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

View the project final report

Commodities

• Additional Plants: herbs

Practices

• Crop Production: application rate management, crop rotation, irrigation, tissue analysis
• Farm Business Management: budgets/cost and returns
• Production Systems: general crop production
• Sustainable Communities: sustainability measures

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.

Introduction

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.

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.