**2. Potassium nutrition in plants and its interactions with other nutrients in hydroponic culture**

#### **2.1. Hydroponic nutrient solution commonly used for plant**

In hydroponic culture, nutrient solutions are the only source of plant nutrition. A solution containing all the plant nutrients must be applied in the correct balance. For the selection of fertilizers and preparation of hydroponic nutrient solutions, the following factors should be considered:

**1.** Concentration of harmful elements such as sodium, chloride and boron, salinity and water quality should be considered.


In **Table 1**, it is shown common nutrient ranges in the hydroponic nutrient solutions. **Table 2** shows the recommended nutrient solutions for various plants [6].

Total salts dissolved in the hydroponic nutrient solution are considered as a measure of **electrical conductivity (EC)**. EC is a parameter used to follow the fertilization process. EC-related data do not reflect the mineral content of the nutrient solution.

The cation exchange capacity (CEC) is the cornerstone of hydroponic nutrition. The effect of potassium cation in cation exchange capacity is indisputable. The cation exchange provides

**Crop N P K Ca Mg**

Potassium Nutrition in Plants and Its Interactions with Other Nutrients in Hydroponic Culture

Tomato 190 40 310 150 45 Cucumber 200 40 280 140 40 Pepper 190 45 285 130 40 Strawberry 50 25 150 65 20 Melon 200 45 285 115 30 Roses 170 45 285 120 40

phosphate/potassium sulfate, potassium nitrate, potassium phosphate, and ammonium

**3.** The cation exchange helps to provide micronutrient trace metals such as Zn2+ and Mn2+ in

**4.** The cation exchange provides resistance to **the changes in pH** as well as maintaining plant

In **Figure 1**, the cation exchange capacities on the surfaces of clay particles and organic materi-

Mo and Mg are present at higher pH than most nutrients. On the other hand, trace metals such as Fe, Zn, and Mn are found at a lower pH than most nutrients. The ideal pH value for many plants is about 5.8 to 7.0. The values in this range are a balanced source for all nutrients [6].

The hydroponic nutrient solution should be checked frequently. This process provides information about the time of replacement of the nutrient solution or the time of dilution with fresh water. **The ideal pH range** for hydroponic nutrient solution is 5.8–6.3. For many plants, the optimum pH range is shown in **Figure 2**. The pH value of the micronutrients is usually below the limit value. If the pH levels fall below 5.5, the risk of micronutrient toxicity and also the impairment of calcium and magnesium accelerate. In the closed system hydroponics, the influence of the roots on the pH value of the hydroponic solution is great. This causes pH fluctuation. Sulfuric acid, phosphoric acid, and nitric acid are used to increase the acid value of the hydroponic nutrient solution. One of the most important factors affecting **the pH value** 

als with negatively charged sites holding positively charged ions are compared.

**of the nutrient solution** is the addition of ammonium/nitrate.

(Monopotassium

+ ).

http://dx.doi.org/10.5772/intechopen.71951

13

**1.** The cation exchange is the major nutrient (macronutrient) reservoir of K+

**Table 2.** The necessary quantities of the elements found in the nutrient solution for various plants.

**2.** It is necessary to keep the nitrogen (N) in the form of ammonium (NH<sup>4</sup>

the following conditions:

**Concentration in mg/l (ppm)**

a certain amount.

nutrients.

phosphate), Ca2+, and Mg2+.

The hydroponic nutrient solution is recirculated in closed hydroponic systems. Thus, the elements (sodium, chloride, fluoride, etc.) that are not absorbed in high amounts by the plants or the ions released by the plant are deposited in the hydroponic nutrient solution. In this case, the electrical conductivity (EC) cannot provide information about the content of the nutrient solution.


