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

Abstract

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 blossomend 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. INTRODUCTION Work by Van Ieperen (1996) recorded a 22 % increase of production and significant reduction of blossom-end rot in tomatoes due to a low daytime electrical conductivity (EC) compared to a control. A daytime EC of 1.0 was combined with a nighttime EC of 9 mS/cm and the control had a constant EC of 5 mS/cm. These results were found during spring and early summer but not in autumn. The increase in production was the rationale for the present experiments. The objective was to determine whether the same results could be achieved under semi-practical conditions, since the work of Van Ieperen was done on a short period only with low production levels compared to practical situation. In addition the aim was to study the effects on fruit quality, which was not observed by Van Ieperen. Two experiments with tomato were conducted. The first experiment confirmed the positive effect on production as found by Van Ieperen, but there was a negative effect on fruit quality. In the second experiment, it was tested whether the principle could be used to achieve non adverse effect on the quality, by lowering the EC during the day at high radiation only. Proc. IS on Soilless Cult. and Hydroponics Ed: M. Urrestarazu Gavilan Acta Hort. 697 ISHS 2005