Construction of an Automatic Nutrient Solution Management System for Hydroponics-Adjustment of the K + -Concentration and Volume of Water.

An automatic management system for nutrient solutions was constructed using a programmable logic controller (PLC) and a K ⁺ -ion selective electrode (K ⁺ -ISE). The concentration of K ⁺ was monitored by the K ⁺ -ISE. When the concentration of K ⁺ fell to the threshold limit, an appropriate amount of a concentrated K ⁺ solution was added to the hydroponic solution. The volume was also maintained at a constant level by addition of water. This system can be constructed simply and inexpensively without any computers and pumps.