**Table 1.** The common nutrient range values of the ionic form of the elements absorbed by plants.


**Table 2.** The necessary quantities of the elements found in the nutrient solution for various plants.

**2.** The concentration values of the necessary nutrients in the hydroponic nutrient solution

**4. The pH value of the hydroponic nutrient solution** should be considered and the effect of the pH value of the hydroponic nutrient solution on the uptake of nutrients by the plants

In **Table 1**, it is shown common nutrient ranges in the hydroponic nutrient solutions. **Table 2**

Total salts dissolved in the hydroponic nutrient solution are considered as a measure of **electrical conductivity (EC)**. EC is a parameter used to follow the fertilization process. EC-related

The hydroponic nutrient solution is recirculated in closed hydroponic systems. Thus, the elements (sodium, chloride, fluoride, etc.) that are not absorbed in high amounts by the plants or the ions released by the plant are deposited in the hydroponic nutrient solution. In this case, the electrical conductivity (EC) cannot provide information about the content of the nutrient

**(ppm = mg/l)**

30–50 ppm elemental P

) 100–250 ppm elemental N

) 0.2–0.5 ppm elemental B

**Element Ionic form absorbed by plants Common range** 

+

2−)

), phosphate (PO<sup>4</sup>

3−),

2−) 50–120 ppm elemental S

2−) 0.04–0.08 ppm

) <50 ppm TOXIC to plants

) <75 ppm

) 100–300 ppm

PO<sup>4</sup> −

Calcium Calcium (Ca2+) 80–140 ppm Magnesium Magnesium (Mg2+) 30–70 ppm

Iron Ferrous ion (Fe2+), ferric ion (Fe3+) 1–5 ppm Copper Copper (Cu2+) 0.04–0.2 ppm Manganese Manganese (Mn2+) 0.5–1.0 ppm Zinc Zinc (Zn2+) 0.3–0.6 ppm

> BO<sup>3</sup> −

**3.** Nutrient balance should be provided in the nutrients that the plants receive.

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

shows the recommended nutrient solutions for various plants [6].

data do not reflect the mineral content of the nutrient solution.

−

monohydrogen phosphate (HPO<sup>4</sup>

BO<sup>3</sup>

), Borate (H<sup>2</sup>

**Table 1.** The common nutrient range values of the ionic form of the elements absorbed by plants.

), Ammonium (NH<sup>4</sup>

should be well adjusted.

should be investigated.

solution.

Nitrogen Nitrate (NO<sup>3</sup>

Potassium Potassium (K+

Sulfur Sulfate (SO<sup>4</sup>

Molybdenum Molybdate (MoO<sup>4</sup>

Boron Boric acid (H<sup>3</sup>

Chloride Chloride (Cl<sup>−</sup>

Sodium Sodium (Na+

Phosphorus Dihydrogen phosphate (H<sup>2</sup>

The cation exchange capacity (CEC) is the cornerstone of hydroponic nutrition. The effect of potassium cation in cation exchange capacity is indisputable. The cation exchange provides the following conditions:


In **Figure 1**, the cation exchange capacities on the surfaces of clay particles and organic materials with negatively charged sites holding positively charged ions are compared.

Mo and Mg are present at higher pH than most nutrients. On the other hand, trace metals such as Fe, Zn, and Mn are found at a lower pH than most nutrients. The ideal pH value for many plants is about 5.8 to 7.0. The values in this range are a balanced source for all nutrients [6].

The hydroponic nutrient solution should be checked frequently. This process provides information about the time of replacement of the nutrient solution or the time of dilution with fresh water. **The ideal pH range** for hydroponic nutrient solution is 5.8–6.3. For many plants, the optimum pH range is shown in **Figure 2**. The pH value of the micronutrients is usually below the limit value. If the pH levels fall below 5.5, the risk of micronutrient toxicity and also the impairment of calcium and magnesium accelerate. In the closed system hydroponics, the influence of the roots on the pH value of the hydroponic solution is great. This causes pH fluctuation. Sulfuric acid, phosphoric acid, and nitric acid are used to increase the acid value of the hydroponic nutrient solution. One of the most important factors affecting **the pH value of the nutrient solution** is the addition of ammonium/nitrate.

