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Symptoms are mainly visible on older leaves and start to develop on young leaves only in case of severe deficiencies. Mild potassium deficiencies are characterized by the development of a mild chlorosis at the margins and tips of the leaves, later followed by tip burn. The leaf blade turns somewhat paler but the main veins remain dark green (interveinal chlorosis). If not amended, these chlorotic patches turn into a dry, leathery tan or dark brown scorch (necrosis) that usually progresses from the leaf edge to the midrib. However, the main veins tend to remain green. Leaves tend to curl and crinkle and often collapse prematurely. Young leaves remain small and dull, assuming a cupped appearance. Potassium-deficient plants grow stunted and are more susceptible to diseases and other stresses such as drought and frost. In some cases, fruits may be severely deformed.
Deficiencies may occur because of low reserves of potassium in the soil or limited availability to the plant. Soils with low pH and sandy or light soils with little organic content are prone to nutrient leaching and drought, and may therefore cause problems. Heavy irrigation and high rainfall wash the nutrients from the root zone and can also lead to deficiency. Hot temperatures or drought conditions block the transport of water and nutrients to the plants. High levels of pand start to develop on young leaves only in case of severe deficiencies. Mildhosphorus, magnesium and iron can also compete with potassium. Potassium plays a essential role in the transport of water, the firmness of tissues and the exchange of gases with the atmosphere. The symptoms of potassium deficiency are irreversible, even if potassium is later added to the plants.
Add organic matter in the form of ashes or plant mulch to the soil at least once a year. Wood ash also has high potassium content. Liming acidic soils can increase potassium retention in some soils by reducing leaching.
A variety of potassium fertilizers is available in the market. The formulation of the potassium applied can play an important role in quality and yields. The most widely used product is potassium chloride. Other mineral fertilizers include potassium nitrate, potassium sulfate, and mono-potassium phosphate. Potassium fertilizers should be incorporated in the soil before planting. A soil test can be used to determine the rate needed. Foliar sprays seem to be less effective and can burn leaves.