Nutrient solution concentration effects on non-drainage irrigation scheduling in coir substrate hydroponic system for tomato cultivation by a FDR sensor

초록

This study examined effects of electrical conductivity (EC) level on irrigation scheduling for tomato (Solanum lycopersicum L. 'Starbuck F1') cultivation aimed at avoiding effluent from coir substrate hydroponic system. The technique utilized a frequency domain reflectometry (FDR) sensor that controlled irrigation to preset volumetric water levels. For comparison, a time-clock scheduling was examined. The volumetric water content in substrate was controlled at 45 or 55% by the FDR, and nutrient solution with pH 5.8 and EC 2.0 or 2.5 mS cm-1 was supplied until about the time of fruit setting on the 4th cluster after transplant. The EC level was then adjusted from 2.0 to 2.0 (EC2.0-2.0), 2.0 to 2.5 (EC2.0-2.5), or 2.5 to 3.0 mS cm-1 (EC2.5-3.0) until the end of the growing season. The EC concentration had a significant effect on daily-averaged irrigation amount and the EC level of substrate. In both of the 45 and 55% water contents, the daily-averaged irrigation volumes were in the order of EC2.0-2.0 > EC2.0-2.5 > EC2.5-3.0 treatment. The EC level of the substrate at the EC2.5-3.0 treatment under the 45% water content was significantly lower than other EC treatments. In addition, significantly lower plant and root growth as well as lower marketable fruit weight were observed at the EC2.5-3.0 under the 45% water content than other EC treatments. In contrast, under the 55% of water content, the higher solution EC did not affect the plant growth and fruit weight. Significantly higher soluble solid content was observed in the fruit grown under the FDR treatments than that under the timer-set system.

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