For this reason, the quality and content of the raw water should be tested before proceeding to the fertilizer formulation for fertilization. Trace elements such as boron, manganese, iron and zinc and minerals such as calcium, magnesium, and sulfur are likely to be present in the source water. Therefore, while the hydroponic nutrient solution is being prepared, the effect of these elements must also be taken into account. In addition, undesirable minerals such as sodium, chloride, or fluoride can be present in raw water. For the hydroponic nutrient solution, the presence of these minerals is undesirable. To get rid of such a situation, the following

Potassium Nutrition in Plants and Its Interactions with Other Nutrients in Hydroponic Culture

http://dx.doi.org/10.5772/intechopen.71951

15

The overturning and pumping of the nutrient solution can be expressed as tank exchange operations. These operations are done at a certain time/frequency. Tank exchange is one of the factors that can be controlled in hydroponic systems. There are many different ways to save time during tank exchange. One of these is the addition of a small amount of nutrient concentrate to the most consumed nutrient ions. In general, N, K, and P constitute the content of the added nutrient concentration. In a previous study, the content of daily-added nutrient

The addition of source water and calcium nitrate causes the Ca ion to increase in some solutions. To avoid Ca addition, potassium nitrate and monopotassium phosphate are added to fertilizer materials. In addition, if the addition of potassium nitrate and monopotassium phosphate can limit the Ca value in solution, fertilization formulations are regulated by a lower Ca starting value. The nutrient tank change test provides information on how the additions of nutrients compare to tank change in normal and low calcium nutrient formulations. Researchers conducting such a test could form four different nutrient solutions. These are

concentrate was applied as 10 ppm for N and P and 15 ppm for K [7].

The researchers noted the following perspectives in their work:

additions were made after the tank change.

additions were made after the tank change [7].

**1.** During the production, a tank change was made in the normal solution.

**3.** During the production, a tank change was made in the low calcium solution.

**2.** There is no tank change in the normal solution. In further treatment, daily KNO<sup>3</sup>

**4.** There is no tank change in low calcium solution. In further treatment, daily KNO<sup>3</sup>

and

and

**2.2. Interactions of potassium with other nutrients in hydroponic culture**

actions can be taken:

**2.** Raw water can be desalted.

**3.** Ion exchange is possible [6].

detailed in **Tables 3** and **4** [7].

KH<sup>2</sup> PO<sup>4</sup>

KH<sup>2</sup> PO<sup>4</sup>

**1.** Raw water can be diluted by adding pure water.

**Figure 1.** The appearance of the surfaces of clay particles and organic matter with negatively charged sites that hold positively charged ions.

**Figure 2.** The ideal pH range of the elements in the hydroponic nutrient solution used for most of the crop plants.

The minerals found in raw water and the nutrients supplied by fertilization are the two main factors that bring the hydroponic nutrient solution. The quality of the raw water greatly affects the choice of fertilizers and their concentration in the hydroponic nutrient solution. For this reason, the quality and content of the raw water should be tested before proceeding to the fertilizer formulation for fertilization. Trace elements such as boron, manganese, iron and zinc and minerals such as calcium, magnesium, and sulfur are likely to be present in the source water. Therefore, while the hydroponic nutrient solution is being prepared, the effect of these elements must also be taken into account. In addition, undesirable minerals such as sodium, chloride, or fluoride can be present in raw water. For the hydroponic nutrient solution, the presence of these minerals is undesirable. To get rid of such a situation, the following actions can be taken:


The minerals found in raw water and the nutrients supplied by fertilization are the two main factors that bring the hydroponic nutrient solution. The quality of the raw water greatly affects the choice of fertilizers and their concentration in the hydroponic nutrient solution.

**Figure 2.** The ideal pH range of the elements in the hydroponic nutrient solution used for most of the crop plants.

**Figure 1.** The appearance of the surfaces of clay particles and organic matter with negatively charged sites that hold

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

positively charged ions.

The overturning and pumping of the nutrient solution can be expressed as tank exchange operations. These operations are done at a certain time/frequency. Tank exchange is one of the factors that can be controlled in hydroponic systems. There are many different ways to save time during tank exchange. One of these is the addition of a small amount of nutrient concentrate to the most consumed nutrient ions. In general, N, K, and P constitute the content of the added nutrient concentration. In a previous study, the content of daily-added nutrient concentrate was applied as 10 ppm for N and P and 15 ppm for K [7].

#### **2.2. Interactions of potassium with other nutrients in hydroponic culture**

The addition of source water and calcium nitrate causes the Ca ion to increase in some solutions. To avoid Ca addition, potassium nitrate and monopotassium phosphate are added to fertilizer materials. In addition, if the addition of potassium nitrate and monopotassium phosphate can limit the Ca value in solution, fertilization formulations are regulated by a lower Ca starting value. The nutrient tank change test provides information on how the additions of nutrients compare to tank change in normal and low calcium nutrient formulations. Researchers conducting such a test could form four different nutrient solutions. These are detailed in **Tables 3** and **4** [7].

