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Abu Dhabi Farmers’ Services Centre Technical Development Section Protected Agriculture Unit Hydroponics manual Contents 1. Introduction

1.1. Purpose and objectives of the manual 1.2. What is hydroponics 1.3. The potential and limitations of hydroponics 1.4. Nutrients and other plant growth requirements

2. The hydroponics system

2.1. Components of the hydroponics system 2.2. Water supply 2.3. Fertigation system 2.4. Delivering the nutrient solution to the crops 2.5. Plant growth systems 2.6. Types of media for substrate hydroponics 2.7. Types of substrate hydroponics systems 2.8. Greenhouse facilities and climate control systems

3. Management of the hydroponics system

3.1. Choosing the correct substrate 3.2. Hydroponics chemistry and using the fertigation system 3.3. Electrical conductivity and pH control 3.4. Hydroponics nutrition and crop nutrient calculations 3.5. Diagnosing nutritional deficiencies 3.6. Sampling nutrient solutions 3.7. Calibrating pH meters 3.8. Calibrating EC meters 3.9. Measuring distribution uniformity of irrigation 3.10. Measuring run off volume of irrigation 3.11. Hydroponics system hygiene 3.12. Checklist for adopting good agricultural practices in hydroponics

4. Appendices

4.1. Greenhouse structures and specifications 4.2. Greenhouse covers 4.3. Hydroponic system specifications

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Photographs [To incorporate into the document during publication]

No. Section Description Got To get Ready

Front cover and introduction:

1 1 8 general pictures of hydroponics production

2 1 showing overall system, crops at different stages

3 1 within the system, final products

4 1

5 1

6 1

7 1

8 1

Main components of hydroponics system:

9 2.1 Water supply, desalination unit

10 2.1 Fertigation system

11 2.1 Substrate

12 2.1 Greenhouse facilities

13 2.1 Climate control system

14 2.1 Power supply

Details of fertigation system:

15 2.3 Fresh water storage tanks

16 2.3 Nutrient and chemical storage tanks

17 2.3 Mixing tank

18 2.3 pH meter

19 2.3 EC meter

20 2.3 Control system

21 2.3 Irrigation system

22 2.3 Pumps

23 2.3 Waste water collection and recycling system

24 2.3 Fresh water storage tanks

25 2.3 Nutrient and chemical storage tanks

Different injection systems:

26 2.4 Suction injection

27 2.4 Pressure differential injection

28 2.4 Pump injection

Different production systems:

29 2.5 Water culture – 2 photos showing the most relevant systems

30 2.5

31 2.6 Substrate culture – 4 photos showing the most relevant

32 2.6 systems

33 2.6

34 2.6

Common fertilisers used:

35 3.2 Tank A – 4 photos showing the most common fertilisers

36 3.2 (container and/or bag and/or material)

37 3.2

38 3.2

39 3.2 Tank B – 4 photos showing the most common fertilisers

40 3.2 (container and/or bag and/or material)

41 3.2

42 3.2

Common acids and bases used:

43 3.3 Acid – container and/or bag and/or material of most common used

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44 3.3 Base – container and/or bag and/or material of most common used

Common nutrient deficiencies:

45 3.5 6 pictures showing the most common nutrient deficiencies

46 3.5

47 3.5

48 3.5

49 3.5

50 3.5

Other information:

51 3.6 Sampling nutrient solutions

52 3.7 Calibrating pH meters

53 3.8 Calibrating EC meters

54 3.9 Measuring distribution uniformity

55 3.10 Measuring run off volume

56 3.11 Hydroponics system hygiene – 4 pictures showing the most

57 3.11 Important steps to take

58 3.11

59 3.11

Greenhouse structures:

60 4.1 Main components of greenhouse structure – 4 pictures

61 4.1 showing the most important parts

62 4.1

63 4.1

64 4.1.3 Greenhouse cooling systems – 2 pictures

65 4.1.3

66 4.2 Greenhouse shading – 4 pictures of main covers and

67 4.2 shading options

68 4.2

69 4.2

Back cover – harvesting, final products, success stories

70 Harvesting of high value vegetables from hydroponics

71 production systems – 4 pictures

72

73 The ADFSC value chain and market – 4 pictures

74

75

76 Picture of successful hydroponics farmers (with text) – from

77 2 demonstration farms in Western Region (Ali & Yafoor)

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1. Introduction 1.1. Purpose and objectives of the manual The purpose of the manual is to provide information about hydroponics to farm owners and farm managers who have recently started, or about to start, hydroponics production in Abu Dhabi Emirate. It is expected that the use of the manual will help to improve the technical and economic sustainably of hydroponic production systems, and help ensure appropriate financial margins and returns from investments in hydroponics. The objectives of the manual are to help farm owners and farm managers to:

1. Understand the key principles and components of hydroponics systems. 2. Understand the different types of hydroponics system and growing media. 3. Understand plant growth requirements and how these relate to hydroponics system. 4. Measure and manage important operational parameters within the hydroponics

system, including EC, pH, distribution uniformity of irrigation, and irrigation run off. 5. Develop knowledge and skills in hydroponics chemistry and fertigation. 6. Develop knowledge and skills in hydroponics nutrition, including crop nutrient

calculations and diagnosing nutritional deficiencies. 7. Understand the different types of greenhouse production facilities, including climate

control systems, and how to manage these for hydroponics production. 8. Appreciate and understand the recommended technical specifications for each

component of the hydroponics system and greenhouse facilities. 9. Build capacity for the day to day management of hydroponics production systems,

including system hygiene, and how to troubleshoot common operational issues. 10. Overall, manage hydroponics production systems according to good agricultural

practices. It is expected that most or all hydroponics production systems in Abu Dhabi Emirate will be growing a range of moderate to high value vegetables for domestic markets. The manual is therefore focused on these production systems, although the technical information provided is also relevant for farmers aiming to grow new products for existing or new markets. The manual is also useful as reference material for a range of value chain stakeholders in United Arab Emirates and beyond, including input suppliers, extension service providers, investment fund managers, and policy makers. The manual is not intended to replace the specific technical information provided by the commercial suppliers of the various components of the hydroponics systems. Nor should it replace the technical support given by these companies, provided through warranties and other arrangements. Furthermore, the manual should not be a substitute for the regular guidance, advice, and training provided by extension specialists from the Abu Dhabi Farmers’ Services Centre. The manual should be used in conjunction with these other sources of operational and technical support. In addition to the manual, a range of crop growing guides are available from the Technical Services Division of Abu Dhabi Farmers’ Services Centre. These guides give detailed information for growing specific vegetables using hydroponic production systems, including for tomatoes and capsicums.

