SCREENING FOR PHYTO-TOXIC CONTAMINANTS IN AN INDUSTRIAL SOURCE OF NUTRIENTS INTENDED FOR FOLIAR AND ROOT FERTILIZATION

Plant screening assays were used to determine whether significant leve ls of growth inhibitory and phytotoxic contaminants were present in a new industrial source of potassium dihydrogen phosphate fertilizer int ended for foliar and root application. Maize (Zea mays L.) plants hydr oponically cultured in a controlled environment chamber, were used for the assays. The threshold concentration of industrial potassium phosp hate which just caused burn damage symptoms, when applied as standard droplets to the leaf surface with Tween 80 wetting agent was 0.5M. The comparative threshold concentration for damage by an ultrapure analyt ical grade of potassium phosphate was >0.6M. Thus, the industrial grad e had slightly higher toxicity for leaf application. Effects on plants of supplying industrial and analytical grade phosphates via the roots were also compared. Root and leaf elongation kinetics, mature leaf ce ll lengths, apparent capacity for leaf cell production, shoot ontogeny , and shoot fresh weight yields were determined at low and high potass ium phosphate concentrations. The effects of analytical and industrial grade fertilizer salts were equivalent. We suggest that these rapid a nd relatively simple plant screening assays can provide a useful safet y check, prior to large scale field trails, for fertilizer nutrients p roduced by new industrial processes.