The researchers noted the following perspectives in their work:



**2.** There were no significant differences in tipburn ratings.

Thus, the accumulation of S in solution is also reduced.

initial values should be applied to avoid deficiencies [7].

nutrient solution contains substances above pH 7; Fe2+, Mn2+, PO<sup>3</sup>

to the salts. This means that the nutrients received by plants are restricted [9].

to change. Determination of increased Na levels in time is important.

frequent tank changes can do this.

eters should be examined.

by the addition of KNO<sup>3</sup>

monitored.

**3.** There was some variability in tipburn ratings among treatments. It is envisaged that less

Potassium Nutrition in Plants and Its Interactions with Other Nutrients in Hydroponic Culture

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17

**4.** The starting point of the solution conditions prepared by the producers should be closely

**5.** The relationship between the individual conditions in the source water and other param-

**6.** The most detrimental properties of the solution are the increase in S and Na content by the end of the process. In this case, it is necessary to lower the pH. For this, a nitric acid solution should be used instead of the sulfuric acid solution. Instead of increasing the K level

**7.** The effect of source water increases the Na level in the solution. Na level is more difficult

**8.** In this study, it was observed that some micronutrient items such as Mn were at lower levels. If the tank change intervals are to be increased, the daily additions should be selected from the most commonly used micronutrients. At regular tank change intervals, higher

Potassium, which is present as a free ion in almost all nutrient solutions, has **a pH value** of 2–9 [8]. Like potassium, calcium and magnesium also have a wide pH range. However, the presence of calcium and magnesium is limited due to the presence of other ions. Therefore, if the

Growth, development, and production of plants are based on the **total ionic concentration** of the nutrient solution [10]. The ions of the dissolved salts in the nutrient solution have a colligative ability for nutrient solutions. This property is caused by a force called **osmotic pressure (OP)**. **The osmotic pressure** depends on the amount of dissolved substances [11]. In addition, **the dissolution potential** or **osmotic potential** terms are commonly used in nutrient solutions. Within the nutrient solution, dissolved substances have significant effects on water potential. Solvents reduce the free energy of the water by diluting the water [12]. The salt concentration determines the total amount of salts in a solution. **Electrical conductivity (EC)** is an index of salt concentration. Thus, the osmotic pressure of the nutrient solution is indirectly determined by the **electrical conductivity (EC)** parameter. EC of the nutrient solu-

tion is therefore a good indicator of the amount of ions in the root zone of plants [13].

**Electrical conductivity** or **osmotic pressure** is the first investigated parameter for the concentration of nutrient solution. **The regulation of pH** and **the root temperature** are also other important factors investigated for yield and quality [14]. Nutrients and water absorbers from the nutrient solution continually reinforce their electrical conductivity (EC). Thus, while the concentrations of some ions are reduced, the concentrations of some ions are also increased. This situation occurs both in closed and open hydroponic systems at the same time. For

, the N level is increased by the addition of the nitric acid solution.

−4, Ca2+, and Mg2+ precipitate

**Table 3.** Examination of tank change situation in normal and low calcium nutrient formulation.


**Table 4.** Nutrient solutions for which there is no effect of tank replacement for normal and low calcium nutrient formulation.

In order to evaluate the data obtained for both the plant and the solution, the following results were noted:

**1.** No significant difference was observed between the final fresh weight yields in the four treatments.


Potassium, which is present as a free ion in almost all nutrient solutions, has **a pH value** of 2–9 [8]. Like potassium, calcium and magnesium also have a wide pH range. However, the presence of calcium and magnesium is limited due to the presence of other ions. Therefore, if the nutrient solution contains substances above pH 7; Fe2+, Mn2+, PO<sup>3</sup> −4, Ca2+, and Mg2+ precipitate to the salts. This means that the nutrients received by plants are restricted [9].

