Schrader, 2000). Plastic mulches used for row covers are available in different colors, which impact the light quality and temperatures inside the tunnels. However, it is not known which low tunnel color, type, or configuration will provide the most protection in temperate climates.
Michigan’s commercial production of fresh marketable vegetables is worth over $175.9 million in sales and covers about 49,200 acres (USDA, 2013). The Michigan slicing cucumber industry is valued at $14.4 million annually and the crop is produced on 3,600 acres, and the tomato industry is valued at $16 million annually with 2,000 acres. Both crops contribute significantly to the state economy.
Both cucumber and tomato growers do not take advantage of the full potential of their crops for several reasons including the following: (1) the growing season is short because of the limitations imposed by the temperate climate; (2) most of the crop is planted and harvested within a short window of time, resulting in peaks in harvest that routinely lead to low prices; (3) the potential of frost damage is a significant risk for growers who might want to plant earlier to avoid harvesting in the peak period; and (4) alternative methods for on-farm season extension are limited. If growers can successfully modify climate they will be able to plant and harvest earlier and command higher prices for their crops at the beginning of the season. Low tunnels are a strategy that growers can use in open field to limit the risk of frost damage, thereby allowing them to plant and harvest earlier.
By creating new cropping systems that overcome climate limitations, Michigan’s commercial fresh market production can grow and bring more revenue to the state. Therefore, this study was designed to estimate the costs and benefits of various low tunnels for cucumber and tomato production under Michigan conditions. We analyzed the profitability of using different low tunnel configurations that modify climate and compared their costs to those of standard field practices using plasticulture system in Michigan.
Objective 1. Develop and validate new low tunnel technologies.
Objective 2. Conduct an economic analysis of the production systems.
Objective 3. Deliver information to growers and the scientific community.
Experimental Site and Procedures
The research was conducted at the Southwest Michigan Research and Extension Center (SWMREC) at Benton Harbor, Michigan, in cooperation with a local grower, who participated in low tunnel installation and monitoring. The 1-mil embossed plastic mulch and plastic drip tape were laid on 5 ft (1.5 m) (center to center) wide beds and 50 ft (15.25 m) long, which were prepared with a plastic mulcher attached to a tractor. Slicing cucumber and fresh market tomato were used as model crops in the experiment. ‘Mountain Spring’ tomato transplants were set in place 20 in (50.8 cm) apart with 28 experimental plants per treatment. ‘Mariana’ tomatoes were used as guard plants at the start and end of each tomato plot and in the two outermost guard rows. ‘Speedway’ cucumber was direct-seeded, two seeds per hole, with the same spacing as the tomato, totally 60 experimental plants. Experimental plots were arranged in a randomized complete block design with three replications and oriented so tomatoes were in the northern half of each treatment and cucumber was in the southern half of each treatment. In the early planting date treatments tomato transplants and cucumber seeds were planted on April 26, 2011 and April 24, 2012. The no row covers standard system normal planting date plots were planted on May 27, 2011 and May 24, 2012 for cucumber and tomato, respectively.
The experiment consisted of six treatments: 1. No row covers-standard system with normal planting date in May (NCN); 2. No row covers-standard system with early planting date in April (NCE); 3. Single layer: clear polyethylene plastic row covers (CS); 4. Single layer: white polyethylene plastic row covers (WS); 5. Dual layer: clear polyethylene plastic and spun-bond polypropylene row covers (CD); and 6. Dual layer: white polyethylene plastic and spun-bond polypropylene row covers (WD). The NCE treatment was included for scientific reasons only since no grower in the region would risk planting unprotected tomato or cucumber in April.Dual layer treatments included a small band of 30 in (76 cm) wide spun-bond material placed inside the tunnels, sandwiched between the hoops, in addition to the normal low tunnel plastic (Figure 1). A special implement designed by the cooperating grower was used to simultaneously lay the two materials. The clear and white polyethylene plastics were perforated for appropriate ventilation especially on hot and sunny days.