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1.2. What is hydroponics? Hydroponics is the process of growing plants without soil. In hydroponic systems plants are grown in a variety of different media and the essential elements plants need to grow are supplied in the nutrient solution. This allows greater control of nutrient supply and plant growth. Hydroponics also allows the root environment to be modified to improve one or more aspects of plant production. Hydroponics systems are frequently incorporated into greenhouse environments. This further improves plant production by giving increased control over the plants environment and protection from pests, diseases and adverse climatic conditions. Many hydroponics systems also allow runoff water to be recycled, greatly increasing the efficiency of water use. Hydroponics can be used to grow almost any crop. However, it is particularly suitable for growing high value and/or high turnover crops, as the set-up costs are greater than with conventional soil based production. 1.3. The potential and limitations of hydroponics The potential of hydroponic production systems include:

1. Use in places where in-ground, soil based, plant growth is not viable 2. Isolation from diseases and pests found in the soil 3. Direct and immediate control of nutrient content, salinity and acidity, and root zone

environment 4. Higher and more stable yields 5. Intensive planting 6. Greater water and fertiliser use efficiency 7. Ease of disinfecting greenhouses between crops 8. No weeding required 9. No cultivation or preparation of soil before planting 10. Lower operational costs associated with water and nutrient recycling 11. Reduced transplant shock 12. Decreased use of hazardous pesticides 13. More predictable yield and time of harvest 14. Ability, in some systems, to adjust working height from ground level to a better

height for planting, cultivation and harvesting 15. Ability to fully contain run off water

The limitations of hydroponic production systems include:

1. Higher set up cost, relative to conventional production systems 2. Higher level of operational skills, relative to conventional production systems 3. Not economically viable for all crops 4. Increased risk of spread of soil-borne diseases 5. Greater risk that crop will suffer nutrition problems 6. System failure results in rapid plant death

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1.4. Nutrients and other plant growth requirements Plants need nutrients, water, oxygen, carbon dioxide, a suitable root zone environment, physical support, and light to grow and thrive. 1.4.1. Nutrients Nutrients are the chemical elements and compounds that are necessary for plant growth. There are 17 chemical elements that are required for plant growth. Carbon, hydrogen and oxygen come from the atmosphere. The other nutrients come from the soil. In hydroponic systems, these are supplied as readily available water soluble minerals in a balanced nutrient solution, eliminating the need for soil. Nutrients are divided into three groups: macronutrients, micronutrients, and non-essential nutrients. Macronutrients are nutrients required in large amounts for plant growth, including: Carbon (C), Hydrogen (H), Nitrogen (N), Oxygen (O), Phosphorus (P), Potassium (K), Calcium (Ca) Magnesium (Mg) and Sulphur (S). Micronutrients are nutrients required in small amounts for plant growth, including: Iron (Fe), Chlorine (Cl), Boron (B), Manganese (Mn), Copper (Cu), Zinc (Zn), Nickel (Ni) and Molybdenum (Mo). Non-essential nutrients include Sodium, Cobalt, Nickel, and Silicon. 1.4.2. Macronutrients Nitrogen Nitrogen is central to plant growth. It is a major component of amino acids which are the building blocks of all proteins, including enzymes, which control metabolic processes. Nitrogen is present in chlorophyll, the green pigment required for photosynthesis. It is also responsible for the plant’s overall growth, increasing seed and fruit production and leaf quality. A plant can take up nitrogen in two different forms: the preferred form is nitrate (NO3

-), the other is ammonium form (NH4

+). Calcium nitrate and potassium nitrate are major fertilisers used in most hydroponics mixes. Ammonium nitrate and Ammonium sulphate are also used in small amounts to supply the ammonium form of nitrogen. Phosphorus Phosphorus is used in photosynthesis and in the production of flowers and seeds. It also encourages root growth. Plants deficient in phosphorus can develop sparse dark green leaves with brown or purple discoloration of the lower leaf surface. The most common fertilisers used to supply phosphorus in hydroponics mixes are mono-ammonium phosphate and potassium dihydrogen phosphate. Potassium

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Potassium is necessary during all stages of plant development, particularly during fruit development. It is absorbed by plants in larger amounts than any other nutrient with the exception of nitrogen and in some cases calcium. It is involved in the production of chlorophyll, sugars and starches and regulates stomatal opening in the leaves. The main fertilisers used to supply potassium in hydroponics mixes are potassium nitrate and potassium dihydrogen phosphate. Potassium sulphate and potassium chloride can be used to supply small amounts. Calcium Calcium is used for the manufacture and growth of plant cells. It controls the transport and retention of other elements as well as overall plant strength. The main source of calcium in hydroponics mixes is calcium nitrate. Calcium chloride can be used in small amounts. Magnesium Magnesium is essential for photosynthesis as it is central to the chlorophyll molecule structure. It also helps activate many enzymes required for plant growth. Magnesium is supplied in the hydroponics nutrient solution as magnesium sulphate or magnesium nitrate. Sulphur Sulphur is essential for protein production. It promotes enzyme activation and is a component of some vitamins, improving root growth and seed production. In hydroponics mixes sulphur is supplied as magnesium sulphate, and is often also supplied as part of many micronutrients. 1.4.3. Micronutrients Whilst micronutrients are only needed in very small amounts they are vital to healthy plant growth as they are either involved in photosynthesis or important components of many enzyme processes. Iron Iron is important in both photosynthesis and respiration. It is needed for the plants to make sugars and starches. Iron also has an important role in the activity of many of the enzymes in a plant. Iron is supplied in the nutrient solution most commonly as iron chelate EDTA. There are other types of iron chelates, such as iron EDDHA and iron DTPA which can be used. Iron can also be supplied as iron sulphate. Manganese Manganese is used in chlorophyll and is needed to make enzymes work. It is also used by plants to take up nitrogen. Manganese is supplied in the nutrient solution as with manganese sulphate or manganese chelate. Manganese chloride can also be used. Zinc Zinc is used by the plant to access stored energy. It is also part of enzymes and plant hormones. Zinc is supplied in the nutrient solution as zinc sulphate or zinc chelate.

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Boron Boron is important in flowers and pollen development. Boron is usually supplied in the nutrient solution as sodium borate (borax) or boric acid. Copper Copper is used in a range of plant processes and is a component of enzymes. Copper is supplied in the nutrient solution as either copper sulphate or copper chelate. Molybdenum Molybdenum is used by the plant to process nitrogen. Molybdenum is supplied in the nutrient solution as either sodium molybdate or ammonium molybdate. Chlorine Chlorine is essential for photosynthesis. It activates the enzymes which release oxygen from water. Chlorine is supplied in the nutrient solution, if necessary, with calcium chloride, potassium chloride, or manganese chloride. 1.4.4. Non-essential elements Sodium Sodium is used in the movement of water. Too much sodium in the root zone will cause stress in the plant. Most sources of water will contain a small amount of sodium, but it can also be added as sodium molybdate and sodium borate. Cobalt Cobalt is used by the plant to fix nitrogen. It is not usually added to nutrient solutions. Nickel Nickel is used by the plant to utilize nitrogen. It is not usually added to nutrient solutions. Silicon Silicon is used in the plant for cell walls. It helps to make the plant more robust. There are a range of sources available on the market. 1.4.5. Water Water is essential for plants to live and grow. It enters the plant through the roots and is lost by transpiration from the leaves and stem. Evaporation of water from the leaves (transpiration) helps cool the plant and is also critical to the transport of dissolved mineral nutrients from the soil or nutrient solution from roots to the leaves. Water is also used to carry and distribute complex organic compounds around the plant. This continuous flow of water through the plant provides physical support by keeping the plant turgid.

