High electrical conductivity and radiation-based water management improve fruit quality of greenhouse tomatoes grown in rockwool

In order to improve fruit quality under the Northern climatic growing conditions prevailing in Quebec, Canada (lat. 47 degrees N, long. 71 degrees W), a greenhouse tomato (Lycopersicon esculentumt Mill. cv. Blitz) spring production experiment was conducted using several irrigation regime and electrical conductivity (EC) levels. The irrigation regime treatments were a function of the global solar radiation, with three thresholds applied to each EC treatment. The irrigation thresholds (KJ.m(-2)) were 1) 468, 2) 540, and 3) 612. Two EC treatments were used: 1) control EC (2.0 to 3.5 mS.cm(-1)) and 2) 30% higher EC than the control (2.6 to 4.6 mS.cm(-1)), which was raised by adding NaCl to 12 mmol.L-1. Plant water potential in summer and in the fall and plant growth after 6 months were not affected by irrigation or EC treatments. Raising the EC increased the Na content of reproductive and vegetative parts and decreased the N concentration of the vegetative parts. The highest EC improved fruit quality by reducing the incidence of fruit cracking. Although marketable yields were not affected by EC (P = 0.09) or irrigation regime (P = 0.08) treatments, higher EC during March to September increased (P less than or equal to 0.01) the proportion of Class 2 fruit by reducing fruit size.