Low tunnels were installed immediately following crop planting. Planting holes were punched through the black plastic mulch on the raised beds using a tractor mounted hole-punching wheel. Immediately after planting tomato or seeding cucumber, 62 in (1.6 m) spring steel wires were manually installed. Then the 1-mil, (weight 65#) 6 ft (1.8 m) wide perforated tunnel plastic and the spun-bond plastic were laid over the wires and their edges were mechanically covered with soil around the periphery of each plot. The tomato low tunnels were vented prior to tunnel removal to let the plants acclimate. Low tunnels were removed manually at the end of May, when the tomato plants were touching the top of the plastic and the threat of frost was past. Tomato plants were pruned by hand, leaving the first sucker below the first flower cluster and removing all suckers below it. Field activities and pesticide applications followed standard grower practices, except in 2012 when bacterial symptoms appeared on June 25. The dates of key field activites are summarized in Table 1.
Soil temperature was recorded with a WatchDog B101 8K Temp Logger (Spectrum Technologies, Inc., 12360 South Industrial Drive East, Plainfield, IL) at a depth of 4 inches (10 cm) in each treatment. Air temperature and relative humidity were recorded with a WatchDog B1-2 Temp/RH Logger (Spectrum Technologies, Inc.) at a height of 6 inches (15 cm) above the bed in each treatment with the logger facing north. Photosynthetically active radiation (PAR) was recorded with a WatchDog 1000 Series Logger connected to a LightScout Quantum Light Sensor (Spectrum Technologies, Inc.) at a height of 10 inches (25 cm) in replication two. The data loggers and sensors were placed on a stake (Figure 1) at the center of each tomato treatment. Sensor data were collected every 30 min starting at 6 pm on the day the low tunnels were installed until the low tunnels were completely removed.
Height of every other plant was measured every 2 wk in all treatments in both years, starting from the day of low tunnel removal until the first cucumber harvest. Frost damage was assessed by taking a stand count after the low tunnels had been removed. Cucumber leaves and tomato flowers were counted after the low tunnels had been removed. The 24th and 28th tomato plant were sampled for growth analysis (branch count, fresh and dry weight, and leaf area measurements). All branches with more than one fully expanded leaf were counted. The area of all the leaves was measured by a LI-3100 Area Meter (LI-COR Environmental, 4647 Superior Street, P.O. Box 4425, Lincoln, NE). The counts and measurements were also obtained from the normal planting date treatments.
Tomatoes were harvested eight times from the early planted treatments in 2011 and nine times in 2012, while the late planted treatments were harvested seven times in 2011 and 2012. Harvest took place once or twice per week. Tomatoes were separated into Grade 1 Large (US No.1), Grade 1 Small (US No.1), Grade 2 (US No. 2), and cull (Unclassified) (USDA-AMS 1991). The fruit within each grade and from each treatment were counted and weighed. On the last harvest date all fruit were separated into mature fruit (red or pink color at the blossom end) and green fruit. Plants were destructively harvested and fresh above-ground biomass was weighed.
Cucumbers were harvested 16 times from the early planted treatments and 11 times from the late planted treatments in 2011, and 13 times for the early planted treatments and 9 from the late planted treatments in 2012. Harvest took place twice per week. Cucumbers were separated in to Grade 1(US No. 1), Grade 2 (US No. 2), and cull (Unclassified) (USDA-AMS 1958). The fruit within each grade and from each treatment were counted and weighed.
The experiment was conducted in 2011 and 2012, followed by final data analysis and dissemination of results.
All low tunnel configurations provided 1-7 oF of frost protection compared to the ambient temperature in the no cover early planting date (NCE) treatment and resulted in significant heat accumulation at the beginning of the growing season (Figures 2 and 3).
There were two frost events in 2011 that occurred on May 5th and 16th. Frost damage in the NCE treatment was evident in the field, since frost damaged plants were set back compared to the covered plants (Figure 4).
The low tunnel treatments for cucumber were first harvested on June 27, 2011, while the no cover normal (NCN) planting date crop was first harvested on July 14, 2011, representing more than two weeks of earliness. The cucumber clear dual layer (CD) treatment had the greatest yield for the majority of the season; while the clear single layer (CS) treatment was second highest (Figure 5). This result confirmed that the main impact of the row covers was on earliness, which may result in significant economic benefit to the grower, when early harvest prices are higher. Growers who harvest their cucumbers early in the season may also limit losses due to downy mildew-a devastating disease of cucurbits in the region.
