Potassium participates in many physiological processes, such as growth, movement, transmission of signals, the upkeep of turgor pressure, and reproduction. Therefore potassium deficiency causes a variety of dysfunctions in plants’ metabolic processes which result in decreased productivity and quality of the crop yield.

Potassium deficiency in plants does not always immediately manifest itself in visible symptoms. Frequently at the initial stage potassium deficiency only reduces the growth and development rate of the plant also known as “hidden hunger.” Visible symptoms appear at advanced stages in the forms of chlorosis and necrotic spots. Given that in K-deficient plants potassium is transported from older leaves and organs to younger ones it is on the former that visible symptoms of potassium deficiency are observed in the first place.

Rice

Potash deficiency in rice can be identified by a number indicators, such as stunted plants with dark green leaves and short thin stems, rusty-brown spots that start at the tip and later spread over the entire area of the leaf, dry tips and margins of leaves, and a high percentage of rotten roots. In addition, under conditions of high temperatures and low humidity potash deficiency may cause premature senescence of older leaves and rolled-up younger leaves. Finally, the lack of potassium can results in a high percentage of sterile or unfilled grains.

Soya

Soy plants growing on potassium-poor soils are known to be commonly affected by potassium deficit. First the margins of leaves turn yellow, then the yellowing spreads inwards. The centre and base of the leaf remain green. If the K-deficiency is not addressed in a timely manner, chlorotic areas of the leaves extend into interveinal areas giving the leaf a “fishbone” pattern. Symptoms usually first appear on older leaves. If the problem of K-deficit is not addressed the leaf margins eventually die.

Wheat

Symptoms of potassium deficiency in wheat crops first appear on lower leaves progressing towards the top as the severity of the deficiency progresses. A deficit of potassium result in discoloration of tips and margins of wheat leaves as they turn yellow and brown.

As in other cereal crops, lack of potassium in wheat often causes the weakening of the straw which may result in lodging.

Maize

Leaves of maize plants suffering from potassium deficit turn yellow at tips and edges, then brown, then the discoloration affects the entire leaf and it dies. In sections, nodes are deep brown, different from internodes.

Potassium deficient plants soon show signs of wilting under dry conditions; grain formation is depressed and the tip of the ear may be without grain.

Sugarcane

Older leaves of K-deficient plants are affected with chlorosis and necrotic lesions at their tips and along their margins. The upper surface of the midrib discolors to red.

Sunflower

Sunflower plants suffering from potassium deficit have thinner and more brittle stems. The deficiency of potassium reduces yield and oil content, as well as negatively affects the ratio of unsaturated/saturated fat acids. Plant growth is significantly impeded by potassium-poor soils. Younger leaves of K-deficient sunflower plants are arranged in a rosette-like pattern and eventually develop dark brown necrotic patches. Ample application of potassium fertilizers may prevent these problems from occurring.

Potato

Among the first visible symptoms of potassium deficiency in potato plants are their reduced growth, reduced flowering, and bluish-green foliage. As the potash deficiency grows plant internocles become shortened, leaves bend downward and turn yellow, and eventually necrotic patches appear on their surface.

The color of potato crisps can be improved by potash fertilizers. Crisps made from potatoes which have been grown with ample application of potash fertilizers (left) are bright golden brown.

Cotton

In plants the K+ ion is mobile. When it is deficient it tends to move from older leaves to newer ones, therefore, the first visual symptoms of potassium deficiency can be identified by yellowish-white mottling of older leaves which later changes to light yellowish-green. Leaves develop yellow spots between veins, their centers die, and numerous brown spots develop at tips and margins between veins. Tips and margins tend to curl downwards. Eventually leaves become reddish-brown and dry and fall off prematurely, cotton balls are developed improperly and lint is of poor quality.