3. Hydroponic cultivation system: NFT

hydroponics is the technique of growing plants without soil, where the roots develop in balanced nutrient solution, with all the nutrients essential to the development of the plant, being a technique of cultivation in economically protected environments feasible and environmentally

For the success of the hydroponic cultivation, it is necessary to develop adequate computational tools that will assist the producer in the calculation of the correct dosages of the solutions, since there are many crops to be considered, as well as a large amount of inputs for fertilization.

A computerized system to calculate the hydroponic solution allows to offer more accurate and fast results. Using software, the grower who grows in a hydroponic system will have a better facility to calculate the correct dosage of nutrients, obtaining more satisfactory results with a lower cost. In this context, accessing tools via the Internet makes it easier to use programs, regardless of geographical location, and there is no need to install programs on personal

In this sense, the objective of the research was the development of a free software for use over the Internet, with a friendly interface and intuitive navigation, for calculation of nutrient

According to Embrapa [1], protected cultivation allows farmers to offer the market products with good visual quality in periods of low supply and high prices, contributing to a good profitability, which justifies the investment with the protected structures. Brazil has more than 30,000 hectares of protected cultivation, being the country with the largest cultivated area in this

Protected cultivation, which has the potential to double the productivity reached in the open field, emerges as a technique capable of reconciling high yields with quality in environmental conditions that are potentially stressful to plants and may compromise the production of vegetables. In the last two decades, the protected crop, worldwide, increased 400%, from 700,000 to 3.7 million hectares. The use of hydroponics in protected crops has been used as a tool to solve a wide range of problems, including the reduction of soil and groundwater contamination, and the

Among the several hydroponic systems that do not use substrates, "Nutrient Film Technique-NFT" is the most widespread in Brazil and in the world [3]. This technique favors the continuous or intermittent circulation of the nutrient solution in culture channels, which can be varied in size and made by different materials, being the most common PVC, polyethylene, polypropylene and masonry [4]. In this agricultural production system, there is still a need for the development of new technologies, notably the need for new software to assist the producer in calculating the nutrient solution [5], since the correct calculation of the nutrient solution is fundamental for success in production. The supply of nutrients at levels suitable for growth, minimizing production losses and providing better quality to fruit vegetables [6]. With the use and advancement of information technologies in the development of software for the Internet,

solution for fruit vegetables and leaves in hydroponic NFT system.

2. Hydroponic system cultivation

nutritional biofortification of olive trees [2].

system, in South America.

sound. Proper plant nutrition also increases crop tolerance to pest and disease attack.

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

computers.

In Brazil, the hydroponic crop is predominantly made by the NFT system. Many of these hydroponic crops are not successful, mainly due to the lack of knowledge of the formulation and the adequate management of nutrient solutions [12].

In the NFT system, the plants grow having their root system in a channel through which the nutrient solution circulates. The pioneer of this technique was Allen Cooper, at the Glasshouse Crop Research Institute, Littlehampton, England, in 1965, who determined that the thickness of the flow of the nutrient solution passing through the roots of the plants should be small (laminar) in such a way that the roots are not completely submerged, lacking the necessary oxygen [13]. In this system, there is no need to place any material inside the channels, such as stones, sand, expanded clay and burnt rice straw, and the canals contain only the roots of the plants and the nutrient solution. The nutrient solution is stored in a reservoir, from where it is repressed to the top of the cultivation bed (bench), passing through the channels, being collected at the bottom of the bed, to return to the tank [14].

#### 3.1. Mineral nutrition of plants

One of the basic principles for plant production, in both soil and nonsoil cultivation systems, (hydroponics) is to provide all the nutrients the plant needs. If there is a nutrient imbalance in the environment in which the plant grows, the production will be reduced, hence the need to supply all the elements that the plants need, in the correct dose, according to the requirements of each crop [15].

Several chemical elements are essential for the development of plants, which are presented in Table 1.