The tomatoes in the low tunnel treatments were first harvested on July 19, 2011, while those in the NCN treatment were first harvested on August 1, 2011. In 2011, tomatoes in the CS treatment had the greatest yield throughout most of the season. At the end of the season the greatest difference for overall marketable yields was between the low tunnel treatments and the NCN treatment, which was the lowest (Figure 6). The short growing season is the major yield limitation in the control treatment with no row cover.
Similar to 2011, average air temperatures were increased under all low tunnel configurations compared to the ambient air temperature in the no cover early planting date (NCE) treatment and resulted in significant heat accumulation at the beginning of the growing season (Figure 7).
Under certain conditions air temperatures in low tunnels were lower than the ambient air temperature. One example of such an occurrence took place on April 27, 2012 the only frost event during the growing season (Figure 8). During this event the ambient air temperature was higher in the NCE (open air) treatment compared to all the low tunnel treatments. A similar observation was reported by Wien (2009) on studies using high tunnels.
During the day time hours IR energy produced by the sun increases the temperature within the low tunnels compared to the ambient air temperature, which exceeds the transmittance of the energy leaving the low tunnel back to the outside. Different types of plastics can transmit more or less IR energy depending on its transparency (Wien, 2009). The temperature decrease in the low tunnels below the outside ambient air temperature was likely caused by the property of plastic which transmits infra-red radiation with long wavelength (Baytown, 1994). Therefore, the more IR energy that is lost the lower the temperature with in the low tunnel.
In general, tomatoes are susceptible to chilling injury when exposed to 50 oF or below (Kinet and Peet, 1997). In this case, temperatures were much lower than 50 oF, but tomatoes can also be cold-acclimated by exposure to short periods of low temperature conditions as low as 26.6oF (Hunter,et al. 2012). This explains why some tomatoes were only damaged rather than completely killed (Figure 9).
The low tunnel treatments for cucumber were first harvested on June 25, 2012, while the NCN planting date treatment was not ready for harvest until July 9, 2012. During the 2012 season, yields in the NCN treatments were second highest at the end of the season, because of the lack of frost protection during the unique frost event (Figure 10). This result confirmed that the main impact of the row covers was on earliness, which may result in significant economic benefit to the grower, when early harvest prices are higher.
The tomatoes in the low tunnel treatments were first harvested on July 12, 2012, while those in the NCN treatment were first harvested on July 23, 2012. In 2012, tomato in the WS treatment had the greatest yield for most of the season (Figure 11).
Baytown, N., K. Abak, H. Tokgoz, and O. Altunas.1994. Effect of different greenhouse covering materials on inside climate and on the development of tomato plants. Acta Hort. 366:125–132.
Hochmuth, G.J., Hochmuth, R.C., Kostewicz, S., and Stall, W. 2009. Row Covers for Commercial Vegetable Culture in Florida. Circular 728, Department of Horticultural Sciences, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida.
Hunter, B., D. Drost, B.L. Black, J. Frisby, R. Ward. 2012. Improving growth and productivity of early season high tunnel tomatoes with targeted temperature additions. HortScience 47(6): 733-740.
Janick, J. 1979. Horticulture’s ancient roots. HortScience 14:299-313.
Kinet, J.M. and M.M. Peet. 1997. Tomato. In: Wien, H.C. (ed.). The physiology of vegetable crops. CAB International, New York, NY.
Lamont, W.J., (ed.). 1998. Vegetable production using plasticulture. Proc. Amer. Soc. Hort. Sci. and Amer. Soc. Plasticulture Seminar Series. Alexandria, VA., ASHS Press.
Schrader, W.L., 2000. Plasticulture in California Vegetable Production. Publication 8016, Division of Agriculture and Natural Resources, University of California.
USDA (United States Department of Agriculture). 2013. Michigan Agricultural Statistics 2012-2013. http://www.nass.usda.gov/Statistics_by_State/Michigan/Publications/Annual_Statistical_Bulletin/stats12/vegetables.pdf.
USDA-AMS (United States Dep. Of Agriculture- Agricultural Marketing Service). 1991. Reprint 1997. United States Standards for Grades of Fresh Tomatoes. http://www.ams.usda.gov/AMSv1.0/getfile?dDocName=STELPRDC5050331
USDA-AMS (United States Dep. Of Agriculture- Agricultural Marketing Service). 1958. Reprint 1997. United States Standards for Grades of Cucumbers. http://www.ams.usda.gov/AMSv1.0/getfile?dDocName=STELPRDC5050262
USDA-AMS (United States Dep. Of Agriculture- Agricultural Marketing Service). 2011-2012. Run a Custom Report. http://marketnews.usda.gov/portal/fv?&paf_gear_id=1200002&repType=wiz&paf_dm=full&startIndex=1&dr=1
Wells, O.S. and J.B. Loy. 1985. Intensive vegetable Production with row covers. HortScience 20: 822-826.