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As the water evaporates from the leaves, it is exchanges for carbon dioxide, which is used for photosynthesis. How much water is required will depend on the plant type, developmental stage, air temperature, relative humidity and light. 1.4.6. Oxygen Oxygen is required for plant respiration and for water and nutrient uptake. Plant roots grown in water quickly exhaust dissolved oxygen and need additional air which can be supplied by aerating the nutrient solution. 1.4.7. Carbon dioxide Atmospheric carbon dioxide is required as the substrate for plants to convert to glucose through photosynthesis. 1.4.8. Suitable root zone environment Most vegetable crops require a root zone temperature of between 20 and 24˚C. Temperatures that are too high or too low will result in reduced growth and development, increased susceptibility to pests and diseases, and reduced productivity. Root growth is also affected by the concentration of soluble salts (nutrients) in the root zone. The concentration of the soluble salts in the nutrient solution is measured by its electrical conductivity. It is important to measure the EC of the solution in the root zone area. Optimal nutrient concentration varies with plant species and stage of growth. Similarly, the pH of the nutrient solution affects the rate of growth. The availability of each nutrient to the plant varies with the acidity and alkalinity of the soil or nutrient solution. When measuring the nutrient solution pH, it is important to take readings from the root zone. A pH range between 5.5 and 6.5 is suitable for most crops grown hydroponically. 1.4.9. Plant support The soil surrounding the roots physically supports the growing plant. A plant grown hydroponically must be artificially supported which, in traditional media based systems, is provided by the growth media. 1.4.10. Light The amount of light required by plants vary with plant species. Most fruit producing plants required 8 to 10 hours of direct sunlight per day for good production. Plants must be spaced adequately to ensure that each plant receives sufficient light. Excessive light intensity during the summer months can be controlled with additional greenhouse coverings. These should be removed for the winters when light levels are lower. Likewise, dirty and dusty greenhouses will reduce the amount of light plant receive.

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2. The hydroponics system 2.1. Components of the hydroponics system Hydroponics systems require a number of different components to supply water and nutrients to the plants in the correct doses and at the right time, to provide a root zone environment for the plant to grow, and to provide physical support to the plants. These components allow growers to regulate and control the nutrients supplied to the plants and their subsequent growth and production. The key components of a hydroponics system are:

Water supply

Fertigation system

Substrate and other growth and support media

Greenhouse facilities and climate control systems

Power supply 2.2. Water supply All crops require a reliable supply of fresh water to grow. This is especially important with hydroponics systems as the high levels of production needed for a profitable hydroponics operation relies on sufficient high quality fresh water. For commonly produced hydroponics crops such as tomato, cucumber and capsicum, water must have a maximum salinity level below 500ppm (0.78 dS/m) and be free of contaminants. Water sources can include city water supplies and ground water. In circumstances where there is sufficient water of poor quality a reverse osmosis system can be added to the system to remove excess salt and improve water quality. This is generally required in the UAE. A reverse osmosis system uses high pressure to force water through a semi permeable membrane to lower the salt concentration in the water. Reverse osmosis membranes are generally non-porous and will pass water, while retaining most solutes, including ions. The separation of salts and other minerals from the water is achieved by reversing the natural osmotic flow with the application of pressure to the side of the concentrated solution. The process produces a quantity of fresh water and a quantity of brine. Water quality should be regularly monitored for contaminants and concentrations of specific ions and phytotoxic substances. Contamination by microorganisms can be controlled by treating water with UV, ozone and chlorination. 2.3. Fertigation system Fertigation is used extensively in commercial agriculture and horticulture for both field and hydroponically grown vegetables. The fertigation system provides the crop with the water and nutrients they need to grow. This computer controlled system mixes the nutrients according to the predetermined formula, adjusts the pH to the set level, and delivers these to the plants dissolved in the irrigation water. This is done at the required frequency and duration to meet the crop species, growth stage and climatic requirements.

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The type of fertigation system used depends on the size and complexity of the enterprise, the operators’ skill level and the targeted levels of production. The fertigation system consists of the following components:

1. Fresh water storage tanks 2. Nutrient and chemical storage tanks 3. Mixing tank 4. pH meter 5. EC meter 6. Control system 7. Irrigation system 8. Pumps 9. Waste water collection and recycling system

This is illustrated in Figure 1, and each of the components are described below. More detailed information, including specifications for the various components, are given in Appendix 4.3. Figure 1. The basic components of fertigation systems used for hydroponics in the UAE . Fresh water storage tanks Fertigation systems must have a reliable supply of good quality water. The water must be free of contaminants and have a maximum salinity level of 500 ppm (0.78 dS/m). The water storage tanks should hold sufficient water for ???????? Sources of water include city water supply and farm wells (bore water). Water quality should be regularly monitored for contaminants and concentrations of specific ions and phytotoxic substances. 2.3.2. Nutrient concentrates and chemical storage tanks The concentrated mixes of nutrients for the crop are stored in the nutrient storage tanks. Nutrients are premixed into concentrated solutions according to recipes formulated to provide crops all their requirements for growth. These nutrients are mixed with fresh water to make the nutrient solution that supplies the crops with both water and nutrients. Fertigation systems generally have two nutrient storage tanks and one or two pH regulating storage tanks. It is important to have separate nutrient storage tanks for calcium and phosphorus as sources as these are likely to form an insoluble precipitate if mixed together. This will clog irrigation pipes and drippers. Due to the corrosive nature of many fertilisers, tanks are usually made of polyethylene or fiberglass. Where metal tanks are used, they should be either stainless steel or coated with an non-corrosive material such as epoxy. Tanks should be large enough to hold the volume 2.3.1. Fresh water storage tanks Fertigation systems must have a reliable supply of good quality water. The water storage tanks should hold sufficient water for several days of operations. Sources of water include city water supply and farm wells (bore water). Water quality should be regularly monitored for contaminants and concentrations of specific ions and phytotoxic substances.

