Specialty crop production in high tunnel systems has greatly expanded in the central United States. Strawberry (Fragaria ×ananassa) may be a viable high-value crop for high tunnel growers, but fall-planted production systems have a high opportunity cost in regard to winter production space. This study investigates the feasibility of spring-planted day-neutral strawberry cultivars in a high tunnel production system in Kansas. Furthermore, the goals of this report are to identify day-neutral cultivars that are successful in this production system and investigate the utility of evaporative cooling (EC), as they relate to fruit yield and marketability as well as incidence of gray mold (caused by Botrytis cinerea). High tunnel trials were conducted at the Kansas State University Olathe Horticulture Research and Extension Center during 2014 and 2015. Six commercially available cultivars were evaluated: Albion, Evie 2, Monterey, Portola, San Andreas, and Seascape in both years. Mature fruit (90% to 100% red) were harvested twice weekly for total and marketable (fruit with no defects) fruit yield. The results indicate that ‘Portola’ had the highest total fruit weight in both years at 0.60 and 0.51 kg/plant, respectively, and was significantly higher than ‘Monterey’, ‘Albion’, and ‘San Andreas’ in both years (P < 0.05). In 2014, ‘Portola’, ‘San Andreas’, and ‘Albion’ produced the largest total fruit average weight (grams/fruit) and were significantly larger than ‘Seascape’ and ‘Evie 2’ (P < 0.05). In 2015, ‘Portola’ had significantly larger fruit than all the other cultivars except San Andreas (P < 0.05). Marketability percent by weight ranged from 76.5% to 88.6% across both years and the highest marketability was observed with ‘Albion’ (89% and 83%) and ‘Monterey’ (85% and 84%) in 2014 and 2015, respectively. An examination of fruit production during the early, mid-, and late seasons was used to determine seasonal dynamics of each cultivar and the high tunnel system. The overall trend was that total fruit weight was highest during the midseason and total average fruit weight was largest in the early season. However, ‘San Andreas’ and ‘Seascape’ had similar levels of production between the early and midseason and had the lowest level of production in the midseason, particularly in the 2015 trial. In our trials, the use of EC did not affect fruit weight or gray mold incidence on strawberry fruit. Based on the crop productivity observed in our study, this production system has the potential to extend the season for strawberry growers in the central United States or provide a high-value rotational crop for existing high tunnel growers that does not require winter production space.

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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.

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.

(1) Background: We assessed the impact of high tunnel coverings and harvest maturity (breaker and light red) on antioxidant capacity, ascorbic acid (AsA), lycopene, β–carotene, and phenolic compound (flavonoid and phenolic acid) accumulation in tomatoes (Solanum lycopersicum) at harvest and postharvest. (2) Methods: The two-year study in Olathe, KS, included six different coverings: a standard polyethylene (standard poly), diffuse poly (diffuse), clear poly (clear), UV-A/UV-B blocking poly (block), 55% shade cloth + standard poly (shade), and removal of standard poly two weeks prior to harvest (movable). (3) Results: Antioxidant capacity increased in fruit grown under the clear covering, compared to the shade covering (p < 0.05); similarly, AsA accumulation increased under the standard and clear coverings, relative to the movable and shade coverings (p < 0.001). Postharvest, at the point of consumption (POC), rutin increased in fruit harvested at light red stage versus breaker stage (p < 0.001), and chlorogenic acid increased in light red harvested fruit by 60% under movable, 55% under shade, and 43% under block covering than breaker harvested fruit (p < 0.01). (4) Conclusions: Based on these results, we conclude that both high tunnel covering and postharvest maturation alter antioxidant capacity, AsA, lycopene, and phenolic compound accumulation profiles by the POC.