Effects of High Tunnels on Lettuce, Parsley and Ciliantro in the Deep South

Final Report for GS11-103

Project Type: Graduate Student
Funds awarded in 2011: $10,000.00
Projected End Date: 12/31/2011
Grant Recipient: Louisiana State University AgCenter
Region: Southern
State: Louisiana
Graduate Student:
Major Professor:
Dr. Carl Motsenbocker
Louisiana State University AgCenter
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Project Information


Field studies were conducted in the winter of 2012 to evaluate the effects of high tunnels on the growth, yield, and nitrate levels present in the edible portions of parsley (Petroselinum crispum “Giant of Italy”), cilantro (Coriandrum sativum “Calypso”) and a green leaf lettuce (Lactuca sativa “Salad bowl”). High tunnels are used to modify the environment by increasing air and soil temperatures, resulting in higher quality products and total yields when compared to open field grown crops. Cilantro, parsley, and leaf lettuce were transplanted into black plastic mulched beds on 1.22 meter centers with plots 3 meters long either in a high tunnel (HT) or open field (OF) on January 10 and February 10, 2012. The parsley and cilantro transplants were 4 weeks old and the Lettuce was 6 weeks old at the time of planting. The three crops were planted in a split plot design with three replications of each treatment (HT or OF). All plots were mulched with black plastic with drip irrigation installed four cm deep along the center of the raised beds. A main irrigation line was run between the six plots, which then branched to one of six plots. Fertilization followed commercial recommendations with a preplant application of 8-24-24 at 50 lbs./acre (Ammonium sulfate, diammonium phosphate, muriate of potash, triple superphosphate) based on soil test recommendations. Individual height/width and chlorophyll measurements were taken every two weeks and at harvest. At time of harvest, untrimmed harvest weight and trimmed market weight were taken. Dry weights of individual heads were measured after drying in a forced air oven (50ºC). Leaf area, yield and nitrates were measured. Growth and yield in the high tunnel treatment was expected to be greater than in the open field due to the effect of increased soil and air temperatures on growth degree-days (GDD) in the high tunnel. Differences in nitrate levels were expected due to high tunnel/open field treatment.


The purpose of this project is to determine the effects of high tunnels on the growth and potential season extension of profitable crops such as lettuce, parsley and cilantro. According to the 2010 Outlook for Louisiana Agriculture, the majority of commercial vegetable crops sold in Louisiana, are sold through direct marketing at farmers’ markets and roadside stands. Producers can command a higher profit through direct marketing while reducing the risk of selling at a lower price on the wholesale market (L.S.U. AgCenter, 2010). The demand for locally grown produce sold at farmers’ markets has increased dramatically in recent years, increasing by 16% from 2009 to 2010, and tripling from 1755 farmer’s markets in 1994 to 6132 markets in 2010 (USDA AMS- Marketing Services Division 2010 c1). Salad greens are a large seller at many farmers’ markets and the demand is always high. Having them earlier for sale and during unfavorable climatic conditions gives one a competitive advantage. Parsley and cilantro are among the most demanded culinary herbs among restaurants and consumers (Brown, 1991; University of Kentucky Extension, 2010). In the Deep South, these herbs have a relatively short season in the spring. High tunnels could result in an earlier harvest and a longer growing season for all three crops. High tunnels provide a greater amount of control over the growing environment, as well as reduced pest and disease pressure. If lettuce, cilantro, and parsley production in high tunnels generates a higher yield over their field grown counterparts, it could equate to a greater profit margin (U.K. Extension, 2010). High tunnels provide greater control of the growing environment, resulting in reduced fertilizer use and decreased insect and weed pressure (Lamont et.al, 2003; Waterer, 2003; Montri, 2009). This has two main benefits; reducing the amount of fertilizer required and reduced pesticide use and application. Because less fertilizer is required, the high tunnel crops should have lower nitrate content at harvest and reduced soil leaching. Vegetables are consumed because of their reported and assumed health benefits. Nitrates can pose a threat to human health in high levels. Plants absorb nitrogen in the form of nitrate, and it is found in higher concentration in leaf, root, and tuber than in fruit, seed, and bulb vegetables (Gonzales et al., 2010). Issues with nitrate toxicity are minimal, but the compounds derived from nitrate reduction, nitrosamines and nitroamides, have carcinogenic effects (Santamaria et.al., 1999). By monitoring the effects of nitrate content in high tunnel versus open field, potential health impacts can also be observed. Fewer applications of pesticides would reduce money spent on inputs as well as application labor. Lower pesticide use could also lower negative effects on beneficials.