Figure 1 Fertigation Unit

A B

C D

Recycling system

Flow-through system Water treatment & disposal

Water treatment & reuse

Mixing tank

pH & EC meters

Control unit

Fresh water tank

Irrigation system

Pumps

Pumps & filters

Nutrient & chemical storage tanks

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2.3.2. Nutrient and chemical storage tanks The concentrated mixes of nutrients for the crop are stored in the nutrient storage tanks. Nutrients are premixed into concentrated solutions according to recipes formulated to provide crops all their requirements for growth. These nutrients are mixed with fresh water to make the nutrient solution that supply the crops with both water and nutrients. Fertigation systems generally have two nutrient storage tanks and one or two pH regulating storage tanks. It is important to have separate nutrient storage tanks for calcium and phosphorus as sources as these are likely to form an insoluble precipitate if mixed together. This will clog irrigation pipes and drippers. Due to the corrosive nature of many fertilisers, tanks are usually made of polyethylene or fiberglass. Where metal tanks are used, they should be either stainless steel or coated with a non-corrosive material such as epoxy. Tanks should be large enough to hold the volume of nutrient solution required for at least one fertigation cycle. The accepted system for nutrient storage tanks is:

Tank A - used for storing calcium-based nutrient solutions

Tank B - used for storing phosphorus-based nutrient solutions

Tank C - used for storing the acid to decrease the pH

Tank D - used for storing the base solutions to increase the pH Acid solutions, used to reduce pH, include nitric acid, phosphoric acid and sulphuric acid. Alkaline solutions, used to increase pH, include potassium hydroxide and potassium bicarbonate 2.3.3. Mixing tank The nutrient concentrates from the nutrient storage tanks are mixed with fresh water in the mixing tank to produce the nutrient solution. The concentrations of nutrients, and the pH are continuously monitored in the mixing tank and the amounts of nutrients added adjusted to ensure the nutrient solution is the correct pH and contains the correct concentration of nutrients. In hydroponics systems that use recycled runoff water this is also added back into the system through the mixing tank. Mixing tanks can be large tanks where a batch of nutrient solution is mixed prior to delivery to the crop, or a series of small tanks from which the nutrient solution is continually drawn, mixed and adjusted as it is being delivered to the crop. 2.3.4. pH meter Fertigation systems contain a pH meter in the mixing tank to constantly measure the pH of the nutrient solution and adjust it to meet the requirements. The pH is important as the optimal uptake of nutrients by crops is pH dependent. 2.3.5. EC meter Fertigation systems contain an EC meter in the mixing tank to constantly measure the EC of the nutrient solution and adjust it to meet the requirements. The EC is a measure of the total dissolved minerals salts in the nutrient solution. This is important as it determines the nutrients that are provided to the crop.

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3.3.6. Control unit The fertigation system is run by the control unit. It monitors the EC and pH and adjusts them to meet the formulated specifications. It also regulates the irrigation frequency and duration. Water quality and nutrient solution requirements for hydroponic systems vary according to the crops to be grown. Optimum results can be achieved when automated irrigation, fertigation and greenhouse environment are used. Control units available include those that:

Allow irrigation pumps to be turned on at pre-set times

Allow irrigation sections to be turned on or off, according to a pre-determined schedule

2.3.7. Irrigation system Water and nutrients are delivered to the individual plants from the mixing tank by the irrigation system. It consists of pumps, pipes and drippers that ensure each plant gets the same amount of water and nutrients. This is further described in Section 2.4. 2.3.8. Pumps Fertigation systems contain many pumps. These are needed to move concentrated mineral solutions from the nutrient storage tanks to the mixing tank, to bring fresh water to the mixing tanks, and then to distribute the nutrient solution to the crop. Pumps are also needed to bring runoff water back to the runoff water storage tank. 2.3.9. Run off water recycling system To increase the efficiency of water and nutrient use, runoff water can be recycled back into the system. This requires runoff water to be collected, treated and the stored. The treatment is a three stage process that firstly uses sand and screen filters to remove large particles, then passes the water through a UV filter to kill any pathogens. This water is then stored in the recycled water tank. Up to one third of the crops water supply can be provided by recycled water. 2.4. Delivering the nutrient solution to the crops The nutrient solution containing the dissolved mineral salts required for optimum plant growth is delivered to the crops by the irrigation system. The various pumps in the fertigation system are used to inject the nutrient solution into the irrigation system and deliver the required levels of dissolved mineral salts and water to the plants. 2.4.1. Injection equipment and application methods There are two types of nutrient (fertiliser) injection: quantitative and proportional. Quantitative A calculated amount (batch) of pre-mixed nutrient solution is stored in the mixing tank and subsequently applied to each irrigation block. This method is suited to automation and allows for accurate nutrient placement.

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Proportional Nutrients are applied by direct injection into the flow of irrigation water in a constant ratio, proportional to the water discharge rate. This method of nutrient application is generally used in hydroponics in the UAE as it allows for increased fertigation during periods of high water demand when most nutrients are required. Nutrients can be injected into the irrigation system either using pumps or a pressure differential between nutrient tanks. It is important to select the correct injection equipment as it affects the efficient operation of the irrigation system and the effectiveness of the nutrients. The three most widely methods of injection are:

1. Suction injection 2. Pressure differential injection 3. Pump injection

2.4.2. Suction injection In this method, the pumping unit develops a negative pressure in its suction pipe and this is used to draw nutrient solutions from an open supply tank into the suction pipe. The rate of delivery is controlled by a valve. Another hose or pipe connected to the discharge side of the pump fills the supply tank with water. This inflow to the tank can be regulated with a high-pressure float valve. A direct-acting solenoid valve can be used to automate this system. This system is ideal for dry formulations as concentrated nutrient solutions do not have to be pre-mixed. It is simple to use and requires little maintenance. However, if the tank operation starts when irrigation is commenced, the concentration of the nutrient solution will decrease as the fertilisers get dissolved. This, in turn, will place most nutrients below the root zone. All fittings must be airtight to avoid suction air entering the pump. Installation of a check valve is necessary to avoid contamination of the water supply by chemical flow back down the suction pipe when the pumping unit stops. 2.4.3. Pressure differential injection In this method, the inlet of a batch tank is connected to the irrigation system at a point of pressure higher than that of the outlet connection. The pressure differential causes the irrigation water to flow through the batch tank containing the fertiliser to be injected. As the irrigation water passes through the tank, a varying amount of dissolved fertiliser is carried downstream irrigation system. This system is simple to operate and ideal for dry formulations. However, it has the effect of decreasing the nutrient solution concentration as the fertiliser dissolves, leading to poor nutrient placement. It requires pressure loss in the main irrigation line and the tanks must be capable of withstanding the irrigation system operating pressure. Batch tanks are ideal for use if nutrient concentration during injection is not critical as proportional fertigation is not possible using this system.