Growth, development, and production of plants are based on the **total ionic concentration** of the nutrient solution [10]. The ions of the dissolved salts in the nutrient solution have a colligative ability for nutrient solutions. This property is caused by a force called **osmotic pressure (OP)**. **The osmotic pressure** depends on the amount of dissolved substances [11]. In addition, **the dissolution potential** or **osmotic potential** terms are commonly used in nutrient solutions. Within the nutrient solution, dissolved substances have significant effects on water potential. Solvents reduce the free energy of the water by diluting the water [12]. The salt concentration determines the total amount of salts in a solution. **Electrical conductivity (EC)** is an index of salt concentration. Thus, the osmotic pressure of the nutrient solution is indirectly determined by the **electrical conductivity (EC)** parameter. EC of the nutrient solution is therefore a good indicator of the amount of ions in the root zone of plants [13].

**Electrical conductivity** or **osmotic pressure** is the first investigated parameter for the concentration of nutrient solution. **The regulation of pH** and **the root temperature** are also other important factors investigated for yield and quality [14]. Nutrients and water absorbers from the nutrient solution continually reinforce their electrical conductivity (EC). Thus, while the concentrations of some ions are reduced, the concentrations of some ions are also increased. This situation occurs both in closed and open hydroponic systems at the same time. For

In order to evaluate the data obtained for both the plant and the solution, the following results

**Table 4.** Nutrient solutions for which there is no effect of tank replacement for normal and low calcium nutrient

**Nutrient/ion Normal change (1) Low calcium change (2) Normal no change (3) Low calcium no change (4)**

**(3)**

**At tank change low calcium** 

**(4)**

Nitrogen 61 38 41 48 Phosphorus 26 33 75 81 Potassium 68 116 244 285 Calcium 172 118 95 70 Magnesium 44 52 25 29 Sulfur 197 206 168 167 Sodium 112 115 114 111 Chloride 25 24 28 26 Boron 0.11 0.13 0.09 0.10 Manganese <0.01 <0.01 <0.01 <0.01 Copper 0.09 0.11 0.06 0.07 Zinc 0.05 0.06 0.02 0.03

**Table 3.** Examination of tank change situation in normal and low calcium nutrient formulation.

**Nutrient/ion Initial normal (1) Initial low calcium (2) At tank change normal** 

Nitrogen 119 127 129 129 Phosphorus 28 31 26 31 Potassium 200 233 188 231 Calcium 110 78 116 86 Magnesium 30 33 32 36 Sulfur 97 93 111 111 Sodium 72 72 86 86 Chloride 24 24 28 27 Boron 0.1 0.11 0.12 0.12 Manganese 0.04 0.07 0.04 0.05 Copper 0.08 0.08 0.07 0.08 Zinc 0.06 0.07 0.06 0.08

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

**1.** No significant difference was observed between the final fresh weight yields in the four

were noted:

formulation.

treatments.

example, in a closed hydroponic system with rose production, the nutrient solution in the tank was controlled, and the results showed that the Fe concentration dropped very rapidly, while Ca2+, Mg2+, and Cl<sup>−</sup> increased. In addition, there is no critical condition in the concentration levels of K+ , Ca2+, and SO<sup>4</sup> 2− [15]. The reuse of nutrient solutions requires regulation of EC. The reuse of nutrient solutions has been shown in various studies that have presented positive results for sustainable agricultural production systems [16]. In one of these studies, Brun et al. [17] reduced the EC by adding a water complex to the drainage; has reached the desired EC using recycling systems containing a complementary nutrient solution.

deficiencies, and reduced yield and quality in the plant. It was investigated by Grattan and Grieve that NaCl salinity on the tissue may have a repressive effect on the concentrations of

Potassium Nutrition in Plants and Its Interactions with Other Nutrients in Hydroponic Culture

http://dx.doi.org/10.5772/intechopen.71951

19

Potassium is of vital importance for plants nutrition. In hydroponic systems, the presence of potassium in nutrient solutions affects the processes such as growth, development, and conservation of plants in a positive way. Potassium cation has many tasks in many processes compared to other nutrients. These processes affecting the development of plants can be listed as **the cation exchange capacity (CEC)**, **the pH value**, **electrical conductivity (EC)**, **the root temperature**, **total ionic concentration**, **the dissolution potential (osmotic potential)**, **the ionic mutual ratio**, **the mutual ratio of anions**, **the mutual ratio of cations**, **oxygen content**, and **CO2**

1 Department of Physics, Faculty of Arts and Science, Pamukkale University, Kinikli,

[1] Salisbury FB, Ross CW. Plant Physiology. California, USA: Wadsworth Publishing

[2] Marschner H. Mineral Nutrition of Higher Plants. 2nd ed. London: Academic Press;

[3] Usherwood NR. The role of potassium in crop quality. In: Munson RS, editor. Potassium

[4] Ganeshamurthy AN, Satisha GC, Patil P. Potassium nutrition on yield and quality of fruit crops with special emphasis on banana and grapes. Karnataka The Journal of

[5] Mitra SK, Dhaliwal SS. Effect of potassium on fruit quality and their storage life.

