PRODUCTION AND QUALITY OF TOMATO AS AFFECTED BY RADIATION-REGULATED ELECTRICAL CONDUCTIVITY OF DRIP SOLUTION

Two experiments with tomato were conducted to see whether a high nighttime EC combined with low daytime EC can give a higher yield without adverse effects on the quality. In the first experiment EC levels for day and night were set. In the second experiment the EC in the drip solution was lowered in proportion to the increase in global radiation. Tomato was grown in a long lasting crop cycle (almost a year round) in pumice using small rooting volumes per plant. Production, shelf life, refraction, and taste were determined. The taste was calculated from the results of instrumental analysis and a model. In the treatments where the EC was lowered compared to a control treatment, fruit production was higher due to higher fruit weight, but there were negative effects on taste, refraction, acidity and gold specks of fruit. Positive effects of lowering the EC were higher Ca contents in the fruit and lower incidence of blossom-end rot compared to constant EC. The effects were caused by the low EC during the day. The EC level chosen for control turned out to be very important. The control EC (during the day) in the drip solution was 3.0 – 3.3, resulting in run-off EC levels of ~4.0 mS/cm. This was too high to achieve maximum production. The recommendation is to reduce the EC of the drip irrigation on sunny days in proportion to the radiation or transpiration. Under Dutch climatic conditions, the EC should not be reduced as low as 1.0 mS/cm.