Project Objectives:
  1. 1. Analyses of nitrate, chlorophyll, plant height, fresh and dry weights, leaf area, light quality, and temperature variation to investigate the influence of the growing environments on nitrate levels as well as overall nutrient uptake (Gent 2002; Yi et al., 2010).
    2. Determine the difference in growth degree days between high tunnel/open field treatments.
    3. Determine financial differences of high tunnel vs. open field treatment on the specified crops. Determine effect of HT treatment vs. open field on yield of specified crops.


Click linked name(s) to expand
  • Dr. Carl Motsenbocker


Materials and methods:

The study was conducted at the Burden Center in Baton Rouge, LA. The soil type is Oprairie silt (30° 24′ 27.6114″, -91° 6′ 43.4268″) (websoilsurvey.nrcs.usda.gov). Test plots were set up in a split plot design with three replications in high tunnels (HT) and three open field (OF) plots. The main treatment was the HT or OF treatment and the sub-treatment was the crop planted and planting date. Three ClearSpan™ Gothic style cold frame high tunnels, measuring 20′ W x 12′ H x 36′ L, were used for the trial. The high tunnels were constructed on-site from May – October 2011. There were five rows of 45 centimeter raised planting beds on 1.22 meter centers in each HT and OF plot. The outer two rows served as guard rows, and the inner three rows were test rows. Rows were subdivided into nine 3-meter subplots per plot. The three crops were randomly planted within each of the plots (Figure 1).
Fertilizer application rates were based on six 1.22 by 91.4 meter rows. The test rows were fertilized with an 8-24-24 fertilizer at a rate of 50 Lbs. acre-1, based on the formula:
(Amount N needed per acre/% N in Fertilizer)x 100

(2012 Vegetable Crop Handbook for Southeastern U.S.). The fertilizer was banded in the rows with a 1972 International Harvester Farmall 140T with a fertilizer distributor. The fertilizer distributor was calibrated to deliver approximately 50 pounds acre-1. Netafim™ Drip tape (12 inch spacing for emitters) was installed at a depth of 5 cm. All rows in HT and OF plots were covered with 1.25 millimeter thick, 48 inch wide black plastic mulch to aid in weed suppression, raising soil temperatures, and water management.
The varieties of crops grown were “Saladbowl” leaf lettuce, “Giant of Italy” leaf parsley and “Calypso” cilantro (Johnny’s Selected Seeds). Lettuce was seeded 6 weeks prior to planting, and Cilantro and parsley was seeded four weeks prior to planting, in 98 cell trays with Sungro Sunshine Mix #8 media. The trays were germinated and grown in a greenhouse and moved outside three days prior to planting to harden off the transplants. Lettuce and parsley were planted in double rows within the subplot in two rows per subplot, 30 cm apart (20 plants per subplot). Calypso cilantro was planted in a quincunx pattern, 10 cm apart (29 plants per subplot). The first transplants were planted on January 10, 2011, in their respective subplots, with a new crop transplanted every 30 days for 3 months (First planting: Lettuce – L1; Cilantro – C1; Parsley – P1. Second Planting: Lettuce – L2; Cilantro – C2; Parsley – P2).
Photosynthetically active radiation (PAR), soil and air temperatures, relative humidity, and soil moisture were recorded with Decagon Em50 data loggers on an hourly basis. One data logger was placed in each plot. The logger sensors were placed 5 meters from the data logger on the center row due to cord length. One ECH20 temperature sensor was placed at a depth of 2 cm in the soil and another for measuring air temperature was placed 15 cm above the plastic mulch. A 5TM sensor was placed 5 m in the other direction to record soil moisture and temperature at a depth of 2cm. An EHT sensor was placed 15 cm above the mulch near the 5TM to record relative humidity and air temperature. One PAR sensor was placed in an open field plot and a high tunnel plot approximately 30 cm above the row top. The PAR sensors were placed on a base 15 cm above the row top on the side of the center row in the center of the HT or OF plot.
After initial planting, plant height, width, and chlorophyll measurements were taken every two weeks. Chlorophyll measurements were taken with a Minolta 502 Plus chlorophyll meter. The measurements were taken from eight randomly selected plants. Height of the plants was taken at the apparent apex of the largest mass of growth and width was taken at the apparent mean width of growth. Soil/plant analysis development (SPAD) readings were taken on five to seven randomly chosen leaves around the plant, and averaged using the average function on the SPAD meter. Plants were harvested at the first sign of bolting or according to the schedule after planting date: lettuce, 30 days; cilantro, 55 days; parsley, 60 days. Upon harvest, harvest and market weights were taken. Harvest weight was the plant cut at the base and weighed while market weight was the trimmed product for sale. After weighing in the field, samples were placed in plastic bags and stored in an ice chest (with ice) for transport for lab analysis. Three of the eight plants harvested were sampled for nitrates and leaf area. Nitrates were analyzed with a Hardy Twin nitrate meter. The lower three inches of 8 to 10 stems were removed, and then minced on a plastic cutting board. Lettuce and parsley stems samples were extracted and tested whereas cilantro samples required the addition of 5ml of distilled water for extraction. Leaf area was measured from the most recently matured leaves (including stems) using an optical leaf area meter (LI-3100C, Li-COR Biosciences, Lincoln, NE). Stems were not removed from the cilantro or parsley as it is commonly sold with these crops. Test equipment was calibrated prior to each use as per manufacturer’s instructions.