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It is possible to install a pressure differential system called Venturi system as a bypass or inline. They create a constriction in the pipe flow area resulting in negative pressure or suction which draws the nutrient solution into the line. Using this device, it is possible to achieve irrigation rates of 2 to 3 thousand liters per hour and to control the fertiliser rate with some degree of accuracy. However, it requires up to 33% pressure loss in the main irrigation line, making automation and quantitative fertigation difficult. 2.4.4. Pump injection This is the most common method of injection. Fertilisers are delivered from the supply tank into the pressured mainline using either electric or hydraulic pump injection. Electric pumps Electric pumps include single or multiple piston, diaphragm, gear and roller pumps. The electric pump injection method is simple, accurate and effective, with no pressure loss in the main irrigation line. It is possible to do either proportional or quantitative fertigation. However electrical injection requires an electric power source to operate and pumps must develop a minimum mainline pressure to operate. Piston-activated hydraulic pumps Piston activated hydraulic pumps use a hydraulic motor to pump fertiliser solution into the mainline system. The maximum rate of injection is proportional to the pressure in the mainline. This system allows for accurate injection rates. Rates of up to 320 liters per hour are achievable. Two or more units can be operated in parallel for high injection rates. Diaphragm-activated hydraulic pumps Diaphragm-activated hydraulic pumps use water pumped into the lower chamber to force up a rubber diaphragm in the drive unit. Fertiliser is forced out of the injector into the irrigation system. Piston-activated and diaphragm hydraulic pumps are easy to install, operate and maintain and can be used for either proportional or quantitative irrigation. The rate of injection is adjustable and automation is easily achievable. However, they require a large number of working components and are sensitive to air pockets, as pistons or diaphragms need a continuous water discharge to operate. 2.5. Plant growth systems There are essentially two types of growth systems and support media used in hydroponics:

1. Plants are grown in a substrate which provides both physical support and the root environment required.

2. Plants are grown in water with no supporting medium for the roots, with the plants supported by floating platforms and the roots growing directly in the nutrient solution.

These are illustrated in Figure 2.

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Figure 2. Different types of growth systems and support media

2.5.1. Water culture systems

In this type of hydroponic system, plants are grown on and supported by floating platforms, usually made of Styrofoam and roots grow directly in the nutrient solution. Air is supplied by natural aeration or a pump that bubbles the nutrient solution, supplying oxygen to the roots. Water culture systems are closed systems. They are water and fertiliser efficient, and environmentally sustainable. The three most widely used types of water hydroponic systems are:

1. Nutrient film technique 2. Deep flow systems 3. Aeroponics

Nutrient film technique

Plants are placed in a polypropylene-treated PVC pipes or troughs, through which a thin film of nutrient solution flows. Plants are suspended through holes in the trough, which is gently sloped so the nutrient solution is pulled back by gravity to the nutrient container.

Hydroponics production systems

Water culture Substrate

Nutrient film Deep flow Aeroponics

Inorganic Mixtures

Perlite

e

Vermiculite

Rockwool

Sand/gravel

Other

s

Organic

Sawdust

Peat moss

Reed/sedge peat

Coco peat

Other

s

Range of organic and inorganic mixtures

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The shallow stream of water containing the dissolved nutrients is re-circulated past the thick root mat that develops at the bottom of the channel. The upper surface of the mat is kept moist whilst receiving oxygen for growth. When growing crops using the Nutrient Film Technique (NFT) it is important to:

Ensure the nutrient solution flows as a thin ‘film’ of water

Ensure the channels are not too long or nutrients and oxygen may run out

Monitor water temperature, as temperature increases, oxygen levels decrease

Monitor EC and pH of the nutrient solution in the root zone at least once a day Deep flow systems Deep flow hydroponics is the most commonly used soilless system. Plants are supported over a reservoir of nutrient solution so that their roots grow into the solution. Rectangular tanks made from, or lined with, plastic are generally used for this system. The nutrient solution must be well aerated and routinely monitored to ensure the appropriate nutrient balance is maintained, particularly in the root zone environment.

Aeroponics systems Aeroponics is a system in which plant roots remain suspended in an enclosed growing chamber, where they are sprayed with a fog or mist of nutrient solution at short intervals (usually every few minutes). Growing media is only used for initial plant establishment. Young plants can be propagated in small containers of growing media, with the roots growing out into the sealed area sprayed with the nutrient mist.

2.5.2. Substrate or aggregate systems Substrate or aggregate systems use an inert growing medium to support and surround the roots. Plants are grown in bags, pots or other containers filled with the substrate or growing medium, placed in rows and irrigated with nutrient solution through the fertigation system. Substrate systems offer the most appropriate level of technology for smallholder hydroponic producers in Abu Dhabi Emirate. In this system, substrates provide the root zone environment the plants need to grow, as well as the physical support plants need. The advantage of using substrate over soil include:

1. Good water holding capacity 2. Low soluble salt level 3. Suitable pH (range of 5.5 – 6.5) 4. Provide a sterile media, free microorganisms and other contaminants 5. Long term compaction and decomposition stability 6. Resistant to chemical and heat treatment 7. Ease of handling 8. Local availability

2.6. Types of media for substrate hydroponics Substrate media can either be organic or inorganic.

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2.6.1. Inorganic Perlite This is a silicon mineral of volcanic origin. Lightness and uniformity make perlite very useful for increasing aeration and drainage. It is an effective an amendment for growing media. Vermiculite The ore is a mica-like silicate mineral. It is ground and heated and the resulting product is a lightweight granule containing numerous thin plates which have a large surface area, giving this substrate a very high water holding capacity. There are many negative charged sites on the plates giving this substrate a high cation exchange capacity. Vermiculite also provides good aeration and drainage, as well as the ability to supply potassium and magnesium. Rockwool Rockwool is produced by heating basalt, limestone, and coke at very high temperatures. Once the mixture liquefies it is spun at high speed into thin fibers. The fibers are later heated with additives, bound together, and pressed into blocks or slabs which are extensively used in hydroponics. It is an inert material with a negligible cation exchange capacity and little effect on substrate pH. Rockwool provides good aeration and drainage, while also increasing water holding capacity. It is widely used in hydroponics and recommended for use in UAE. Sand or Gravel Sand and gravel are basic components of soil, with particle sizes ranging from 0.02 to 2 mm in diameter and usually added to substrate media to increase bulk density. It has low cation exchange capacity, low water holding capacity, and little effect on pH. 2.6.2. Organic Sawdust The tree species from which sawdust is derived largely determines its quality and value for use in growing media. Sawdust has a high carbon to nitrogen ratio and must be thoroughly composted before use to avoid nitrogen immobilization in the compost. It may also contain phytotoxic resins and tannins, even after composting. The high cellulose and lignin content along with insufficient nitrogen supplies create depletion problems that restrict plant growth. Peat moss Peat moss is formed as a result of plant decomposition under cool temperatures in poorly drained areas. The type of plant material and degree of decomposition largely determine its value for use in growing media. There are different types of peat moss according to the degree of decomposition. Sphagnum peat moss

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This is derived from the dehydration of acid swamp plants from the genus Sphagnum. It has a very high water holding capacity, holding up to 60% of its volume in water. It contains approximately 95% organic matter and 75% fiber and a high cation exchange capacity. However, it has a pH of 3.0 – 4.0 and liming may be required when using it as a growing medium. It is the most desirable form of organic matter for preparation growing media. Coco peat Coir fiber or pith is a natural and renewable resource produced from coconut husks. The husks are ground, long and medium fibers removed, the remaining coir consisting of a granular pith with short fibers. It has high nutrient and water holding capacities but has a low cation exchange capacity. With a pH of 5.7 -6.5 liming is not required. 2.6.3. Other There are a range of other substrates that can be used for hydroponics, including mixtures of inorganic and organic media. 2.7. Types of substrate hydroponics systems