These elements can be classified according to their origin in:


The division between macronutrients and micronutrients takes into account only the amount that the plant absorbs from each nutrient to complete its productive cycle. The plants have about 90– 95% of their weight in C, H, O, which are elements that come from air and water, and are abundant in nature. Therefore, in the nutrient solution, the emphasis is on the mineral elements [10].

3.2. Water as an essential element in hydroponics

3.3. Suggestions for nutritional solutions

hydroponics.

In soilless cultivation, water quality is essential, as it will dissolve the essential elements that will nourish the plants. The water used must be potable and may be from artesian wells, water courses or rainfall collection [13]. In hydroponics, all nutrients are supplied to the plants in the solution that is prepared with different fertilizers. There are several salts that provide the same nutrients for plants; one should opt for those that are easier to dissolve in water, inexpensive and easily found in the trade. Table 2 presents some of the most used fertilizers in

Software for Calculation of Nutrient Solution for Fruits and Leafy Vegetables in NFT Hydroponic System

Tables 3–6 present nutritional solutions for the cultivation of tomato, cucumber and lettuce. The difference between solution A and solution B is in the amount of calcium nitrate used. Solution A is used in the growing phase of the plant and solution B is used in the fruiting phase. For the formation of the fruits, there is a greater absorption of calcium and nitrogen by

g 1000 L

Solution A Solution B Solution A Solution B

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the plants, a greater quantity of these nutrients being necessary in that phase.

Table 3. Composition of nutritive solutions for tomato and cucumber [13].

Table 4. Preparation of solution containing micronutrients [13].

Fertilizers Molecular formula Nutrients Tomato Cucumber

Potassium nitrate KNO3 N. K 200 200 200 200 Magnesium sulfate MgSO4 Mg, S 500 500 500 500 Potassium phosphate KH2PO4 K, P 270 270 270 270 Potassium sulfate K2SO4 K, S 100 100 — — Calcium nitrate Ca(NO3)2 N, Ca 500 680 680 1.357 Iron Fe (chelated) Fe 25 25 25 25 Micronutrients Micronutrients — 150 mL 150 mL 150 mL 150 mL

Fertilizers Molecular formula Nutrients g 1000 L Boric acid H3BO3 B 7.50 Magnesium sulfate MnCl2 4H2O Mn 6.75 Cupric chloride CuCl2+2H2O Cu 0.37 Ammonium molybdate (NH4)6 MO7O24 4H2O Mo 0.15 Zinc sulfate heptahydrate ZnSO4 7H2O Zn 1.18


Table 1. Chemical elements used in the production of plants.


Table 2. Composition of some fertilizers used in hydroponics (macronutrients) [14].

#### 3.2. Water as an essential element in hydroponics

These elements can be classified according to their origin in:

The division between macronutrients and micronutrients takes into account only the amount that the plant absorbs from each nutrient to complete its productive cycle. The plants have about 90– 95% of their weight in C, H, O, which are elements that come from air and water, and are abundant

in nature. Therefore, in the nutrient solution, the emphasis is on the mineral elements [10].

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

Carbon C Magnesium Mg Hydrogen H Manganese Mn Oxygen O Iron Fe Nitrogen N Zinc Zn Phosphor P Boron B Potassium K Copper Cu Sulfur S Molybdenum Mo Calcium Ca Chlorine Cl

Fertilizers Molecular formula N P K Ca Mg S

Potassium nitrate KNO3 14 — 36.5 —— — Sodium and potassium nitrate NaNO3 13 — 11.6 —— — Ammonium nitrate NH4NO3 34 — — —— — Calcium nitrate Ca(NO3)2 15 — — 20 — — Nitrocalcium NH4NO3 + limestone 22 — — 7 — — Monoammonium phosphate NH₄H₂PO₄ 10 21.1 — —— — Diammonium phosphate (NH4)2HPO4 18 20.2 — —— — Urea (NH2)2CO 45 — — —— — Ammonium sulfate (NH4)2SO4 20 — — —— 24 Potassium phosphate KH2PO4 — 24 31 —— — Potassium chloride KCl — — 49.8 —— — Potassium sulfate K2SO4 — — 41.5 — — 17 Magnesium sulfate MgSO4 —— — — 9.5 13

%

• Nonmineral macronutrients: C, H, O;

• Mineral macronutrients: N, P, K, Ca, Mg, S; • Micronutrients: Mn, Fe, B, Zn, Cu, Mo, Cl.

