Comparative Leaf Tissue Analysis of Potassium Deficiency and a Disorder Resembling Potassium Deficiency in Thompson Seedless Grapevines

¹ University of California Kearney Agricultural Center, 9240 S. Riverbend Avenue, Parlier, CA 93648
² Fresno County Farm and Home Advisors Office, 1720 S. Maple Avenue, Fresno, CA 93702.

Studies were conducted in 1979 and 1980 and in 1985 to determine mineral nutrition differences associated with a disorder referred to as "false potassium" (FK). FK affected vines temporarily manifest potassium deficiency-like symptoms on basal leaves in a period preceding bloom. In both studies symptom and nonsymptom leaf petioles and blades were sampled at the time of symptom development and later when symptom development ceased. For comparison, "true potassium" (TK) deficient vineyards continued to be sampled until veraison in 1985. The FK vines had higher total nitrogen (N) and ammonium nitrogen (NH₄-N) and lower potassium (K) in the leaves at symptom development. The levels then recovered to those of normal leaves by bloom when symptom development ceased. The leaf K levels of FK increased with time as symptom development ceased. TK symptom tissue K levels were much lower than those of the FK tissues and continued to decline. FK appears in the spring when cool and/or cloudy weather follows warm weather. Thus, N metabolism problems are thought to be the cause of FK, considering the sensitivity of N assimilation to low temperature and irradiance.

Key words: potassium, nitrogen, ammonium

Submitted on April 2, 1989