Evaluation of Organic Romaine Lettuce Yield Under a Protected Environment

The goal of this study is to investigate the performance of multiple romaine lettuce cultivars for spring production under organically-managed high tunnels compared to the open field in Georgia (Zone 8a). The experiment was a split-split-plot design (growing system, planting date, and cultivar) with four replications. Planting dates were 12 March, 2 and 23 April in 2015. Automated sidewall curtains were opened when ambient air temperature exceeded 10°C, and row covers were draped over plants when nighttime temperature was predicted to be ≤0°C. Yields and disease incidence were evaluted over time and hourly microclimate data was recorded for both systems. The following preliminary results reflect the first year of an ongoing two-year study. There was no significant difference among average marketable yield per plot for the high tunnel compared to the field system or among the three different planting dates. However, the romaine cultivar ‘Green Forest’ had a greater marketable yield compared to ‘Red Rosie’ and ‘Freckles’ (p<0.0001). The average head weight, individual plant size (i.e., height and diameter) and number of leaves per head were greater for the 1^st planting date compared to the 2^nd and 3^rd planting dates in both growing systems (p<0.001). The cultivar ‘Super Jericho’ showed the greatest number of leaves compare to ‘Coastal Star’ and ‘Green Forest’ (p<0.05). Non-marketable yields were not significantly different between high tunnels and field systems. However, the cultivar ‘Freckles’ had a greater percentage of non-marketable heads, mainly due to bolting and tip burn incidence (p<0.0001). The most common disorders observed across the study were: bolting, no head formation, lettuce drop (caused by Sclerotinia sclerotiorum) and tip burn. The 1^st planting date had a greater incidence of lettuce drop (19%) compared to the 2^nd (4%) and 3^rd (1%) dates (p<0.01). The 2015 spring season (March-May) was 1.5^oC warmer than the 20^th century average for this region. On the coldest night during the experiment (29 March), the high tunnel air temperature was a minimum of 5^oC warmer than the field system and the high tunnel soil temperature was 4^oC warmer than the field system.