Wien, H.C. 2009. Microenvironmental variations within the high tunnel. HortScience 44:235–238.
Educational & Outreach Activities
To date, results from this project have been disseminated to the scientific and grower communities through presentations at the following Conferences:
Oral presentation. Rebekah Struck (Faivor) and Mathieu Ngouajio. 2010. Low Tunnel Cucumber and Tomato Production. Great Lakes Fruit, Vegetable, and Farm Market Expo, Grand Rapids, MI.
Poster. Rebekah Faivor and Mathieu Ngouajio. 2011. Low Tunnel Strategies for Microclimate Modification and Early Vegetable Production. Great Lakes Fruit, Vegetable, and Farm Market Expo, Grand Rapids, MI.
Poster. Rebekah Faivor and Mathieu Ngouajio. 2011. Low Tunnel Strategies for Microclimate Modification and Early Vegetable Production. American Society of Horticultural Science (ASHS) Annual Meeting, Waikoloa, HI.
Oral presentation. Rebekah Faivor and Mathieu Ngouajio. 2012. Low Tunnels for Frost Protection and Earliness. Great Lakes Vegetable Working Meeting, East Lansing, MI.
Oral presentation. Rebekah Faivor. 2014. Low Tunnel Strategies for Microclimate Modification and Early Vegetable Production. OEFFA & NCR-SARE Farmers Forum, Granville, OH. https://youtu.be/0aYThz7b828
Thesis: Faivor, R.M.S. 2014. Low Tunnel Strategies for Microclimate Modification and Early Vegetable Production. M.S. Thesis. Michigan State University. In Progress.
This study has showed several positive results/outcomes of using low tunnels:
Tomatoes and cucumbers planted under low tunnels can successfully be planted one month prior to the last frost date in Michigan.
Low tunnels accumulate up to twice as many growing degree days.
Tomatoes and cucumbers can be harvested up to two weeks sooner than a typical harvest time in Michigan under low tunnels.
Low tunnel tomatoes in this study were produced before Michigan tomatoes were available at the Detroit Terminal.
The data on inputs costs, crop yield, and market prices were used to determine the most profitable low tunnel configuration that promoted the best economic return using a partial budget analysis.
The additional costs beyond those of a standard tomato or cucumber field planting were calculated based on pricing and the experience of the grower cooperator, who is a local grower who tested the low tunnel production system developed in this study. The low tunnel layer machine was built by this grower, George McManus, and was modified to lay two layers simultaneously, while wires to support the tunnel layers were manually installed. The estimated cost of the unit was $3,500. Assuming that this machine lasts 5 years and covers 100 acres per year the cost is $7 per acre to use the machine. Most growers consider renting machinery rather than purchasing it new, since the cost of maintenance or purchasing can be high. Labor costs for the low tunnel treatments were estimated at: $75 per acre for wire installation, $63 per acre for low tunnel installation, $75 for low tunnel removal, and $25 per acre for wire removal, which totals $238 per acre. Equipment and labor costs were the same for all low tunnel treatments, totaling $245 per acre.
The NCN and NCE treatments required no inputs beyond the standard production practices. The CS treatment material costs were $ 298 per acre for the low tunnel clear plastic and $6.50 per acre for the wire. The CD treatment material costs add $138 per acre for the spun-bond material. The WS treatment material costs were $305 per acre for the low tunnel white plastic and $6.50 per acre for the wire. The WD treatment material costs add $138 for the spun-bond material. Equipment, labor, and material costs specific to each treatment were added to the standard production cost. All additional cost associated with the low tunnels are indicated in Table 2 and include, plastic mulch, spun-bond material, wire hoops, tractor use, labor for low tunnel installation, ventilation, and removal. All other regular inputs (land preparation, planting, crop maintenance, harvest and handling) were similar across treatments and; therefore not included in the partial budget analysis.