The two most widely used types of substrate hydroponics systems are:

1. Bag or container culture 2. Ebb and flow (flood and drain) system

2.7.1. Bag or container culture The bag or container system is the most common type of substrate culture used. The containers are filled with a growing medium, placed in rows, and irrigated with nutrient solution using drippers, emitters or micro sprinklers. A timer activates a submersed pump and the nutrient solution is either dripped onto the base of the plants by a drip line or emitters or sprayed onto the plants by micro sprinklers. The systems can either be closed or open. For open systems, the excess nutrient solution drains out from the bottom of the container and is collected and drained away from the crop. In this system, an excess of 10-40% irrigation solution is used to leach and flush the medium. The excess nutrient solution can alternatively be recovered (closed system) and reused. 2.7.2. Ebb and flow (flood and drain) In this system, the growing media is flooded with the nutrient solution by a submerged pump connected to a timer and then allowed to drain. This cycle is repeated several times a day, depending on the crop, age of plants, and growing environment. Large growing trays filled with gravel, grow rocks or granular rock wool are routinely used in these systems. Alternatively, pots or other containers can be placed in flooding bays. 2.8. Greenhouse facilities and climate control systems Hydroponically grown crops can either be grown directly in open fields or in greenhouses, depending on the scale of production required.

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Greenhouse facilities are often used in hydroponic production systems, as they protect the plants from harsh environmental conditions and provide the plants with the required climatic conditions they need to achieve the maximum growth rates. Daytime and nighttime temperature, light distribution, humidity and air movement are all controlled, so the plants have the optimum conditions for growth. This results in stronger, more disease resistant, and productive plants. Climate control systems are used to adjust the temperature and humidity inside the greenhouses to the optimum levels required by the different crop species to be grown and their stage of growth. This greater control of climatic conditions in the plant growing environment often allows crop production throughout the year, independently of the seasons. Evaporative cooling systems are generally used for greenhouses in the UAE. Under high temperatures (above 400C) and low relative humidity (below 30%) the consumption of water for evaporative cooling will be around 6.5 m3 per hour for an 8 m span greenhouse (approx. 300m2). During times of high water use for cooling it is important to keep the fresh water supply running constantly, to compensate for the water loss in evaporation through the cooling pads. To avoid concentration of water minerals, which will result in a the build of salt on the pad surface causing pressure drop, some of the recirculation water must be discharged and replaced by fresh water from time to time. The water tank capacity to cool eight greenhouses with 8 m span is approx. 4,000 – 5,000 gallons. See appendix 4.1 and 4.2 for further information.

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3. Management of the hydroponics system 3.1. Choosing the correct substrate The growing medium provides the plant with:

Physical support

A reservoir of water (water retention and availability)

A reservoir of nutrients in the root zone

Air porosity to allow gas exchange The availability of water for plant growth is largely determined by how tightly the water is held by the solid components of the growth medium. The closer the water molecule is to a solid component, the more tightly it is held. Growth media containing fine mixes can hold more water than those with coarser mixes. The nutrients in solution in the form of ions are absorbed by the root cells, either passively (directly carried to roots by fertigation water for plants grown in water culture systems), or actively (cell membrane transport of ions into root cells). Adequate gas exchange at the root zone is essential for plant growth. This is an important consideration when selecting substrates for hydroponics. The types of growth media have already been described in Section 2.6. The following should be taken into consideration when choosing the growth medium for hydroponics: Chemical properties of the substrate

Substrate acidity or alkalinity (pH)

Substrate salinity (EC)

C:N ratio (degree of decomposition)

Cation exchange capacity Physical properties of the substrate

Bulk density

Porosity (pore space for aeration and water retention)

Particle size distribution

Water holding capacity Each of these is described below. 3.1.1. Substrate pH The substrate’s pH directly affects the availability of macro and micronutrients. An evaluation of pH for soilless growing media is given in Table 1, whilst Table 2 summarizes methods to control pH in growing media.

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Table 1. An evaluation of pH for soilless growing media

Extremely low 4.5 or less

Very low 4.6 - 4.7

Low 4.8 – 4.9

Slightly low 5.0 – 5.1

Optimum 5.2 – 5.5

Slightly high 5.6 – 5.8

High 5.9 – 6.3

Very high 6.4 – 6.8

Extremely high 6.9 and higher

Table 2. How to control pH in growing media

To lower pH To raise pH

Add acid to the water (neutralizing of alkalinity), acidification

Stop adding acid to irrigation water

Stop the use of basic fertilisers (e.g. calcium nitrate) and start the use of acidic fertilisers to lower pH

Use basic fertilisers to raise substrate pH

In severe cases, drenching with aluminum sulphate or iron sulphate to rapidly lower pH

In severe cases, injecting potassium bicarbonate to increase the alkalinity of irrigation water to increase substrate solution pH

Nitric, phosphoric and sulphuric acids can be used to lower pH. The criteria used for selecting the appropriate acid are: cost, availability, handling and ion required for injection (N, P or S). For more details see Section 3.2.

3.1.2. Substrate EC Salinity is expressed as electric conductivity (EC) which is a relative measure of the total quantity of salts dissolved in the water. Table 3 describes the range of suitable water for irrigating plants in hydroponic production systems. Figure 3 gives corrective measures for adjusting soluble salt and pH problems.

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Table 3: Suitability of water for irrigation of hydroponic systems

Water classification

Electric conductivity (mmhos/cm)

Total dissolved solids(salts) (mg/l,ppm)

Sodium (%of total solids)

Boron (mg/l,ppm)

Excellent <0.25 <175 <20 <0.33

Good 0.25-0.75 175-525 20-40 0.33-0.67

Permissible 0.75-2.0 525-1400 40-60 0.67-1.00

Doubtful 2.0-3.0 1400-2100 60-80 1.00-1.25

Unsuitable >3.0 >2100 >80 >1.25

Figure 3. Corrective measures for adjusting soluble salt and pH problems

3.1.3. Substrate C:N ratio Microorganisms require nitrogen to break down organic matter. They generally require a ratio of 25:1 or 1 nitrogen atom for every 25 carbon atoms they utilize. If a growing medium has a C:N ratio of less than 25:1 enough nitrogen is available from the organic matter to meet the microorganisms needs. However, a C:N ratio higher than 25:1 will result in depletion of nitrogen from the environment and a direct competition between microorganisms and the plant for nitrogen from the fertilisers. Growth substrates should have a maximum C:N ratio of 30:1 to avoid nitrogen tie-ups.

