A comparison of methods for measuring phytotoxicity from foliar sprays of ammonium nitrate

Abstract

In a series of experiments, plants of Salvia splendens ’St. John's Fire’ were sprayed to run‐off with NH₄NO₃ solutions that varied from 0.10–1.87 M (0.8–15.0% NH₄NO₃). Damage to young fully expanded leaves was determined by measuring percent visually estimated necrosis, leakage of UV (264 nm) absorbing constituents, K, Ca and phosphate, and post‐treatment dry weight:fresh weight ratio. The average correlation coefficient of percent visually estimated necrosis was 0.992 with leakage of UV absorbing constituents, 0.956 with leakage of phosphate, 0.951 with dry weightfresh weight ratio, 0.919 with leakage of Ca and 0.741 with leakage of K. Leakage of UV absorbing constituents consistently provided the best correlation with the visual degree of leaf burn.