Functions of K :- Visual symptoms :- Predisposing factors:- Corrective measures :- Potassium (K+) is a univalent cation whose uptake is highly selective and coupled to metabolic activity. It is characterized by high mobility in plants at all levels. Potassium is the most abundant cation in the cytoplasm and potassium salts make a major contribution to the osmotic potential of the cells and tissues. Potassium functions in pH stabilization, osmoregulation, enzyme activation, protein synthesis and membrane transport. K+ is the predominant cation to charge balance of immobile anions in the cytoplasm and mobile anions in vacuoles and in conducting tissues. The role of K+ in the cation-anion balance is also reflected in nitrate metabolism in which K+ often is the predominant counter ion for NO3- in xylem and in vacuoles. Potassium improves the leaf colour, texture, combustibility and hygroscopic properties tobacco cured leaf. Potassium is the principal constituent of ash and is important in certain enzyme systems. Tobacco is known as luxury user of potassium. Flue cured tobacco grown in Northern light soil area requires fairly higher dose of potassium and in these soils, potassium deficiency was observed due to lower doses or no application of potassium. Higher leaf potassium reduces tar and other harmful substances in the smoke. When potassium is deficient, growth gets retarded and it is translocated from mature leaves and stems to younger leaves resulting in chlorosis coupled with appearance of necrotic symptoms on older leaves. When the soil water supply is limited, loss of turgor and wilting are typical symptoms of potassium deficiency. Due to K deficiency leaves became cup shaped from the underside. Lower leaves showed typical mottling and chlorosis at tips and margins. The mottling appears to progress rapidly from the lower to the upper leaves. Potassium deficiency is common in sandy soils because potassium ions are highly soluble and easily leaches from soils. It is also found in heavy clays with poor structure. In tobacco K deficient symptoms are seen due to excess nitrogen application also. Potassium deficiency symptoms can be corrected by soil application of recommended potassium fertilizers to tobacco crop or through foliar application of potassium salts.

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