Growing medium

pH

Soluble salts

High

High

Low

Low

Acid injection Leach Iron sulphate

Base injection Dolomitic lime Calcium carbonate Hydrated lime

More frequent irrigation Longer irrigation interval

Less frequent irrigation Shorter irrigation intervals

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3.1.4. Substrate cation exchange capacity (CEC) Cation exchange capacity is the sum of total exchangeable cations that a substrate or soil can adsorb. Negative charges in the growing media hold positive charged ions from nutrients (fertilisers). A medium and high cation exchange capacity will require less frequent application of nutrients than a media with low CEC. Peat has reasonably high CEC. Sand and sawdust have low CEC values and thus likely to produce high leaching losses in fertilisers. The optimum CEC for container plants is in the range of 10-30 me/100g dry weight of material. 3.1.5. Substrate bulk density Dry weight per given volume, g/cm³: Bulk density = Dry weight gm/cm³ Volume Growing media are generally composed of more than one ingredient, each contributing to the bulk density of the growing medium. Loose porous growing media have a lower bulk density than heavy compacted media. This larger amount of pore space provides good aeration for the roots. As bulk density increases the total pore space decreases. When heavy coarse aggregates are mixed with lightweight organic matter, bulk density increases and porosity and percolation rates decrease. However the bulk density of the growing medium must be high enough to provide adequate support for the plant. 3.1.6. Substrate pore space Total pore space is a measure of the volume of the growing medium that is filled with water and with air, or the ability to hold air and water. Pore size determines the rate of drainage and gas exchange. Total porosity is important but aeration porosity should always be considered when choosing growth media. A growing medium with a high total porosity could have uniformly small pores and thus hold a great deal of water and very little air. Another medium with the same total porosity, but with large pores might hold much more air and less water. 3.1.7. Substrate particle size distribution

The percentage of fine to course particles in the substrate that affects the water retention and air circulation. The stability of particle sizes of the different substrate components is important to maintain its physical properties.

3.1.8. Substrate water holding capacity Water holding capacity (field capacity or container capacity) refers to the amount of water that can be held in the soil and the growing medium by capillary force and available for uptake by the plant.

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3.1.9. Overall considerations Overall, the substrate must provide a balance between materials that provide aeration, good water holding capacity and drainage. See Table 4 for further details. Table 4. Physical and chemical characteristics of materials used in soilless culture

Material Bulk density (weight)

Water holding capacity

PH porosity Cation exchange capacity

Decomposition rate (carbon: Nitrogen)

Sawdust L H 7.0 M H H

Rice hulls L L L H M M-H

Shaving L M L H M M-H

Vermiculite L H variable M H L

Peat moss L H 3.0-4.0 H H M

Perlite L H neutral H L L

Coir L H 4.9-6.8 H M L

Polystyrene foam

L L Neutral H L L

Bark L M L M M M

sand H L variable M L L

Explanation of categorization

Low 0.25 gm./cm³

20% 3- 4.5 5% 10 meg/100 cm³

1:200

Medium 0.25-0.75

20-60% 5- 6.5 5-30% 10-100 1:200-1:500

High 0.75 60% 6.5-8.5 30% 100 1:500

3.2. Hydroponics chemistry and using the fertigation system The fertigation control unit manages the pH and content of the pre-mixed nutrient concentrate solutions and adjusts the amount of water, nutrient mixes from both tanks and acid or base to be added to the mixing tank. These are combined to form the nutrient solution which is injected into the irrigation system and delivered to individual plants. This ensures the plants receive the correct amount of nutrients required for optimum growth. The concentration and chemical content of the nutrient solution varies according to crop type, stage of growth as well as environmental conditions such as temperature and humidity. 3.2.1. Preparing the nutrient concentration and the nutrient solution supplied to the crops Fertilisers containing calcium sources should be stored separately from phosphorus sources. Negatively charge ions (anions) from one fertiliser can react with positively charged ions (cations) from another fertiliser, to form an insoluble precipitate. This can lead to the clogging of the irrigation lines. When using phosphate fertilisers in combination with calcium and magnesium precipitation of insoluble phosphates occurs if the pH of the irrigation water

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is higher than 7.5. Acidifying the irrigation water with sulfuric or phosphoric acid lowers irrigation water pH and minimizes precipitation and clogging of lines. 3.2.2. Chemical composition of the calcium based fertiliser in tank A Calcium nitrate, potassium nitrate, ammonium nitrate, and iron are usually added to tank A. Calcium nitrate Calcium nitrate is relatively soluble in water causing only a small shift in the water pH. However, if the irrigation water contains high levels of bicarbonate, precipitation of calcium carbonate (lime) may occur. Potassium nitrate Potassium nitrate is very soluble in water and provides an additional source of nitrogen. It can be used as a replacement for potassium chloride for crops sensitive to chloride. Ammonium nitrate Ammonium nitrate is very soluble in water and an additional source of nitrogen. When ammonium nitrate, calcium nitrate, and potassium nitrate are dissolved the heat generated is absorbed by the water and a very cold solution results. Dissolving the fertiliser to the desired concentration may take longer as this solution will need to stand until it reaches the temperature required for the mixture to dissolve. Chelated iron Iron, like other micronutrients is supplied to the plants as chelates. Micronutrients in chelated form have a greater plant bioavailability as they are more stable in solution and better able to stand pH variations. See Section 3.4 for further information on hydroponics nutrition and crop nutrient calculations. 3.2.3. Chemical composition of the phosphorus based fertiliser in tank B Phosphorus source, magnesium sulfate, micronutrients and potassium chloride or potassium nitrate are usually added to tank B. Phosphorus source The most common fertilisers used to supply phosphorus are mono-ammonium phosphate and potassium dihydrogen phosphate. Magnesium sulphate Magnesium sulphate has good water solubility and is used as a source of Mg to the crop. Care should be taken to ensure the appropriate amount is applied to avoid phytotoxicity.

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Compatibility with other fertilisers should also be checked to avoid precipitation and clogging of irrigation lines. See Section 3.4 for further information on hydroponics nutrition and crop nutrient calculations. 3.2.4. Nutrient solution supplied to crops The nutrient composition, concentration, temperature and pH of the nutrient solution must be regularly monitored not only in the mixing tank, but after it has been injected into the irrigation system and reached the root zone. Ensure fertiliser solutions being mixed are compatible and properly dissolved avoiding precipitation of insoluble chemicals and clogging of the fertigation system. If the nutrient solution is recirculated, care should be taken to avoid sodium accumulation as it can cause phytotoxicity to plants at high concentrations. 3.2.5. Mixing the nutrients Nutrient solutions can either be mixed manually or by an automated system. Manual mixing of nutrients can be done in two ways:

1. Mixing the nutrient solution directly in a mixing tank from individual pre-mixed dry or liquid nutrient concentrates

A single large tank is used to make up a batch of nutrient solution. The following steps should be followed when mixing fertilisers:

Fill in the mixing tank with 50-75% of the required water to be used for mixing the nutrient solution, if mixing concentrated dry (powder) pre-mixes of soluble nutrients

When using both dry and liquid pre-mixed concentrated nutrients, always add the liquid nutrient mix to the water before adding dry, soluble mixes

When mixing dry nutrient concentrates always add the dry ingredients slowly, and mix thoroughly to ensure they are properly dissolved. This will prevent clogging of the irrigation lines by large, insoluble or slowly soluble lumps

Always put acid into water, not water into acid.