2 Department of Chemistry, Faculty of Science, Gazi University, Ankara, Turkey

in Agriculture. Madison, WI: ASA-CSSASSSA; 1985. pp. 489-513

Proceedings IPI-OUAT-IPNI International Symposium; 2009

micronutrites and macronutrients (N, P, K, Ca, Mg, and S) [26].

\* and Ali Cengiz Çalişkan<sup>2</sup>

\*Address all correspondence to: bcaliska@gmail.com

Company; 1992. ISBN:0-534-15162-0

Agricultural Science. 2011;**24**(1):29-38

1995. ISBN: 9780124735439

**3. Conclusion**

**concentration.**

**Author details**

Betül Çalişkan<sup>1</sup>

Denizli, Turkey

**References**

The ions which are active on EC are Ca2+, Mg2+, K+ , Na+ , H<sup>+</sup> , NO3−, SO<sup>4</sup> 2−, Cl<sup>−</sup> , HCO3−, and OH− ions [18]. Micronutrients such as Fe, Cu, Zn, Mn, B, Mo, and Ni do not have a significant effect on EC, since they are less likely to be taken up by plants than macronutrients [19].

The nutrient solutions contain essentially six nutrients together with Ca, Mg, and S, with preference for K, N, and P. **The ionic mutual ratio** was developed by Steiner (1961). This concept is based on **the mutual ratio of anions** such as NO<sup>3</sup> − , H<sup>2</sup> PO<sup>4</sup> − , and SO<sup>4</sup> 2− and **the mutual ratio of cations** such as K+ , Ca2+, and Mg2+. Such a ratio affects not only the total amount of each ion in solution but also the quantitative relationship that holds the ions together [10].

Soilless cultivation provides various viable and controllable possibilities to increase quality of crops and production. Parameters such as **temperature**, **pH**, **electrical conductivity**, and **oxygen content** in the nutrient solution are traceable. It is essential that these parameters are checked in a timely and accurate manner so that the advantage does not become a disadvantage [15].

When the temperature of the nutrient solution increases, **the consumption of O2** increases. If ventilation in the root is not sufficient, **the concentration of CO2** in the root increases [20]. In some vegetables, various investigations have been carried out on the reduction of **CO2 concentration** by using potassium peroxide, which acts as an oxygen source [21].

Potassium is the most desirable cationic minerals for plants and constitutes 10% of the plant dry matter. Due to the reductions in KNO<sup>3</sup> fertilizers in the nutrient solution, the dry matter content of leaves, crowns, and roots decreased significantly. This slowed down growth and reduced the number of leaves [22]. There are a number of investigations reporting that the stomatal conductance is decreasing due to the lack of K. Accordingly, it has been reported that CO<sup>2</sup> fixation and phloem export are also decreasing [23]. In addition, in maize and wheat production, insufficient K levels have been observed to increase the yield of these products [24].

Various effects of K nutrition should be considered taking into account the total ion concentration (EC). At K nutrition, the relationship of K to other cations should be investigated. Among these cations, Ca, Mg, and Na in the saline irrigation water are primarily present. As a result of increasing K/Ca ratio, the storage quality is improved. In addition, flavor factors such as sugar and acid content have been increased [25].

Poor water quality can lead to excessive concentrations of NaCl in the nutrient solution. Therefore, the nutrient-ion activities may decrease and the ratios of Na+ :Ca2+, Na+ :K+ , Ca2+:Mg2+, and Cl<sup>−</sup> :NO3− may increase [26]. This can lead to osmotic and specific-ion damage, nutritional deficiencies, and reduced yield and quality in the plant. It was investigated by Grattan and Grieve that NaCl salinity on the tissue may have a repressive effect on the concentrations of micronutrites and macronutrients (N, P, K, Ca, Mg, and S) [26].

