Source. Source of K⁺ to the plants is inorganic compounds like potassium sulphate, potassium nitrate etc. Potassium is usually present in sufficient amount in clay soils, where it is firmly bound. It is prevalent cation in plants and may be involved in the maintenance of ionic balance in cells. It contains approximately 0.3 to 6.0 percent of whole plant. In seeds, it is found in less amount.

Regions. It is required in meristematic and differentiating tissues. Potassium accumulates in older leaves.

Functions. Potassium appears to have no structural role in plants, but it serves a number of catalytic roles. Deficiency in potassium affects physiological processes like respiration, photosynthesis and chlorophyll development. It helps in determination of anion cation balance in cells. It is involved in protein synthesis. Potassium takes part in the formation of cell membrane and opening and closing of stomata. It increases hardness and activates enzymes. It is also responsible for maintenance of turgidity of cells. It is considered that whole of potassium in plant is found in soluble form and most of it is contained in cellsap and cytoplasm.

Deficiency symptoms

(i) Yellow edges in leaved appear.
(ii) Premature death.
(iii) Chlorosis followed by necrosis at the tip and margins of leaves.
(iv) Widespread blackening or scorching of leaves may occur as a result of increased tyrosinase activity.
(v) Rosette or bushy habit of growth may be seen in plants.
(vi) Reduction of stem growth, weakening of stem.
(vii) Lowered resistance to pathogens.
(viii) The color of the leaf may become dull or bluish green.