Potassium (K) is one of the essential nutrients and is taken up in significant amounts by crops. Potassium is vital to photosynthesis, protein synthesis and many other functions in plants. It’s classified as a macronutrient, as are nitrogen (N) and phosphorus (P). Plants take up K in its ionic form (K+).

Quick Facts

Potassium enhances many enzyme actions aiding in photosynthesis and food formation. It builds cellulose and helps translocate sugars and starches. Potassium is vital to producing grains rich in starch.

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Potassium maintains turgor and reduces water loss and wilting.

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Potassium is known as the "quality nutrient" because of its important effects on factors such as size, shape, color, taste, shelf life, fiber and other quality-related measurements.

Quick Facts

In many high-yielding crops, the K content in the plant is comparable to the nitrogen (N) content.

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Potassium is absorbed by plants in the ionic form, indicated as K+.

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Plants deficient in K are less resistant to drought, extreme temperatures and other stressors. Plants lacking K are also more susceptable to pests, diseases and nematode attacks.

Quick Facts

Ample K can increase root growth and improves drought tolerance.

Dig Deeper

Potassium is essential in nearly all processes needed to sustain plant growth and reproduction. Plants deficient in potassium are less resistant to drought, excess water, and high and low temperatures. They are also less resistant to pests, diseases and nematode attacks. Because potassium improves the overall health of growing plants and helps them fight against disease, it is known as the "quality" nutrient. Potassium affects quality factors such as size, shape, color and vigor of the seed or grain, and improves the fiber quality of cotton.

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While potassium doesn’t constitute any plant structures or compounds, it plays a part in many important regulatory roles in the plant. It’s essential in nearly all processes needed to sustain plant growth and reproduction, including:

  • photosynthesis
  • translocation of photosynthates
  • plant respiration
  • protein synthesis
  • control of ionic balance
  • breakdown of carbohydrates, which provides energy for plant growth
  • regulation of plant stomata and water use
  • activation of plant enzymes
  • disease resistance and recovery
  • turgor
  • stress tolerance, including extreme weather conditions

Perhaps potassium’s most important function in the plant is that it can activate at least 80 enzymes that regulate the rates of major plant growth reactions. Potassium also influences water-use efficiency. The process of opening and closing of plant leaf pores, called stomates, is regulated by potassium concentration in the guard cells, which surround the stomates. When stomates open, large quantities of potassium move from the surrounding cells into the guard cells. As potassium moves out of the guard cells into surrounding cells, stomates close, therefore potassium plays a key role in the process plants use to conserve water Potassium plays a key part in increasing yields and controlling disease because it improves a crop’s winter hardiness. It enables crops to get a quicker start in the spring and increases vigor so growth can continue throughout the growing season. Plants deficient in potassium don’t grow as robustly and are less resistant to drought, as well as high and low temperatures. They’re also more vulnerable to pests, diseases and nematode attacks. Potassium is also known as the “quality nutrient” because of its important effects on factors such as size, shape, color, taste, shelf life, fiber quality and other qualitative measurements.

Dig even deeper into Potassium

Source: Soil Fertility Manual (2006) by the International Plant Nutrition Institute (IPNI) and the Foundation for Agronomic Research (FAR).

Deficiency Symptoms

Symptoms of deficiency can vary across crop species, but similarities exist for how nutrient insufficiency impacts plant tissue color and appearance. Nutrient deficiencies are commonly associated with the physical location on the plant (i.e., whether the symptoms are primarily observed on older versus newly formed plant tissue), but these symptoms can spread as the severity of the deficiency progresses.

All photos are provided courtesy of the International Plant Nutrition Institute (IPNI) and its IPNI Crop Nutrient Deficiency Image Collection. The photos above are a sample of a greater collection, which provides a comprehensive sampling of hundreds of classic cases of crop deficiency from research plots and farm fields located around the world. For access to the full collection, you can visit IPNI's website.