**Potassium Nutrition in Fruits and Vegetables and Food Safety through Hydroponic System Safety Through Hydroponic System**

**Potassium Nutrition in Fruits and Vegetables and Food** 

DOI: 10.5772/intechopen.71742

Flávio José Rodrigues Cruz, Renato de Mello Prado, Guilherme Felisberto, Águila Silva Santos and Rafael Ferreira Barreto Flávio José Rodrigues Cruz, Renato de Mello Prado, Guilherme Felisberto, Águila Silva Santos and Rafael Ferreira Barreto Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.71742

#### **Abstract**

Although it is not an element with structural function in plants, potassium (K) is demanded in considerable quantities by plants due to multifunctional role in plant physiology and metabolism. Nevertheless, the interface of plant mineral nutrition and food safety evidences needs for a better understanding of functional mechanisms of this nutrient in plants, taking into account its management in hydroponic cultivation and food production with nutritional quality. Thus, the nutritional content of K in vegetables is indicative of post-harvest and nutritional quality. This fact is important considering that modern life has induced increased consumption of processed foods whose preparation implies reduction of K levels and increase of Na levels, with the consequent low K intake and appearance of diseases related to insufficient intake. Therefore, the present chapter aimed to address main nutritional, physiological, and biochemical aspects of K in a context of hydroponic plant production and importance of potassium nutrition to human health.

**Keywords:** K, plant nutrition, transport of K, food, metabolism

#### **1. Introduction**

The term "potash" describes a variety of extracted and manufactured salts containing chemical element potassium (K) in water-soluble form. It is one of three primary nutrients for plants, along with nitrogen and phosphorus, with about 90% potash being used in the production of fertilizers [1]. The K, abbreviation of word neo-latina *kalium* (derived from "alkali," latinized form of Arabic *al-qali* which means calcined ash), was isolated like an element by Humphry

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

Davy in 1807, but its compounds were already used in processes known from ancient times [2]. From the chemical point of view, K belongs to alkali metal family, being a univalent ion ray cation of 0.331 nm and hydration energy of 314 mols−1 [3].

In fact, there is a close relationship between plant nutrition and food safety, considering potassium nutrition interface of vegetables and human health, since one of the conditions for safe food is the production and availability of foods with nutritional quality [20]. Thus, good management of vegetable nutrition can contribute not only to gains in productivity and postharvest quality but also to people's quality of life through the ingestion of healthy foods rich

Potassium Nutrition in Fruits and Vegetables and Food Safety through Hydroponic System

http://dx.doi.org/10.5772/intechopen.71742

25

Coincidently, one of the most important mineral nutrients for human health is K; from physiological point of view it plays an important role in the conduction of electrical impulses by cells of nervous system, muscle contraction, and vascular functioning [21]. There are several food sources that can satisfy human needs of K, such as vegetables of its accessibility, low cost to consumer, and easy nutritional management. However, the production of vegetables in quantity and quality in hydroponic system is closely linked to nutritional management, especially of potassium nutrition, given the great importance of this nutrient in physiology and post-harvest quality of plants of food interest. The present chapter aimed to address the main aspects of potassium nutrition of vegetables and fruits, emphasizing the importance of

In hydroponic cultivation, the supply of K is carried out from fertilizers containing this element, which have considerable amounts of other nutrients as accompanying ions (**Table 1**). Thus, the choice of source depends on factors such as availability, commercial value, the requirement of culture by accompanying ion, and saline index. However, it is important that more than one source is available to facilitate the equilibrium of final concentration of K in

**Fertilizer Formula Nutrient Concentration (%) Solubility (g L−1 at 20°C)**

N-NO3

<sup>−</sup> 13

P 23

S 18

Cl 48

PO4 K 28 226

SO4 K 45 111

interface plant nutrition and food safety in hydroponic farming system.

culture solution, which depends on the requirement of each culture.

Potassium nitrate KNO3 K 38 316

Potassium chloride KCl K 60 330

**Table 1.** Fertilizers containing potassium that is commonly used in the preparation of nutrient solutions.

**2. Source of potassium fertilizers**

Monopotassium phosphate KH2

Potassium sulfate K2

Source: [19]

in mineral nutrients.

The K is an essential macronutrient and one of the most important cations in higher plants, constituting about 2–10% of the mass of the dry matter [4]. The K is essential for enzyme activation, protein synthesis, and photosynthesis, as well as modulating osmotic regulation during cell expansion, stomatal movements and tropism [5], and transport of photoassimilates of fabrics sources for fabrics drains [3]. The cytoplasmic concentration of K in plant cells is estimated to be around 100 mM (40–200 mM). This concentration of K appears to be relatively stable, with an optimal concentration of K for enzymatic activity [6]. On the other hand, the concentration of K in the soil is low, being in micromolar range of 0.1–1 mM [7].

The absorption of K is performed by means of three groups of membrane proteins, the permeases (KT/HAK/KUP), transporters (Trk/HKT), and by proteins of cation-type antiporter (CPA) [8]. Electrophysiological studies have shown that under K millimolar concentrations, K absorption occurs passively through ion channels and actively through H+−cotransporters when the K concentration is in the micromolar range [9, 10]. When K concentration in the soil solution is below 0.2 mM, high-affinity absorption mechanisms are activated; on the other hand, when K concentrations are above 0.3 mM, mechanisms of low-affinity absorption are activated [9, 11, 12].

In plants, K is characterized by great mobility, being easily transported to aerial part or even redistributed among various organs of plants. Due to considerable number of functions performed by K in plants, this macronutrient plays an important role in plant growth and development, as well as food quality.

Adequate potassium nutrition is associated with increased fruit production, fruit size, soluble solids increase and ascorbic acid concentration, fruit color improvement, fruit shelf life, and supermarket shelf life [13–16]. Additionally, K is involved in post-harvest quality of vegetables and fruits; it is considered a nutrient associated with quality of products of plant origin due to its important effects on post-harvest attributes such as color, size, acidity, resistance to transportation, handling, storage, nutritional value, and industrial qualities [17, 18].

One of strategies of high-quality food production is the adoption of hydroponic system of cultivation, in which the control of plant nutrition (i.e., concentration of nutrients, pH, and electrical conductivity of nutrient solution) and growing environment (i.e., temperature, luminosity, and humidity) are more effective in obtaining high-quality vegetables compared to field cultivation. Hydroponic vegetable production has increased significantly in recent years worldwide, allowing more efficient use of water and fertilizers, as well as better control of climatic and phytosanitary factors. In addition, hydroponic production increases the quality and productivity of vegetables, resulting in competitiveness and profitability [19].

In fact, there is a close relationship between plant nutrition and food safety, considering potassium nutrition interface of vegetables and human health, since one of the conditions for safe food is the production and availability of foods with nutritional quality [20]. Thus, good management of vegetable nutrition can contribute not only to gains in productivity and postharvest quality but also to people's quality of life through the ingestion of healthy foods rich in mineral nutrients.

Coincidently, one of the most important mineral nutrients for human health is K; from physiological point of view it plays an important role in the conduction of electrical impulses by cells of nervous system, muscle contraction, and vascular functioning [21]. There are several food sources that can satisfy human needs of K, such as vegetables of its accessibility, low cost to consumer, and easy nutritional management. However, the production of vegetables in quantity and quality in hydroponic system is closely linked to nutritional management, especially of potassium nutrition, given the great importance of this nutrient in physiology and post-harvest quality of plants of food interest. The present chapter aimed to address the main aspects of potassium nutrition of vegetables and fruits, emphasizing the importance of interface plant nutrition and food safety in hydroponic farming system.