Table 1. Chemical elements used in the production of plants.

Table 2. Composition of some fertilizers used in hydroponics (macronutrients) [14].

In soilless cultivation, water quality is essential, as it will dissolve the essential elements that will nourish the plants. The water used must be potable and may be from artesian wells, water courses or rainfall collection [13]. In hydroponics, all nutrients are supplied to the plants in the solution that is prepared with different fertilizers. There are several salts that provide the same nutrients for plants; one should opt for those that are easier to dissolve in water, inexpensive and easily found in the trade. Table 2 presents some of the most used fertilizers in hydroponics.

#### 3.3. Suggestions for nutritional solutions

Tables 3–6 present nutritional solutions for the cultivation of tomato, cucumber and lettuce. The difference between solution A and solution B is in the amount of calcium nitrate used. Solution A is used in the growing phase of the plant and solution B is used in the fruiting phase. For the formation of the fruits, there is a greater absorption of calcium and nitrogen by the plants, a greater quantity of these nutrients being necessary in that phase.


Table 3. Composition of nutritive solutions for tomato and cucumber [13].


Table 4. Preparation of solution containing micronutrients [13].


Table 5. Nutrient solution composition for lettuce cultivation [10].

These quantities are used to prepare 450 mL stock solution. Hot water should be used to dissolve fertilizers well. Use 150 mL of the micronutrient-containing solution per 1000 L of culture solution.

sulfate and 60 g of disodium EDTA. After dissolution, add EDTA to the ferrous sulfate solution. Make the air bubble in the solution obtained until complete dissolution of any precipitate formed. Store in a dark bottle and protect from light. If the producer prefers, he may purchase commercial products to be used as a nutrient solution for hydroponic cultivation, intended for various leafy

Lettuce 238 62 426 161 24 32 0.3 0.05 5 0.4 0.05 0.3 Tomato 169 62 311 153 43 50 0.2 0.03 4.3 1.1 0.05 0.3 Chili 152 39 245 110 29 32 0.3 0.03 3.7 0.4 0.05 0.3 Eggplant 179 46 303 127 39 48 0.3 0.05 3.2 0.6 0.05 0.3 Cucumber 174 56 258 153 41 54 0.2 0.03 4.3 1.1 0.05 0.3 Melon 170 39 225 153 24 32 0.2 0.03 2.2 0.6 0.05 0.3 Strawberry 125 46 176 119 24 32 0.2 0.03 2.5 0.4 0.05 0.3

<sup>3</sup> P K Ca Mg S B Cu Fe Mn Mo Zn

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Software for Calculation of Nutrient Solution for Fruits and Leafy Vegetables in NFT Hydroponic System

Table 7 presents suggestions for the preparation of nutrient solutions in the NFT system for

The calculation of the nutrient solution is done in a simplified way, dividing the fertilizers by

F1 <sup>¼</sup> <sup>100</sup> � nutrient

For each 100g of the fertilizer chosen, it is multiplied by the recommended amount of nutrient in the solution, which in this first stage can be calcium (Ca) or potassium (K), and then divided by the concentration of Ca or K in the fertilizer, thus obtaining the amount of

Generally, the fertilizer used contains other nutrients necessary for the crop, making it neces-

The value of F1 is the amount obtained in formula (1), which stipulates the amount of fertilizer to supply Ca or K, multiplied by the concentration (%) of the other nutrient in the fertilizer,

sary the calculation for its use, using the following formula for the calculation.

) in its formulation,

concentration ð Þ % (1)

vegetables and already used by many producers on a commercial scale.

different types of hardwood vegetables.

Table 7. Values for nutrient solutions by the NFT system [16].

4. Calculation of nutrient solution

divided by 100, which corresponds to 100 g.

fertilizer chosen.

