Saltzman, S., Institute of Soils and Water, Agricultural Research Organisation, Volcani Center, Bet Dagan, Israel
Heuer, B., Institute of Soils and Water, Agricultural Research Organisation, Volcani Center, Bet Dagan, Israel

A modified leaf disc buoyancy procedure for the detection of photosynthesis‐inhibiting residues in water is described. The modifications proposed, mainly the presence of sodium hydrogen carbonate in the infiltration solution, increased the sensitivity of the method and reduced the time required. The substituted urea and 1,3,5‐triazine herbicides diuron, linuron, monuron, atrazine, ametryn and atraton were detected below 0.7 mg litre−1 using cucumber (Cucumis sativus L., cv. ‘Dalia’) leaf discs. A concentration as low as 0.09 mg diuron litre−1 could be detected. Although bean (Phaseolus vulgaris L., cv. ‘Bulgarian’) leaf tissue was less sensitive in this bioassay than cucumber, 0.3 mg diuron litre−1 could still be detected. The test, being very rapid (less than 30 min per determination) and relatively sensitive, could be used for the detection of photosynthesis inhibitors in recycled water used for irrigation. Copyright © 1985 John Wiley & Sons, Ltd