Ammonium toxicity in chrysanthemum: Critical level and symptoms

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Abstract
Three experiments were conducted to determine the critical meq NH4/meq K ratio in fresh tissue indicative of ammonium toxicity and the symptoms of the same under winter and summer conditions. Three and four levels each of ammonical N and K fertilization were employed in factorial designs. The chrysanthemum cultivars Bright Golden Anne and Yellow Mandalay were studied. Results indicate there was a critical range of NH4/K ratios from .025 to .026 below which NH4 injury never occurred and above which injury always occurred. The occurrence of injury within the range was erratic. Confidence limits for the critical range, based on one standard deviation as determined in Experiment 3, extend from .022 to .029. This range was applicable from the second to ninth week of plant growth and for winter crops as well as the summer crop. Symptoms of toxicity include reduction in growth rate, the development of small necrotic spots beginning on middle to lower leaves and progressing up the plant, thickened‐leathery leaves, reduction in root growth, brown roots, and eventual death of the plant.