The remaining samples were placed in a forced air drier at 50?C for two weeks. Samples were weighed for dry weight and then sent to the L.S.U. Soil Test and Plant Analysis Lab for the Ag Routine Metals Package plus total carbon and nitrogen.
All harvest and market weights, dry weights, and tissue analysis results were analyzed for significance using SAS/STAT® software’s Proc Mixed and means separated using Saxton’s macro. The data was analyzed by treatment effect, planting date effect, and treatment by planting date interaction.
Temperatures recorded by the data logger were used to compute GDD for the main treatments. Mean, minimum, and maximum soil and air temperatures, soil moisture, relative humidity, and PAR were determined using SAS/STAT® software’s Proc Means. GDD were calculated with the following formula: (( Tempmax + Tempmin ) / 2 ) – TempBase. The base temperature was established at 15.55°C and GDD was calculated for each crop for each planting period. Total GDD was then summed for each crop for each planting period. The daily and overall means of environmental parameters (Soil moisture and temperature, PAR, relative humidity) for the crop growing periods were also determined from the SAS/STAT® software’s Proc Means output.
Budgets were generated using an excel spreadsheet. A pro forma business form was used and reflects the costs of inputs and potential profits generated. The Pro forma budgets include input costs but do not take into account depreciation on the high tunnels, or potential tax deductions on crop supplies. The selling price was set at $1.00 for 4 oz. bunch for lettuce, cilantro, and parsley. This price/unit was determined to be at the high end charged in the local area and would offer conservative profitability estimates. The potential profit generated by each crop was calculated with the formula:
(((Mean Market Weight x 0.035274a) x bK/ 4 oz.c) $1.00d)

a0.035274 to convert grams to ounces
bK = 500 lettuce and parsley plants / 1000 ft2
bK = 750 cilantro plants / 1000 ft2
cTotal ounces / four ounces to determine quantity of 4 oz bunches
d$1.00 is cost per 4 oz. bunch

There were 60 parsley and lettuce plants and 87 cilantro plants per plot. Because the setup of the two treatments was practically identical, the financials provide another method of comparing the different yields and variations through the profits generated.
All plants were harvested at one time per planting to simulate a single-harvest for market. Expected revenues were compared between treatments within plantings, and then compared between planting dates.

