Methods to assay absorption of foliar applied nutrients and removal of unabsorbed residue 1

Various glues and adhesives were tested for their ability to remove the unabsorbed residue from drops of foliar applied radioactive nutrients to Ficus benjamina L. and Glycine max Merr. Most glues/adhesives adequately removed the unabsorbed residue from nutrients that dried forming a salt deposit on the leaf surface, but only 1.6–3.2% agar, Rhoplex 33, and Elmers Glue removed greater than 95% of the residue from nutrients that formed a moist hygroscopic residue on the leaf surface. Adding 25 mM KH₂PO₄ to 3.2% agar, followed by swabbing the treated area with lN HCl‐1% Liquinox detergent removed all unabsorbed residue from monovalent and divalent cationic an anionic nutrients including heavy metals. Methods to assay foliar absorption were compared by applying “Rb phosphate to leaves of intact plants, excised leaves and leaf discs. Excised leaves with their petiole or stem bases in water behaved similar to intact plants, whereas excised leaves or discs maintained in in a moist atmosphere behaved atypically due to slower and incomplete drying compared to intact plants.