**2. Objectives**

the development of the plants. Vegetables come from the most diverse regions of the world, from arid and desert regions up to the most humid tropical forests, from the icy north to the calico equator, from the sea level to the top of the mountain ranges, and from America

46 Potassium - Improvement of Quality in Fruits and Vegetables Through Hydroponic Nutrient Management

The protected cultivation consists of a technique that allows certain control of climatic variables like temperature, humidity of the air, solar radiation, and wind. This control translates into a gain in productive efficiency, reduces the effect of seasonality, favoring a more balanced supply over the months; in addition, the use of this technology allows the effect of seasonality to decrease. This benefit is most evident in regions with a cold climate, as the heat accumulated inside the greenhouses makes it possible to produce certain crops out of season and

The production of vegetables in this type of environment in Brazil is not so recent. In the 1980s, when the production of vegetables began, it was found that, after 3 years of cultivation, many producers could no longer obtain the productivity nor the quality obtained at the beginning of cultivation. At the time, the producers suffered from damages caused by inadequate practices resulting from lack of information and adequate technical assistance. This and other occurrences reinforced the myth that protected cultivation was not feasible. The advance of research, however, showed that the problem was not the system in use but the

In countries where protected cultivation is in an advanced stage, the nutritious solution is being replaced by different substrates, with the main objective of circumventing adverse phytosanitary and nutritional factors, allowing strict control of the root environment, especially in relation to water and nutrient management. One of the ways to work around problems of nutritious solution contamination is the use of hydroponic farming systems, in which nutrients are supplied by means of an aqueous solution containing all essential chemical elements

The main feature of the fertilizers used in hydroponics is that they are soluble in water. One should keep in mind the importance of chemical compatibility between different fertilizers. Macro- and micronutrients are used that are diluted in water to compose up the nutrient

In Brazilian agriculture, potassium (K) is the second nutrient most extracted by vegetables, after phosphorus, which is the nutrient most consumed as fertilizer. The permeability of the plasma membrane makes K to be easily absorbed and transported at long distance by xylem and phloem. Much of the total K of the plant is in the soluble form; therefore, its redistribution is facilitated in the phloem. Thus, under conditions of low K supply through the medium, the element is redistributed from the older leaves to the younger leaves and then transferred to the growing regions. The main biochemical function of K in the plant is enzymatic activation; more than 50 enzymes are dependent on K for their normal activity, such as synthetases, oxidoreductases, dehydrogenases, transferases, and kinases. For leaf and fruit vegetables, several

to Asia.

shorten the production cycle.

management adopted.

to the vegetables.

solution.

This chapter aims to present the cultivation of vegetables and fruits, their nutrient management in hydroponics and salinity condition, and the role of potassium fertilization on the physiological, biochemicals, and antioxidative quality of vegetables and fruits.