Research results and discussion:

Results and Discussion/Milestones
One of the first benefits of HT use was realized three days after the January 10 planting. High winds moved through the research area and stunted the OF plants, whereas the HT plants sustained little to no effects. There was no data collected to quantify this, but the OF plants were retarded by about two weeks. Irrigation issues shortly after transplanting resulted in the loss of the third planting.
Overall, HT crops showed a greater marketable yield over the OF crops. Only parsley showed any significant difference (Table 1a). The L1 HT harvest and market yields were lower than the OF harvest and market yields. The widths of HT and OF L1 had no differences, but HT L1’s height almost 5 cm taller than OF L1.was larger Second planting crops were significantly greater than first planting. By treatments within the second planting, HT C2 and P2 produced larger harvest and market yields then OF C2 and P2 (Table 1b).
Environmental parameters (soil temperature and moisture, air temperature, relative humidity and PAR) were not compared for significance. There are relatively minor contrasts between treatments within the same planting, but there is greater contrast between plantings (Table 2). PAR showed greater divergence between treatments as well as planting dates (Table 2).
Bi-weekly height, width and SPAD revealed significant differences only in L1, P1, and P2 heights (P<.05), and no differences in widths or SPAD (Table 3).
Overall differences in nitrate levels were seen in cilantro and parsley (Table 4a). Nitrate differences were also shown between planting dates. HT P1 and P2 had overall higher nitrate levels than OF P1 and P2. P1 and P2 had significantly higher nitrates by planting date (Table 4b).
Tissue analysis produced only a few significant differences between HT and OF crops overall. HT lettuce had tested higher in Ca and K, HT cilantro in Na, and OF parsley in C and HT parsley in Fe (Table 5a). By planting date, lettuce had higher Ca, K, S, and Zn in planting 2, and higher C in planting 1 (Table 5b). Cilantro exhibited higher Cu, P, S, and Zn in planting 2. Parsley showed differences in C between HT and OF by planting dates, but no differences within treatments (Table 5b).
GDD was higher in the HT and in the second planting (Table 4b). Leaf area was higher in the HT with the exception of lettuce (Table 4a). Leaf area by planting date was only higher in HT parsley, P1 being greater than P2 (Table 4b).

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:


Project Outcomes

Project outcomes:

High tunnels have the potential to increase marketable yield in cilantro and parsley. HT lettuce may not be as profitable and growing it in an open field may prove to be a better option in the long term. One season is not enough time to determine the effectiveness of high tunnels for lettuce, cilantro and parsley, but further investigation will provide stronger evidence one way or the other. The 2012 growing season was fairly mild, with temperatures near freezing for only a few nights. Many years, the Gulf south experiences cooler temperatures and high tunnels may prove to be more beneficial. Another approach is to consider a single row planted with a culinary herb that is in demand in the local market. The initial cost of high tunnel may not be meet by a single crop in a single growing season. With the financial incentives offered through NRCS EQIP grants, the profit margin for HT grown crops increases. Even with the amount of cost absorbed by the farmer, depreciation would offset the initial expense of HT use.

Economic Analysis

Gross revenues for the first planting lean towards open field production for lettuce and cilantro. First planting HT parsley gross revenues potentially yielded $1,059.59, whereas OF P1 yielded only $328.58. OF lettuce and cilantro gross revenues were $71.22 and $34.23 greater than HT first planting lettuce and cilantro. Second planting HT crop offered greater potential profits. HT second planting lettuce, cilantro and parsley gross revenues exceeded OF second planting crops by $37.57, $280.36, and $360.87 respectively. When OF treatments had higher potential revenues, the differences were much smaller than the instances when HT treatments had potentially greater yields. The risks of purchasing high tunnels are greatly reduced while grants are available. Longer studies would better solidify the effectiveness of HT herb production.

Farmer Adoption



Areas needing additional study

Depending upon local market demands for herbs, high tunnel herb production, as a whole needs to be looked into further. Culinary herbs such as chervil have great potential if there is a market for them. Many herbs are very costly, if available at all in many local markets. Summer production of herbs and lettuces in high tunnels, with shade cloth is another area, which need to be investigated. Summers are too hot for conventional production methods and high tunnels could provide a cooler growing environment. Most growers would probably utilize high tunnels for tomatoes, or other high profit items. Salad greens remain a highly sought after product and summer production could open up an additional cash crop for small to medium farmers. Another area that needs to be pursued is herbs and salad greens as a winter HT cover/cash crop. They could be planted with no inputs to utilize residual fertilizer and nutrients from the previous season’s crop.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.