K is for Cucumbers

Cucumber plants, like all plants, require all the essential elements to complete its life cycle. However, cucumber plants are particularly “hungry” for potassium (K), they need more potassium than nitrogen to result in high yields.

by Rosa Raudales & Richard McAvoy - greenhouse@uconn.edu

In this e-GroEdible Alert, we cover the role of K in plant growth, the characteristics of K deficiency symptoms, and how to develop a hydroponic nutrient program for production of cucumbers.

The role and mobility of potassium in plants
Potassium plays a key role in plants including activation of enzymes, water balance regulation, energy and protein synthesis, K is involved in photosynthesis and osmotic pressure regulation.

Potassium is a highly mobile element. As described by Horst Marschner (2005) “It is characterized by high mobility at all levels- within the individual cells, within tissues, and in long-distance transport via xylem and phloem.” Unlike most other essential elements, potassium does not become part of the plant, hence its high mobility.

Deficiency symptoms of mobile elements are first observed in older tissue, whereas toxicity is observed first in younger tissue.

Potassium deficiency symptoms in cucumbers
Potassium deficiency symptoms appear first in the lower or older leaves (this is an important diagnostic feature to remember). Older leaves show cupping, crinkled tissue within the veins, and chlorotic margins (Figure 1). Symptoms advance with chlorosis from the margins towards the area between the veins as yellow speckles, further resulting in interveinal chlorosis. Fruit presents abnormal growth, brown spots, and spongy-like texture.

Figure 1. Early stages of potassium deficiency on cucumbers grown in hydroponics systems. 1A. Young plants showing marginal chlorosis in the older leaves. 1B. Cucumber leaf showing marginal chlorosis, crinkled tissue within the veins, leaf cupping, and tip burn. 1C. Cucumber leaf curling and marginal chlorosis.

When identifying nutrient disorders, growers must pay attention to the location of the symptoms and the overall complex of signs. For example, cupping of younger leaves is a symptom of calcium deficiency, however calcium deficiency does not result in marginal chlorosis.

Interveinal chlorosis in younger leaves is a symptom of iron deficiency. Interveinal chlorosis of older leaves (similar to K deficiency) is a symptom of magnesium deficiency - however this deficiency does not include leaf cupping or puckering.

Additional indicators of the problem include knowing the crop’s tendency to a problem and nutrient levels in the tissue, the growing media, or nutrient solution.

Sonnevelt and Voogt (2009) suggested that the optimum K levels in young fully-grown leaves should be between 3.1-3.9%.

Read the full e-Gro Alert here.

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