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°N, long. 71°W), a greenhouse tomato ( Lycopersicon esculentum 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 ≤ 0.01) the proportion of Class 2 fruit by reducing fruit size.