Growing strawberries with superimposed levels: effect on fruit yield and quality

This experiment was carried out in 2017 and 2018 to assess the effect of increasing plant density by superimposing immovable levels of crop gutters. The greenhouse glazing was an air-inflated double layer of F-CLEAN^®. The inside layer was diffused F-CLEAN^®, in order to reduce the direct shading of the lower levels by the upper levels. In this multi-span greenhouse were arranged, each in an 8 m wide span: a) the traditional single level crop of 7 cropping lines, density 8.75 plants m^‑2; b) three levels of five cropping lines each (18.75 plants m^‑2, vertical spacing between gutters: 1.5 m). In the three-level dispositions, the immovable crop gutters were vertically aligned: all the cropping operations could be done walking or using mobile platforms to adjust the working height to the upper levels. The French early cultivar 'Gariguette' was grown as a soilless heated crop with tray plants planted on December. PAR light at the top of the canopy during the first flush was highly reduced on the lower (-58%) and the intermediate (-40%) levels and, even, slightly decreased on the upper level (-14%), compared to the traditional single-level crop. The changes observed in the levels of total soluble solids content (%Brix) and titratable acidity due to shading were fairly limited and acceptable on the intermediate level. On the lower level, total soluble solids contents remained quite stable during the picking period, while the upper level and the single level crop exhibited a global trend of increasing values between the beginning and the end of the picking period. Yield plant^‑1 was significantly reduced on the lower (-36%) and intermediate (-22%) levels, but not on the upper level. However, with three levels, the higher density m^‑2 led to a higher yield m^‑2, compared to the traditional single-level crop: +76% in 2017, +77% in 2018.