Potassium

Amber Anderson

Learning Objectives
  • Identify the function of potassium in the plant and potential deficiency symptoms.
  • Define the concept of “luxury consumption”
  • Identify under what conditions potassium deficiencies might be more likely

Row of corn plants that are brown at the bottom of the stalk that shifts to yellow and then green as the plant height increases.

Role in the plant

Potassium is contained in the sap rather than structural components of the plant. It is involved in water regulation, such as stomata opening and closing, as well as some enzymatic and energy reactions within the plant. Because of this function, deficiency symptoms may be more evident in hot and dry growing seasons.

Potassium cycle

Illustration of the potassium cycle. An arrow captioned "mining" points to a gray cylinder labeled fertilizer. There is an arrow pointing away from fertilizer that says "application" pointing to rows of corn. An arrow pointing from the sky to the corn is labeled precipitation. There is a double ended arrow pointing between atmosphere and corn. the is an arrow pointing from the ground to a corn plant captioned "uptake". There is an arrow pointing away from a corn plant labeled "decay". There is an arrow pointing from a corn plant in the ground to harvested corn plant labeled "crop harvest". There is an arrow from the soil pointing towards the lithosphere captioned "erosion, sedimentation, lithification". An arrow point from the lithosphere to the soil labeled "weathering". Cycle within soil showing movement between exchangable K , fixed K, and solution K with double ended arrows. There is an arrow from the soil to the hydrosphere labeled "leaching, erosion". There is an arrow from the hydrosphere to the lithosphere labeled "absoprtion, deposition, evaporation, subduction". There is an arrow from the hydrosphere to the atmosphere labeled "marine aerosols". There is an arrow from the atmosphere to the hydrosphere captioned "precipitation".
Potassium cycle illustrated. Image Source: Compost Camel, CC BY SA

The primary location of potassium in soils are the primary minerals. Small amounts are held on the cation exchange capacity, and significantly less of that is available to the plant in the solution at one time. If the soil can’t supply potassium, fertilizer application would be required. Historically, materials like ‘pot-ash’, or ash from burned materials would be used for potassium enrichment.

Soybean plant with leaves that have yellow discoloration along the edges.
Potassium deficiency on soybean

Luxury consumption

Luxury consumption is the concept of plant uptake beyond plant needs. If the crop is harvested for grain, this may not be a significant issue. However, if a forage like alfalfa, or silage is produced, this would result in a higher export of potassium from the soil.

Deficiency symptoms

Deficiencies in potassium may be found in areas where the entire plant is removed, while green.

 

Potassium and forage management:

 

Key Takeaways
  • Potassium is important in water regulation within the plant
  • Risk of potassium deficiency increases in areas where plants are harvested green and removed
  • Symptoms may be more evident in hot and dry years
  1. https://www.soils.org/news/science-news/alfalfa-and-potassium-its-complicated/ ↵

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Introduction to Soil Science Copyright © 2023 by Amber Anderson is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.