Yields for each treatment were based on data from the field experiments performed 2011 to 2012 at SWMREC. All marketable fruit yields were from a 50 ft row on 5 ft centers. The selling units for tomatoes and cucumbers at the Detroit Terminal are 25 lb carton and 1 1/9 bushels, respectively (Table 3 & 4). Therefore, yields in individual plots were converted to those units to facilitate the economic analysis.
For each week of harvest we tracked the market price of cucumber and tomato at the Detroit Market Terminal during the 2011-2012 growing seasons using the USDA Market News website (USDA-AMS, 2011-2012). Prices drop in mid-season, which is the peak harvest time for cucumbers and tomatoes (and other vegetables). These data are provided by the USDA and are based on prices received by wholesalers who sell less than a car or truck load of produce. Tomatoes and cucumbers are offered at the Detroit Terminal year-round, but Michigan field-grown tomatoes and cucumbers are available only for a short time. When Michigan produce prices were not available, prices were estimated based on data published from other states. An average was taken of the ‘high’ and ‘low’ prices for the week to calculate the weekly price of tomatoes (vine-ripened fruit in 25-lb carton loose packaging) and cucumbers (medium-sized fruit in 1 1/9 bushel cartons)(Table 3 & 4). These prices did not include transport or labor costs.
Revenue and Profitability
Pounds of tomatoes or bushels of cucumbers obtained from each treatment were totaled for each week of harvest and assigned a wholesale price for that week. To obtain a gross revenue estimate, weekly revenues were added for each season and the costs of equipment, labor, and materials were subtracted from seasonal revenues (Table 5).
A partial budget analysis was done that did not take into account other regular inputs. The net revenue is not what a grower will get but instead gives an idea on the benefits resulting from the use of low tunnels. Figure 12 shows the control no cover treatments in the orange and dark blue (the bars on the far left and far right of each crop shown in the graph) had the least amount of revenue compared to the low tunnel treatments in 2011. When prices are high at the beginning of the season and adequate frost protection is provided by the low tunnels they are beneficial.
This project showed vegetable growers the potential benefits, risks, and costs of using different materials for laying low tunnels. In particular, farmers exposed to this research should have a better understanding of how different color plastics with or without a row cover can benefit two different field crops. This project can easily be adopted by farmers with or without low tunnel laying equipment depending on the scale of their production. Farmers with larger scale farms can purchase the Model 95 Low Tunnel Layer made by Mechanical Transplanter, which similar to the low tunnel layer machine used in this project. There are a few differences between these machines. The Model 95 sets the wires mechanically rather than by hand, which could reduce labor costs. This machine would need to be modified to lay two different low tunnel materials simultaneously to minimize frost risks. Farmers looking to just try this short term could lay low tunnels by hand or rent equipment.
Areas needing additional study
In order to get the most out of low tunnel vegetable production, there is still much to learn about low tunnel timing, color, fabric, size, and practicality, along with how different vegetable varieties respond to these factors. This research has raised some of the following questions:
What time frames could low tunnels be used?
Low tunnels were installed the last week of April for this project. Depending on the crop being planted low tunnels could be installed earlier depending on how cold tolerate the variety.
What other crops besides cucumbers and tomatoes benefit from the use of low tunnels? Preliminary studies show that watermelon, cantaloupe, buttercup squash, summer squash, eggplant, habanero peppers, and jalapenos peppers can produce up to two weeks earlier when planted under low tunnels. Crops such as habanero peppers and pumpkins that need over 100 days of maturity will have 14 more days to complete their growth period when grown under low tunnels. Heat accumulation could be too intense for cool weather crops, such as lettuces and brassicas, but there could be a possibility of using other low tunnel materials or row covers that do not capture so much heat.
How do different colors (other than white and clear) of low tunnel plastic affect light quality and heat accumulation?
There are many options for different colors of plastic mulch, which can benefit yields in various vegetable crops.
Would removable low tunnels be more beneficial than stationary one time use low tunnels?
While the wires in this project were reusable, the plastic and fabric in this project were one time use. If materials were able to be used for multiple years, the cost of materials would be reduced.
Does tunnel length or width matter?
In this project, 62 in long wires and 6 ft wide plastic was used to make the tunnels. The Model 95 Tunnel Layer comes in three different sizes, narrow, standard, and wide. Tunnel lengths were approximately 50 ft long. If tunnels were longer would more heat be accumulated?