Monitoring Potassium Deficiency in Greenhouse Cucumbers

Posted by Brian Sparks|November 9, 2021

Photo: Texas A&M University

Potassium deficiency of greenhouse cucumbers can be initially observed as chlorosis (yellowing) of the older lower leaf margins. As symptoms progress, interveinal chlorosis and firing (necrosis) of the leaf margin and interveinal regions will develop while the leaf midrib and veins remain green.

A recent e-GRO alert from W. Garrett Owen at the University of Kentucky highlights why managing pH and mineral nutrient concentration in hydroponic solutions is important for maintaining healthy crops and maximizing yield. Routine sampling and analysis of the nutrient solution should be performed to check pH, electrical conductivity, alkalinity, and mineral nutrient concentrations. In addition, leaf tissue sampling and analysis should be performed to determine mineral nutrient concentrations and if any adjustments to the nutrient solution is warranted. When routine sampling and analyses are not performed, nutrient disorders may develop due to pH drift or an imbalance of nutrient uptake relationships.

Nutrient uptake relationships first start with understanding the chemical properties of each mineral nutrient. Though these will not be discussed independently, in general, when fertilizer salts are dissolved in solution, nutrients are essentially available in their ionic form. Each ion is associated with a positive charge (cation) or negative charge (anion), and the number of electrons (valence). Some pairs of nutrients with similar ionic charges are known to have a competitive (antagonistic) or complimentary (synergistic) relationship. This relationship determines how nutrients are taken up the plant and the concentration of the nutrients found in leaf tissue. A perfect example is the potassium (K) – calcium (Ca) – magnesium (Mg) relationship. Potassium has a positive charge (K+) and interacts with other cationic nutrients such as calcium (Ca2+) and magnesium (Mg2+). The interaction among these nutrients is antagonistic which affects their nutrient uptake in the root-zone and concentration of each in plant tissue.

Read the complete e-GRO alert, which includes symptoms of potassium deficiency, corrective steps, and additional resources, here.