Effects of diurnal EC variations on fruit yield and quality of greenhouse tomatoes grown in rockwool

This study tested a variable EC fertigation strategy, which provided plants with a low EC nutrient solution in late morning & noon and a high EC nutrient solution in the afternoon & night, to improve tomato fruit quality without compromising yield in a spring crop grown in rockwool. Eight treatments were applied: 3 constant EC treatments (2.5, 3.75, and 5.0 mS cm(-1)), 3 variable EC treatments (1.5 to 8.5 mS cm(-1), with 24-h averages of 2.5, 3.75, and 5.0 mS cm(-1)) and 2 variable EC treatments with reduced rockwool slab size (1.5 to 8.5 mS cm(-1), 24-h averages of 3.75, and 5.0 mS cm(-1)). We found that the variable EC fertigation improved tomato growth, fruit yield and quality but the effect varied with the EC level and plant growth stage. A variable EC fertigation with a 24-h average of EC of 2.5 mS cm(-1) was the best in early growth period while a variable EC fertigation with a 24-h average EC of 3.75 mS cm(-1) and good correspondence between slab EC and solar radiation was the best in late growth period. The increase in tolerance to high EC in late growth period might be related to higher photoassimilate production from strong solar radiation.