Potassium Deficiency in Tomato
Symptoms are mainly visible on older leaves and only affect young leaflets in extreme cases. Mild potassium deficiencies are characterized by the development of a marginal yellow chlorosis at the edge of leaves (tip burn). Whitish, necrotic dots can appear within these chlorotic areas. In severe cases, these patches turn into dry, leathery tan scorches (necrosis) that gradually progress from the leaf edge to the midrib. The main veins remain green and the leaves tend to curl and crinkle. Plants have woody stems and growth is stunted. Flowering and fruiting are compromised. If the deficiency happens during fruit development, tomatoes show a blotchy ripening, with some areas remaining green, most commonly near the stalks.
Deficiencies occur because of low reserves of potassium in the soil or limited availability to the plant. They can be observed in acidic soils. Heavy irrigation and high rainfall wash the nutrients from the root zone and can lead to deficiencies. Drought conditions, in turn, block the transport of water and nutrients to the plants. Sandy or light soils with little organic content are prone to nutrient leaching and drought, and may therefore cause problems. Potassium plays a essential role in the transport of water, the firmness of tissues and the exchange of gases with the atmosphere. Potassium-deficient plants become more susceptible to drought, frost stress and disease.
Add organic matter in the form of animal manure 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 are available in the market. The most widely used product is potassium chloride. Other mineral fertilizers include potassium nitrate, potassium sulfate, and monopotassium phosphate.