Culture N-NO�

(mg L�<sup>1</sup> )

In their preparation, the amounts of fertilizers are used, as shown in Table 6.

nutrients, taking as starting point the fertilizers containing nitrate (NO�<sup>3</sup>

such as calcium nitrate and potassium nitrate, if the formula:

In order to be efficiently absorbed by the roots, the iron must be chelated, so a solution containing 10 mg/mL of Fe must be prepared, to dissolve separately in each 450 mL of water, 50 g of ferrous


Table 6. Quantities of salts for the preparation of nutrient solution [10].

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Table 7. Values for nutrient solutions by the NFT system [16].

sulfate and 60 g of disodium EDTA. After dissolution, add EDTA to the ferrous sulfate solution. Make the air bubble in the solution obtained until complete dissolution of any precipitate formed. Store in a dark bottle and protect from light. If the producer prefers, he may purchase commercial products to be used as a nutrient solution for hydroponic cultivation, intended for various leafy vegetables and already used by many producers on a commercial scale.

In their preparation, the amounts of fertilizers are used, as shown in Table 6.

Table 7 presents suggestions for the preparation of nutrient solutions in the NFT system for different types of hardwood vegetables.

#### 4. Calculation of nutrient solution

These quantities are used to prepare 450 mL stock solution. Hot water should be used to dissolve fertilizers well. Use 150 mL of the micronutrient-containing solution per 1000 L of

Fertilizer Formula molecular g / 1000 L Calcium nitrate Ca(NO3)2 1000 Potassium nitrate KNO3 600 Potassium chloride KCl 150 Monoammonium phosphate NH₄H₂PO₄ 150 Magnesium sulfate MgSO4 250 Micronutrient solution — 500 mL Fe-EDTA solution — 500 mL Chlorine Cl 100 Boric acid H3BO3 20 Iron Fe (chelated) 100 Magnesium sulfate MnCl2 4H2O 50 Zinc sulfate heptahydrate ZnSO4 7H2O 20 Cupric chloride CuCl2+2H2O 6 Ammonium molybdate (NH4)6 MO7O24 4H2O 0.1

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

In order to be efficiently absorbed by the roots, the iron must be chelated, so a solution containing 10 mg/mL of Fe must be prepared, to dissolve separately in each 450 mL of water, 50 g of ferrous

Product (g/1000 L)

Calcium nitrate Ca(NO3)2 750 Potassium nitrate KNO3 500 Phosphate monoammonium NH₄H₂PO₄ 150 Magnesium sulfate MgSO4 400 Copper sulfate CuCl2+2H2O 0.15 Zinc sulfate ZnSO4 7H2O 0.5 Manganese sulfate MnCl2 4H2O 1.5 Boric acid H3BO3 2.3 Ammonium molybdate (NH4)6 MO7O24 4 H2O 0.15 Tenso-Fe® FeEDDHMA-6% Fe 30 Dissolvine® FeEDTA-13% Fe 13.8 Ferrilene® FeEDDHa-6% Fe 30 FeEDTANa2 (10 mg mL Fe) FeEDTANa2 180 mL

culture solution.

Table 5. Nutrient solution composition for lettuce cultivation [10].

Table 6. Quantities of salts for the preparation of nutrient solution [10].

The calculation of the nutrient solution is done in a simplified way, dividing the fertilizers by nutrients, taking as starting point the fertilizers containing nitrate (NO�<sup>3</sup> ) in its formulation, such as calcium nitrate and potassium nitrate, if the formula:

$$\text{F1} = \frac{100 \times \text{nTprint}}{\text{concentration}} (\%) \tag{1}$$

For each 100g of the fertilizer chosen, it is multiplied by the recommended amount of nutrient in the solution, which in this first stage can be calcium (Ca) or potassium (K), and then divided by the concentration of Ca or K in the fertilizer, thus obtaining the amount of fertilizer chosen.

Generally, the fertilizer used contains other nutrients necessary for the crop, making it necessary the calculation for its use, using the following formula for the calculation.

