2019 ASHS Annual Conference

UV-stabilized polyethylene commonly used for high tunnels reduces spectral quality by blocking UV-B and reducing light intensity by 15-20%. Both light intensity and spectral quality are known to impact the accumulation of several plant nutrients. The objective of this study was to evaluate the effect of 6 different high tunnel coverings (standard polyethylene (standard poly), luminance poly (diffuse), clear poly (clear), UVA+UVB blocking (-UVA/UVB), 55% shade cloth (shade), as well as a simulated movable tunnel (poly removal 2 weeks prior to initial harvest)) on photosynthesis, air and soil temperature, crop yield, storage life, and nutrient content of lettuce (Lactuca sativa L., red-leaf variety ‘New Red Fire’, and green-leaf variety ‘Two Star’). Consecutive fall leaf lettuce trials were conducted at Kansas State University’s Olathe Horticulture Research and Extension Center (OHREC) from October to December, 2017 and 2018. The trials were arranged in a RCBD and four individual high tunnels served as replications. Four-week old seedlings of ‘New Red Fire’ and ‘Two Star’ varieties were transplanted in staggered double rows. Soil/canopy temperatures were measured in 30 min increments. PAR and net photosynthetic rates were measured prior to harvest. For yield, total and marketable head weight (g/head), core length (cm), and leaf area (cm2) was measured. For phytochemical quality, phenolic acid and flavonoid contents (coumarin, chicoric acid, chlorogenic acid, caffeic acid, ferulic acid, rutin, kaempferol, naringenin, quercetin-3-o-glucoside and quercetin) were measured at-harvest and on day 5 after optimum postharvest storage. Storage quality was assessed by water loss (%) and color development throughout storage. Soil temperatures were 2 to 3 °F warmer for the diffuse and clear treatments in comparison to standard, poly removal, and shade treatments (P < .0001). The standard, poly removal, and diffuse treatments of the red and green leaf lettuce had approximately 30% greater fresh weight than the shade treatment (P < 0.05). The poly removal and clear treatments produced darker red pigmentation (P < 0.01) in red leaf lettuce in comparison to the other treatments. High tunnels offer a unique opportunity to manipulate light with various poly films and shade cloths which is not typically applicable for the open-field production. The present study is aimed to identify an optimal balance between production and nutrient content in lettuce, which is critically important for most food crops grown in high tunnels.