Effect of electrical conductivity and transpiration on production of greenhouse tomato (Lycopersicon esculentum L.)

We investigated the hypothesis that manipulating water out-flow of a plant through the shoot environment (potential transpiration, ET0) in a glasshouse could modulate the effect of salinity/osmotic potential in the root environment upon yield of tomatoes. Contrasting root-zone salinity treatments were combined with two climate treatments - a reference (high transpiration, HET0) and a "depressed" transpiration (low transpiration, LET0). The salinity treatments, characterised by their electrical conductivity (EC) were 6.5, 8 and 9.5 dS m(-1), were always coupled with a reference treatment of EC=2 dS m(-1). In another experiment, concentrated nutrients (Nutrients) and nutrients with sodium chloride (NaCl) at the same EC of 9.5 dS m(-1) were compared. Marketable fresh-yield production efficiency decreased by 5.1% for each dS m(-1) in excess of 2 dS m(-1). The number of harvested fruits was not affected; yield loss resulted from reduced fruit weight (3.8% per dS m(-1)) and an increased fraction of unmarketable harvest. At the LET0 treatments, yield loss was only 3.4% per dS m(-1) in accordance with the reduction in fruit weight. Low transpiration did increase fruit fresh yield by 8% in both NaCl and Nutrients treatments at an EC=9 dS m(-1). Neither EC nor ET0 affected individual fruit dry weight. Accordingly, fruit dry matter content was significantly higher at high EC than in the reference (4% per each EC unit in excess of 2 dS m(-1)) and responded to ET0 to a minor extent. Control of the shoot environment in a greenhouse to manipulate the fresh weight of the product may mitigate the effects of poor quality irrigation water without affecting product quality. (C) 2001 Elsevier Science B.V. All rights reserved.