High Tunnel Coverings Alter Crop Productivity and Microclimate of Tomato and Lettuce

The implementation of high tunnels has shown to increase marketability and/or yield of tomato (Solanum lycopersicum) and lettuce (Lactuca sativa) crops compared with open-field systems. These structures provide the opportunity to alter light intensity and spectral quality by using specific polyethylene (poly) films and/or shadecloth, which may affect microclimate and subsequent crop productivity. However, little is known about how specific high tunnel coverings affect these parameters. The overall goal of this study was to evaluate the impact of various high tunnel coverings on the microclimate and crop productivity of tomato and lettuce. The coverings included standard, ultraviolet (UV)-stabilized poly film (standard); diffuse poly (diffuse); full-spectrum clear poly (clear); UV-A/B blocking poly (block); standard + 55% shadecloth (shade); and removal of standard poly 2 weeks before initial harvest to simulate a movable tunnel (movable). Microclimate parameters that were observed included canopy and soil temperatures, canopy growing degree-days (GDD), and photosynthetic active radiation (PAR), and crop productivity included yield and net photosynthetic rate. Hybrid red ‘BHN 589’ tomatoes were grown during the summer, and red ‘New Red Fire’ and green ‘Two Star’ leaf lettuce were grown in both spring and fall in 2017 and 2018. Increased temperature, GDD, and PAR were observed during the spring and summer compared with the fall. The soil temperatures during the summer increased more under the clear covering compared with the others. For tomato, the shade produced lower total fruit yield and net photosynthetic rate (Pn) compared with the other treatments, which were similar (P < 0.001 and <0.001, respectively). The greatest yield was 7.39 kg/plant, which was produced under the clear covering. For red leaf lettuce grown in the spring, the plants under the clear, standard, and diffuse coverings had significantly greater yield than the movable and shade coverings (P < 0.001). The coverings had less effect on the yield during the fall lettuce trials, which may have been attributed to the decrease in PAR and environmental temperatures. The findings of this study suggest that high tunnel coverings affect both microclimate and yield of lettuce and tomato.

Exploring Overwintered Cover Crops as a Soil Management Tool in Upper-midwest High Tunnels

High tunnels are an important season extension tool for horticultural production in cold climates, however maintaining soil health in these intensively managed spaces is challenging. Cover crops are an attractive management tool to address issues such as decreased organic matter, degraded soil structure, increased salinity, and high nitrogen needs. We explored the effect of winter cover crops on soil nutrients, soil health and bell pepper (Capsicum annuum) crop yield in high tunnels for 2 years in three locations across Minnesota. Cover crop treatments included red clover (Trifolium pratense) monoculture, Austrian winter pea/winter rye biculture (Pisum sativum/Secale cereale), hairy vetch/winter rye/tillage radish (Vicia villosa/S. cereale/Raphanus sativus) polyculture, and a bare-ground, weeded control. Cover crop treatments were seeded in two planting date treatments: early planted treatments were seeded into a standing bell pepper crop in late Aug/early September and late planted treatments were seeded after bell peppers were removed in mid-September At termination time in early May, all cover crops had successfully overwintered and produced biomass in three Minnesota locations except for Austrian winter pea at the coldest location, zone 3b. Data collected include cover crop and weed biomass, biomass carbon and nitrogen, extractable soil nitrogen, potentially mineralizable nitrogen, microbial biomass carbon, permanganate oxidizable carbon, soil pH, soluble salts (EC), and pepper yield. Despite poor legume performance, increases in extractable soil nitrogen and potentially mineralizable nitrogen in the weeks following cover crop residue incorporation were observed. Biomass nitrogen contributions averaged 100 kg·ha−1 N with an observed high of 365 kg·ha−1 N. Cover crops also reduced extractable soil N in a spring sampling relative to the bare ground control, suggesting provision of nitrogen retention ecosystem services.

