**4. Hydroponic nutrient management for improving quality of fruits and vegetables**

Hydroponic nutrient solution contains mainly inorganic soluble salts of essential elements for higher plants. Each essential element has a clear physiological role, and its absence prevents the plant from normal growth and development [20]. Mineral composition in nutrient solution determines different chemical properties such as pH, electrical conductivity, and osmotic potential that affect uptake by plants. In general, hydroponic nutrient solution contains sufficient amount of essential nutrient for luxurious uptake by plant roots. If it is applied continuously, plants can uptake essential ions at very low concentrations. Therefore, researchers reported that higher concentrations of mineral nutrients are not used by plants or their uptake does not impact the higher production. It has been shown that the concentration of nutrient solution can be reduced by 50% without any adverse effect on biomass and quality in gerbera [21] and geranium [22].

Most of the researchers suggested that adequate potassium nutrition increased yields and yield attributes especially size and shape, improved qualities such as soluble solids contents, ascorbic acid concentrations, fruit color, shelf life, and also shipping quality of many horticul-

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

Potassium concentration affects the sodium levels in the growing medium of plants. In general, antagonistic interaction exists in between potassium and sodium uptake by plants. However, the synergistic or antagonistic effect between them depends on the amount of each element present in the soil and on the plant type [12]. Under saline condition, plants preferably uptake sodium instead of potassium. While in sodium salinity condition, plant uses more selective high-affinity system for potassium uptake in order to maintain adequate potassium nutrition. Several studies showed the antagonistic effects of potassium and sodium in corn [13], rice [14], faba bean [15], and tomato [14]. It is also reported that adverse effect of sodium on plant growth is attributed to its antagonistic relationship with calcium, potassium, and

It is inevitable that reduced potassium supply will inhibit plant growth and yield. Therefore, investigation on minimal requirements of potassium in plants maintaining their normal growth and development is necessarily important. Recent research reported that low potassium concentration in the nutrient solution significantly decreased the fruit potassium content in netted melon [16]. In leafy vegetables and tomato, sodium and magnesium content found to be increased significantly when potassium content was restricted to the culture

Research results also showed that decrease in potassium levels increase the concentration of sodium and magnesium in tomato fruits [18, 19]. Sodium concentration in melon fruit increased with the decrease of potassium concentration in the nutrient solution and its concentration increase to 56% compared to standard concentration when plants were cultured

**4. Hydroponic nutrient management for improving quality of fruits** 

Hydroponic nutrient solution contains mainly inorganic soluble salts of essential elements for higher plants. Each essential element has a clear physiological role, and its absence prevents the plant from normal growth and development [20]. Mineral composition in nutrient solution determines different chemical properties such as pH, electrical conductivity, and osmotic potential that affect uptake by plants. In general, hydroponic nutrient solution contains sufficient amount of essential nutrient for luxurious uptake by plant roots. If it is applied continuously, plants can uptake essential ions at very low concentrations. Therefore, researchers

**3. Interaction of potassium with other nutrients**

without potassium fertilizer from anthesis to harvest [16].

tural crops [7–11].

zinc in plants [13].

solution [17].

**and vegetables**

In another study, no adverse effect on growth, fruit yield, and fruit quality in tomato was reported when there is reduction of macronutrient concentrations to 50% of the control level [23]. High levels of potassium in the nutrient solution increased fruit dry matter, total soluble solid content, and lycopene concentration of tomato [24]. Recent studies showed that reduced KNO3 concentration in standard hydroponic nutrient solution produced melon fruits with lower potassium content [16].
