The role of potassium is directly related to the quality and production. The increment of the potassium levels improves the plant performance.
The essential roles of potassium are found in the protein synthesis, the photosynthetic processes and the sugars transport from the leaves to the fruits. A good potassium supply will sustain, therefore, from the beginning the leaf function in the fruit growing. This will contribute to the positive potassium effect in the plant yield and in the higher soluble solids´ content (more sugar) in the fruit at harvest time. Approximately 60 to 66% of the potassium absorbed by the plant is found in the fruit (Winsor et al, 1958). The potassium action in the protein synthesis reinforces the conversion of the nitrate absorbed in proteins, contributing to better efficiency of the supplied nitrogen fertilizer. Potassium is a cation involved in the maintenance of the plant osmotic potential (cell turgidity). An implication of this is the stoma movement; when stomata are open allow the plants to exchange gas and water with the atmosphere. This permits the plants to maintain an adequate hydration under stress conditions such as salinity or water shortage. In fact, the tomato crop with a high content of potassium generally shows a greater efficiency in the water use, this means, that this consumes relatively less water than potassium deficit crops for producing the same biomass quantity. In addition, potassium is involved in the fruit maturity processes such as the synthesis of the licopene pigment, which is responsible of the tomato red color. Potassium promotes a high acid content, which is essential for the good fruit flavor.