The diversity of Passalora fulva Isolates Collected from Tomato Plants in US high tunnels

High tunnels extend the growing season of high value crops, including tomatoes, but the environmental conditions within high tunnels favor the spread of the tomato leaf mold pathogen, Passalora fulva (syn. Cladosporium fulvum). Tomato leaf mold results in defoliation, and if severe, losses in yield. Despite substantial research, little is known regarding the genetic structure and diversity of populations of P. fulva associated with high tunnel tomato production in the United States. From 2016 to 2019, a total of 50 P. fulva isolates were collected from tomato leaf samples in high tunnels in the Northeast and Minnesota. Other Cladosporium species were also isolated from the leaf surfaces. Koch’s postulates were conducted to confirm that P. fulva was the cause of the disease symptoms observed. Race determination experiments revealed that the isolates belonged to either race 0 (six isolates) or race 2 (44 isolates). Polymorphisms were identified within four previously characterized effector genes Avr2, Avr4, Avr4e, and Avr9. The largest number of polymorphisms were observed for Avr2. Both mating type genes, MAT1-1-1 and MAT1-2-1, were present in the isolate collection. For further insights into the pathogen diversity, the 50 isolates were genotyped at 7,514 single-nucleotide polymorphism loci using genotyping-by-sequencing: differentiation by region but not by year was observed. Within the collection of 50 isolates, there were 18 distinct genotypes. Information regarding P. fulva population diversity will enable better management recommendations for growers, as high tunnel production of tomatoes expands.

Spectral Blocking of Solar Radiation in High Tunnels by Poly Covers: Its Impact on Nutritional Quality Regarding Essential Nutrients and Health-Promoting Phytochemicals in Lettuce and Tomato

Spectral characteristics of solar radiation have a major role in plant growth and development and the overall metabolism, including secondary metabolism, which is important for the accumulation of health-promoting phytochemicals in plants. The primary focus of this study was to determine the effect of spectral characteristics of solar radiation on the nutritional quality of lettuce (Lactuca sativa L., cv. red leaf ‘New Red Fire’ and green leaf ‘Two Star’ and tomato (Solanum lycopersicum L., cv. BHN-589) grown in high tunnels in relation to the accumulation of essential nutrients and phytochemicals. Solar spectrum received by crops was modified using photo-selective poly covers. Treatments included commonly used standard poly, luminescence poly (diffuse poly), clear poly, UV blocking poly, exposure of crops grown under the standard poly to full sun 2 weeks prior to harvest (akin to movable tunnel), and 55% shade cloth on the standard poly. All the poly covers and shade cloth reduced the PAR levels in the high tunnels, and the largest reduction was by the shade cloth, which reduced the solar PAR by approximately 48%. Clear poly allowed the maximum UV-A and UV-B radiation, while standard poly allowed only a small fraction of the solar UV-A and UV-B (between 15.8% and 16.2%). Clear poly, which allowed a higher percentage of solar UV-A (60.5%) and UV-B (65%) than other poly covers, increased the total phenolic concentration and the antioxidant capacity in red leaf lettuce. It also increased the accumulation of flavonoids, including quercetin-3-glucoside, luteolin-7-glucoside, and apigenin-3-glucoside in red leaf lettuce, compared to the standard poly. Brief exposure of crops grown in high tunnels to full sun prior to harvest produced the largest increase in the accumulation of quercetin-3-glucoside, and it also resulted in an increase in luteolin-7-glucoside and apigenin-3-glucoside in red leaf lettuce. Thus, clear poly and brief exposure of red leaf lettuce to the full sun, which can increase UV exposure to the plants, produced a positive impact on its nutritional quality. In contrast, shade cloth which allowed the lowest levels of solar PAR, UV-A and UV-B relative to the other poly covers had a negative impact on the accumulation of the phenolic compounds in red leaf lettuce. However, in green leaf lettuce, luminesce poly, clear poly, UV-block poly, and shade treatments increased the accumulation of many essential nutrients, including protein, magnesium, and sulfur in green leaf lettuce compared to the standard poly. Poly cover treatments including shade treatment did not affect the accumulation of either carotenoids (lutein, β-carotene, and lycopene) or essential nutrients in mature tomato fruits. The results show that clear poly cover can enhance the accumulation of many phenolic compounds in red leaf lettuce, as does the brief exposure of the crop to the full sun prior to harvest. Thus, UV radiation plays an important role in the accumulation of phenolic compounds in red leaf lettuce while the overall spectral quality of solar radiation has a significant influence on the accumulation of essential nutrients in green leaf lettuce.

