A microcomputer‐controlled system for the automatic measurement and maintenance of ion activities in nutrient solutions during their absorption by intact plants in hydroponic facilities

A microcomputer‐based system for the measurement and maintenance of ion concentrations in hydroponic facilities is described. It is based upon the use of ion‐specific electrodes, is entirely automatic, and enables the experimenter to maintain ion concentrations as low as 25 mmol m−3 NO3− and K+ in hydroponic facilities of relatively low volume (26 dm3). The system enables the operator to store values for ambient temperature, irradiance, and any ion concentrations (including pH) which can be measured by means of ion‐specific electrodes. The components of this system are all available commercially so that the whole unit can readily be assembled. The advantages of the computer control extend to the manipulation and display of collected data.