Automated composition control of nutrient solution in closed soilless culture systems

A computer algorithm was developed to perform replenishment and reuse of th e drain nutrient solution in close hydroponic systems on the basis of dispe nsing as many nutrients and water in it as were needed to maintain a target electrical conductivity in the irrigation solution. To achieve this in eac h watering application, dilution ratios of the concentrated fertilizer solu tions are automatically adjusted through a computer program based on this a lgorithm, in relation to the volume and the electrical conductivity of the drain solution. It was proved that the returning nutrient solution could be corrected and reused efficiently through this method. However, the concent ration of P, Mn and Zn in the irrigation nutrient solution was extremely lo w in samples taken after continual reuse of the drain solution for a fortni ght. Since the analysed irrigation solution was prepared using a large quan tity of drain solution, it seems likely that reduced P, Zn and Mn concentra tions in the former were due to the high pH of the latter, and this may hav e caused immobilization of these elements. (C) 1999 Silsoe Research Institu te.