Winter Production of Asian Leafy Greens in High Tunnels Using Biodegradable Mulches

Use of season extension tools such as high tunnels and diverse vegetable crops have been crucial in improving competitiveness of vegetable growers in Mississippi who operate on small- to medium-sized farms. Chinese cabbage, also known as pak choy or bok choy, has become increasingly popular due to numerous cultivar choices, fast maturity, high productivity, tolerance for frost, and its potential use for winter production in high tunnels in a subtropical climate. Five Chinese cabbage cultivars including ‘Asian Delight’, ‘Black Summer’, ‘Red Pac’, ‘Rosie’, and ‘Tokyo Bekana’ were evaluated for plant growth, yield, and mineral nutrient concentrations when grown with three types of biodegradable plastic mulches (BDMs) and one polyethylene (PE, or plastic) mulch in a high tunnel in two experiments from 30 October 2019 to 18 March 2020. The five tested cultivars varied in plant height, widths, leaf SPAD, fresh and dry plant weights, marketable yield, and macro- and micro-nutrient concentrations. ‘Tokyo Bekana’ produced the highest marketable yield and fresh and dry plant weights in both experiments. The three BDMs resulted in similar marketable yield and mineral nutrients in tested cultivars and similar temperatures of leaf, mulch, and substrate compared to the PE mulch. The high tunnel provides a viable way for the winter production of selected Chinese cabbage cultivars in a subtropical climate with possible different yields between production cycles due to varying microenvironment in those months.

Effect of Light Characteristics on the Sensory Properties of Red Lettuce (Lactuca sativa)

Leafy green production in high tunnels (HTs) results in increased yields, improved visual quality, and extended production with polyethylene (poly) film and/or shade cloth coverings. However, altering visible and ultra-violet light with HT coverings may reduce phytochemicals, thus influencing plant pigmentation and taste. The objective of this study was to examine various HT coverings on the sensory perceptions, soil temperature, color, and anthocyanin accumulation of red leaf lettuce. The coverings included standard poly, standard poly with removal two weeks prior to harvest (movable), diffuse poly, clear poly, UV-A/B blocking poly (block), standard poly with 55% shade cloth, and the open field. A highly trained descriptive panel evaluated the samples using a scale from 0 (none) to 15 (extremely high) and determined a list of 20 sensory attributes. The color intensity attribute had the most differentiation between coverings, and the open field was higher (i.e., darker) than the others at 7.5 (p < 0.0001), followed by clear and movable coverings at 6.8, and the shade covering scored a 2. Strong relationships existed between both colorimetric (hue°) and anthocyanin analysis to panelist-based scores (R2 = 0.847 and 0.640, respectively). The initial crispness was similar for movable, standard, diffuse, and block coverings at 5.3 on average, which was higher than the open field at 4 (p < 0.01). The open field lettuce grew under cooler soil temperatures, which may have slowed down maturation and resulted in softer tissue. Based on this study, HT growers can implement specific coverings to cater to markets that value visual quality.

