Tuesday, July 31, 2012
Grand Ballroom
While the majority of U.S. strawberries are produced in open fields, greenhouse soilless culture is considered suitable for local production in urban or suburban settings. The University of Arizona Controlled Environment Agriculture Center has initiated a small research program evaluating strawberry (Fragaria ×ananassa) as a potential alternative crop grown in semiarid greenhouse since 2009. ‘Albion’ and ‘Camino Real’ plantlets were transplanted into two rows of a Styrofoam raised trough system (Ishiguro Nozai, Japan). The troughs were filled with a mix of 50% coco-coir and 50% perlite. Drip irrigation was applied with the modified Yamazaki strawberry solution twice or three times a day to obtain a target drainage rate of ~30%, pH ~6.5 and EC 1.0. Major challenges include: 1) maintaining optimum root zone environment and 2) preventing tip/calyx burn. The former issue required the selection of substrates having appropriate chemical and physical characteristics and the application of a periodic water flush of root zone to reduce excessive salts. Tip/calyx burn was associated with the relatively high VPD in the greenhouse, causing excessive transpiration and lower turgor to limit calcium supply to the growing meristematic tissues. Earlier study showed that guttation is a plant health indicator for strawberry suggesting a turgor sufficient to supply calcium and can be observed under low night time VPD (< 0.1 kPa; Bradfield and Guttridge, 1979). For this reason, we examined a night time application of floating cover on top of strawberry canopy to maintain high humidity (low VPD) inside the cover. A clear polyethylene film was used for the cover and treatment was applied from sunset to shortly after sunrise every day for 40 days (4/16 – 5/26/2010). Guttation was observed for plants under floating cover almost every morning while no guttation was observed for untreated plants. The night time high humidity treatment exhibited significantly lower percent calyx burn (16.7%) and tip burn (9.0%) than non-treated control (48.6% and 47.2%, respectively) throughout the experiment. When uncovered, Cultivar ‘Camino Real’ had more tip/calyx burn (58.9%) than ‘Albion’ (37.0%). The nighttime average VPD was 0.09 kPa under the floating cover and 0.88 kPa in air inside the greenhouse. No particular difference was observed for disease, as foliage was completely dry during the day (average VPD: 1.6 kPa) For a larger scale operation, automated curtain may be a possibility as a low cost solution of tip/calyx burns for strawberry grown in semiarid greenhouses.