### **3. Conclusion**

example, in a closed hydroponic system with rose production, the nutrient solution in the tank was controlled, and the results showed that the Fe concentration dropped very rapidly,

EC. The reuse of nutrient solutions has been shown in various studies that have presented positive results for sustainable agricultural production systems [16]. In one of these studies, Brun et al. [17] reduced the EC by adding a water complex to the drainage; has reached the

ions [18]. Micronutrients such as Fe, Cu, Zn, Mn, B, Mo, and Ni do not have a significant effect

The nutrient solutions contain essentially six nutrients together with Ca, Mg, and S, with preference for K, N, and P. **The ionic mutual ratio** was developed by Steiner (1961). This concept

Soilless cultivation provides various viable and controllable possibilities to increase quality of crops and production. Parameters such as **temperature**, **pH**, **electrical conductivity**, and **oxygen content** in the nutrient solution are traceable. It is essential that these parameters are checked in a timely and accurate manner so that the advantage does not become a disadvan-

some vegetables, various investigations have been carried out on the reduction of **CO2 con-**

Potassium is the most desirable cationic minerals for plants and constitutes 10% of the plant

content of leaves, crowns, and roots decreased significantly. This slowed down growth and reduced the number of leaves [22]. There are a number of investigations reporting that the stomatal conductance is decreasing due to the lack of K. Accordingly, it has been reported that

 fixation and phloem export are also decreasing [23]. In addition, in maize and wheat production, insufficient K levels have been observed to increase the yield of these products [24].

Various effects of K nutrition should be considered taking into account the total ion concentration (EC). At K nutrition, the relationship of K to other cations should be investigated. Among these cations, Ca, Mg, and Na in the saline irrigation water are primarily present. As a result of increasing K/Ca ratio, the storage quality is improved. In addition, flavor factors such as

Poor water quality can lead to excessive concentrations of NaCl in the nutrient solution.

may increase [26]. This can lead to osmotic and specific-ion damage, nutritional

, Na+ , H<sup>+</sup>

> − , H<sup>2</sup> PO<sup>4</sup> −

, Ca2+, and Mg2+. Such a ratio affects not only the total amount of each ion

desired EC using recycling systems containing a complementary nutrient solution.

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

on EC, since they are less likely to be taken up by plants than macronutrients [19].

in solution but also the quantitative relationship that holds the ions together [10].

When the temperature of the nutrient solution increases, **the consumption of O2**

**centration** by using potassium peroxide, which acts as an oxygen source [21].

ventilation in the root is not sufficient, **the concentration of CO2**

increased. In addition, there is no critical condition in the concentra-

2− [15]. The reuse of nutrient solutions requires regulation of

, NO3−, SO<sup>4</sup>

, and SO<sup>4</sup>

fertilizers in the nutrient solution, the dry matter

:Ca2+, Na+

:K+

, Ca2+:Mg2+,

2−, Cl<sup>−</sup>

, HCO3−, and OH−

2− and **the mutual ratio** 

increases. If

in the root increases [20]. In

while Ca2+, Mg2+, and Cl<sup>−</sup>

, Ca2+, and SO<sup>4</sup>

The ions which are active on EC are Ca2+, Mg2+, K+

is based on **the mutual ratio of anions** such as NO<sup>3</sup>

dry matter. Due to the reductions in KNO<sup>3</sup>

sugar and acid content have been increased [25].

Therefore, the nutrient-ion activities may decrease and the ratios of Na+

tion levels of K+

**of cations** such as K+

tage [15].

CO<sup>2</sup>

and Cl<sup>−</sup>

:NO3−

Potassium is of vital importance for plants nutrition. In hydroponic systems, the presence of potassium in nutrient solutions affects the processes such as growth, development, and conservation of plants in a positive way. Potassium cation has many tasks in many processes compared to other nutrients. These processes affecting the development of plants can be listed as **the cation exchange capacity (CEC)**, **the pH value**, **electrical conductivity (EC)**, **the root temperature**, **total ionic concentration**, **the dissolution potential (osmotic potential)**, **the ionic mutual ratio**, **the mutual ratio of anions**, **the mutual ratio of cations**, **oxygen content**, and **CO2 concentration.**