Farm Type and High Tunnel Management: Connections between Farm Characteristics and High Tunnel Outcomes in Indiana

High tunnels are a low-cost technology that can strengthen local and regional food systems and have been shown to help farmers extend the growing season and increase the yield and shelf life, and improve the quality of their crops. This study addresses a need for a better understanding of farmers’ experience with integrating high tunnels into their operations, to understand the human dimensions of high tunnel management. We present an analysis of survey and interview data to examine how farm characteristics affect the outcomes of growing specialty crops in high tunnels. Our findings show that farmers managing different types of farms have taken distinct approaches to integrating and managing high tunnels on their farms, with important implications for farm-level outcomes. We identify three types of farms commonly adopting high tunnels in Indiana: 1) alternative food and agriculture enterprises (AFAEs) are consumer-oriented, small-scale farms that sell their products directly to their customers in relationship-based market networks such as farmers’ markets and community-supported agriculture; 2) mixed enterprise farmers have larger operations and sell into both conventional commodity markets and direct markets; and 3) side enterprise farmers operate small-scale enterprises and their primary household income comes from off-farm employment or another business. Farm type is associated with divergent levels of time and labor investment, resulting in higher capacity use of high tunnels and greater financial return for AFAE farmers who make high tunnels central to their business, compared with mixed and side enterprise farmers who invest less time and labor into their high tunnels. We explain how farm characteristics and approaches to adopting the infrastructure shape farmers’ success and high-capacity use of high tunnels.

Improving Snapdragon Cut Flower Production through High Tunnel Season Extension, Transplant Timing, and Cultivar Selection

The demand for locally grown, specialty cut flowers is increasing and now includes nontraditional regions for production, such as the U.S. Intermountain West. The objective of this study was to evaluate snapdragon (Antirrhinum majus L.) as a cool season, cut flower crop in northern Utah, where the high elevation and semiarid climate result in a short growing season with strong daily temperature fluctuations. High tunnel and field production methods were trialed in North Logan, UT (41.77°N, 111.81°W, 1382 m elevation) with cultivars ‘Chantilly’, ‘Potomac’, and ‘Rocket’ in 2018 and 2019. Each year, five to six transplant timings at 3-week intervals were tested, beginning in early February in high tunnels and ending in late May in an unprotected field. Stems were harvested and graded according to quality and stem length. High tunnels advanced production by 5 to 8 weeks, whereas field harvests continued beyond the high tunnel harvests by 2 to 8 weeks. High tunnels yielded 103 to 110 total stems per m2 (65% to 89% marketability), whereas field yields were 111 to 162 total stems per m2 (34% to 58% marketability). Overall, production was the greatest with March transplant timings in the high tunnels and mid-April transplant timings in the field. ‘Chantilly’ consistently bloomed the earliest on 4 and 6 May each year, ‘Potomac’ had the highest percentage of long stem lengths, and ‘Rocket’ extended marketable stem production through July in high tunnels. Selecting optimal transplant dates in the high tunnel and field based on cultivar bloom timing maximizes marketable yields and results in a harvest window lasting 4.5 months.

Influence of irrigation regimes on yield, pomological parameters and population development of Tetranychus cinnabarinus Boisd. (Acari: Tetranychidae) in strawberry

In this study, the effect of full (IR100), 50% (IR50), 75% (IR75) and 125% (IR125) irrigation levels on population development of the carmine spider mite (CSM) as well as on yield and some pomological properties of ‘Fortuna’ strawberry cultivar grown in high tunnels were evaluated in two consecutive growing seasons (2016–2017 and 2017–2018). The numbers of CSM were significantly lower on strawberry leaves which were irrigated by IR50 and IR75 in both growing seasons. Full (IR100) and highest (IR125) irrigation levels were the most favorable for the development of CSM populations. On the other hand, in the CSM thriving period (2017), the fruit weight was generally high in the plots with the highest irrigation (IR125) level. Although there was no interaction with the CSM population, fruit acidity (%) increased in the IR100 and IR125 irrigation levels, possibly due to stress in plants, when CSM population was highest (in March). In the absence of CSM, fruit acidity was significantly high in the plots where water stress was experienced. While no significant interaction was found between the pomological characters and the CSM population, the mites affected the yield significantly in that plants were more productive under IR 75 even when there was a CSM population. This study suggests that the application of IR75 level in Fortuna strawberry is related to lower CSM population growth and significantly higher yields.