Production of Tomato Fruits with High Brix in Nutrient Solution Cultivation System with Granular Rockwool. (Part 2). Analysis of Influence of Water Content, pF and Kind of Granular Rockwool on Transpiration of Tomato Plants.

The authors have been making a series of researches for the production of tomato fruits with high Brix in the nutrient solution cultivation system with granular rockwool. For the production of tomato fruits with high Brix, the rockwool has to be kept low water condition. In order to control the irrigation under low water condition, the transpiration rate of tomato plants under low water condition has to be analyzed. The experiment was carried out in a glasshouse in Ehime University in 1999. As the results of the measurement of the pF of three kinds of granular rockwools (granularrockwool (1), granular rockwool (2) and their mixture), it was made clear that the pF increased rapidly at a certain value of water content in the process of the decrease of water content and that the value was particular to each granular rockwool. In the measurement of the transpiration rate of tomato plants (Lycopersicon esculentum Mill. cv. Hausu-Momotaro), three treatments were tested. The granular rockwool in the treatment 1 had the saturated water content (1740 g·pot-1), and the water content in the treatment 2 and the treatment 3 were 750 g and 1500 g less than the water content in the treatment 1 respectively. The wight of the rockwool cube and the granular rockwool were 107 g and 120 g respectively. The transpiration rate and water potential of leaf in the treatment 2 were about the same as those in the treatment 1. On the other hand, much lower transpiration rate and water potential were observed in the treatment 3. The diurnal changes in the transpiration rate in the three kinds of granular rockwools showed that the transpiration rate was affected by the pF which was determined by the water content and the kind of the granular rockwool.