Effects of Leaching Rate and Renewal of Nutrient Solution on Cucumber Growth in Recirculating Hydroponics Using Organic Medium.

Abstract

Cucumbers were grown in bag cultures with bark and peat medium to establish an appropriate administrative method of nutrient solution. Different volumes of nutrient solutions with a 2.4 dS⋅m-1electric conductivity (EC) were supplied to control the leaching fraction (LF) at 0, 15 and 30% of the applied solutions. The renewal frequencies in reservoir were set at zero or twice. The yield, leaf area, chlorophyll and N content of the leaves were greater in the 15 and 30% LFs than those in the 0%, with no difference between the 15% and 30% LFs. Solution renewal did not affect these parameters, EC and nutrient composition in the reservoir. The poor growth in the 0% LF could be ascribed to osmotic stress because the EC of the nutrient solution in the medium significantly increased. However, there were few differences in the nutrient accumulation inside the medium in all treatments. More than 20 to 40% of the nutrients, except for NH4-N, applied to the plants was discarded by the renewal. These results suggest that if EC 2.4 dS⋅m-1 was adopted for this growing system, more than a 15% LF should flow out to avoid an increased EC in the medium. The renewal of the nutrient solution in reservoirs is not beneficial for the increasing yield.