The value of F1 is the amount obtained in formula (1), which stipulates the amount of fertilizer to supply Ca or K, multiplied by the concentration (%) of the other nutrient in the fertilizer, divided by 100, which corresponds to 100 g.

Once the result of F2 is obtained, if this result is lower than the recommended amount for the crop, the process will be redone, starting with F1, using another fertilizer.

PHP has source code available for everyone at no cost. The license to use and edit is Open Source, meaning no one can market any modified version of PHP, and any modification must continue with Open Source code for users to explore and modify. This license system does not bring profit to developers because they make everything available to the public for free, and the public, in turn, helps by reporting bugs and helping to modify the source code. Many companies support PHP developers because they do not aim for profit by creating and developing the program. PHP is heavily used with Linux and MySQL, two other Open Source programs [18]. Other advantages of the system are: to be totally free, to work on any operating system in which it is possible to install a web server (multi-platform) and to be able to be easily connected with

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Due to its great autonomy, it is a language that allows to create dynamic web sites, allowing a user interaction through forms, URL parameters and links. The difference of PHP with respect to languages similar to Javascript is that the PHP code can be executed on the server, being sent to the client only pure html. In this way, it is possible to interact with existing databases and applications on the server, with the advantage of not exposing the source code to the client. This can be useful when the program is dealing with passwords or any kind of confidential information.

MySQL is a relational database management system. A relational database stores data in separate tables instead of putting all the data in one place. This provides speed and flexibility [20]. SQL is the most common default language used for database access and is defined by the ANSI/ ISO SQL standard. The SQL standard has been evolving since 1986, and there are several

The MySQL is an Open Source software. Open Source means that it is possible for anyone to use and modify the program. Anyone can download MySQL over the Internet and use it

The MySQL database server is extremely fast, reliable, and easy to use. The MySQL Server also

The MySQL Server was originally developed to handle very large databases much faster than existing solutions and has been used successfully in high demand production environments

The MySQL Database Program is a client/server system consisting of a multitasking SQL server that supports different accesses, various client programs and libraries, administrative

Cascading Style Sheets, or Cascade Style Sheets, are formatting files for HTML documents. Its great advantage is in the association with HTML pages, which greatly facilitates the process of formatting serial pages. For example, suppose there is a site consisting of dozens of pages, and

has a set of very practical features developed with the cooperation of users [21].

OpenData Base Connectivity (ODBC) standard systems [19].

5.2. The MySQL relational database system

tools and various programming interfaces [21].

5.3. The cascading style sheets: CSS3

versions [21].

without paying for it [22].

for several years [20].

In a second step, the fertilizers containing potassium (K) are used, such as potassium phosphate monobasic, potassium chloride (white) or potassium sulfate. After choosing the fertilizer, it must be checked if there is potassium leftover from the first calculation, and if this happens, the following formula should be used:

If there is no "leftover," this formula is used in the same way as previously used, based on the fertilizer chosen.

This is done until all the macronutrients are calculated by calculating the recommended amounts for each crop.

In a final step of the calculation, not visible to the user, the calculations are made using the micronutrient contents of the fertilizers: boric acid, copper sulfate, manganese sulfate, zinc sulfate, sodium molybdate and ferrous sulfate. To calculate the macronutrients, the formula (1) is used.

Finally, the results are converted to the capacity of the chosen tank, and for 1000 L, the results are multiplied by 1, if they are 2000 L, the results are multiplied by 2, so successively up to the maximum value of 5000 L.

Next, a report is presented, which can be converted to PDF format for print, and the PHP library, mPDF that converts HTML to PDF, was used for this task. The report contains:

Fertilizers: option where all the fertilizers used to calculate nutrient solutions are visualized.

In the "Help" section, you can find the following options: Tutorial, where you can access a tutorial explaining the steps to create a solution and calculate it and get information to contact the system developers, as well as the tools used.

In the current version of the system, there is an administrative area, where it is possible to measure the number of users registered, where the "Administrators" group that associates with the user was added, restricting access to this area only to users belonging to this group. With the option "User Report," the name of the users with a totalizer is listed, leaving the structure open for more options for this area.
