Decrease of yield of cucumber [Cucumis sativus] by non-renewal of the nutrient hydroponic solution and its reversal by supplementation of activated charcoal

Experiments were conducted to clarify why fruit yield decrease during the late growing-period of cucumber cultured in hydroponic nutrient solution which was not completely renewed but only restored (a non-renewal culture). Furthermore, means to recover the decrease in fruit yield in the non-renewal culture system were investigated. 1) Vegetative growth was unaffected by biweekly total renewal or non-renewal of the culture solution. 2) When the culture solution was supplemented, the yield of "Shogoin-aonaga-fushinari" and !PI 169391" decreased, whereas that of "Hokushin" and "Chojitu-ochiai 2 gou" did not. 3) No decrease in fruit yield was observed when the solution was supplemented with nutrients and activated charcoal. This result suggests that root exudates had induced the decrease in fruit yield, especially by affecting young fruits, because the decrease was reversible through removal of the root exudates by the activated charcoal