2. Making up two nutrient concentrate solutions from pre-mixed dry nutrient concentrates in separate storage tanks A and B, then diluting them in the mixing tank to make a nutrient solution supplied to crops:

Mix up the A tank (calcium source) pre-mixed dry nutrient concentrate with water to make a concentrated nutrient solution in a small tank or drum. And a B tank (phosphorus source) pre-mixed dry nutrient concentrate with water to make a concentrated nutrient solution in another small tank or drum.

Add equal amounts of the A and B tanks concentrate solutions to a larger mixing tank at the appropriate ratio to make the nutrient solution to be delivered to the plants.

Do not mix concentrated nutrient solutions directly with each other. Add each concentrate to the water and mix thoroughly before adding the next.

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3.3. Electrical conductivity and pH control The electrical conductivity and pH of the nutrient solution must be checked at least once a day. They must be kept within the range suitable for the particular crop grown. It is important to check the EC and pH of the nutrient solution in the root zone as well as in the nutrient mixing tank. 3.3.1. Electrical conductivity Electrical Conductivity (EC) is a measure of the total dissolved mineral salts (nutrients) in the solution (expressed as how well the solution carries an electrical current). The concentration of a nutrient solution affects plant growth, development, and production. Electrical conductivity is measured with an EC meter and expressed as milliSiemens per centimetre (mS/cm) or deciSiemens per metre (dS/m). The higher the salt levels in the solution, the higher the EC. 1 mS/cm = 1 dS/m The EC of a solution can also be expressed as: 1. Total dissolved solids (TDS) measured in parts per million (ppm), an EC reading of 1

mS/cm = 640 ppm 2. Conductivity factor (cF), an EC reading of 1 mS/cm ≈ 10 cF It is important to be clear about the unit of measurement used. For example, a cF reading of 10 represents a weak nutrient solution, whilst an EC reading of 10 represents a strong solution. 3.3.2. pH pH is a measure of the relative acidity or alkalinity of a solution. It refers to the relationship between the concentration of free ions H+ and OH- present in a solution and ranges between 0 and 14. If the pH is below 7, the solution is acidic. If the pH is above 7, it is alkaline. A pH of 7 means that the solution is neutral. The pH affects nutrient availability to the plants. Nutrient solutions must contain ions in solution and in chemical forms that can be absorbed by plants. In hydroponic systems plant productivity is closely related to nutrient uptake which is affected by pH regulation. Individual nutrients in solution show a different response to changes in pH. The pH range for hydroponics production is between 5.5 and 6.5. Figure 3 shows the effect of substrate or soil pH on nutrient availability and element toxicity. The width of the horizontal bars represents the availability of elements at any given pH.

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Figure 3. Diagram of the effect of substrate or soil pH on nutrient availability and element toxicity (from Fernandez & Hoeft, 2009)

The pH of a solution can be increased or decreased by adding an alkaline or acid solution, respectively. The most commonly used acid used is phosphoric acid. Nitric acid can also be used but should be handled with extreme care as it is a highly corrosive and strong acid. Adding large amounts of acid to the nutrient solution will change the chemical composition of the final solution. For example, adding phosphoric acid or nitric acid will increase the amounts of phosphorus and nitrogen in the nutrient solution. A combination acid (made up of phosphoric and nitric acid) can used to keep these elements in balance. In most situations, adding a small amount of acid to the nutrient solution does not result in any significant changes in chemical composition. Alkaline solutions are used to increase the pH. Slated lime (Ca (OH) 2) is often used or alternatively, potassium hydroxide (KOH). Potassium hydroxide is usually purchased as pellets and should be made up into a low concentration solution first, such as a 5% solution. The diluted alkaline solution can be used to adjust the pH. Potassium hydroxide should be handled with care as it is corrosive and can damage skin and clothing.

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Minor adjustments in the pH of nutrient solutions can be made by changing the form in which nitrogen (N) is supplied. For example, nitrogen can be supplied as ammonia (which lowers pH) or nitrate (which increases pH). 3.4. Hydroponics nutrition and crop nutrient calculations 3.4.1. Nutrient composition of the hydroponics solution The first requirement is to test the composition of the water used for the nutrient solution, to determine which nutrients are already present in the water, and to what extent. For example, hard water from bores might have high levels of calcium and magnesium. In which case the additional requirements for these nutrients will be reduced. In many cases, a standard mixture of nutrients can be used for most or many vegetable crops. The important thing it to make sure that the pH and EC of the solution are correct, as described in Section 3.3. Small variations in the actual amounts of fertiliser used will not make a big difference unless there has been too little or much of any nutrient added to the mixture. However, standard recipes do not always provide the optimal balance of nutrients for a given crop or under particular conditions. Different mixtures can be used at different stages of a crop to manage the plant more closely. A standard mixture will not supply the right balance of nutrients for all crops and conditions. While a standard mixture can be used to successfully grow a crop, for optimal production a more precise nutrient management is often needed. 3.4.2 Examples of nutrient mixtures Some common nutrient amounts and example mixes are given in Table 5. These are intended as a guide and are not the actual recommended mixtures, although most commercially available mixtures would fit within these figures. In addition to these, some of the common ratios in nutrient solutions are shown in Table 6. These ratios are important components of the overall balance of the mixture. Advice and guidance should be sought from extension specialists at the Abu Dhabi Farmers’ Services Centre to determine the optimal mixture for particular hydroponic growing systems in the UAE.

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Table 5. Sample nutrient amounts and example mixtures

Nutrient Common nutrient amounts (g/KL or mg/L or ppm)

Example mixtures (g/KL or mg/L or ppm)

Nitrogen (NO3-) 50 - 500 200

Nitrogen (NH4+) 0 - 150 10

Phosphorus 15 - 200 40

Potassium 50 - 500 180

Calcium 80 - 400 150

Magnesium 25 - 100 30

Sulphur 20 - 240 40

Iron 1 - 10 3

Manganese 0.1 - 5 0.3

Boron 0.05 - 5 0.3

Zinc 0.04 - 5 0.1

Copper 0.02 - 1 0.05

Molybdenum 0.001 – 0.05 0.05

Table 6. Common nutrient ratios

Potassium: Nitrogen Calcium: Nitrogen Potassium: Calcium

1:1 1:1 1:1

2:1 1:2 2:1

1.5:1 0.75:1 1.5:1

3.4.3. Calculating the amount of fertiliser to use To calculate the amount of fertiliser to use, the percentage of the specific nutrients in the fertiliser needs to be determine. These are given in Table 7. The nutrients to be used also need to be known. The sample mixture given in Table 5 is expressed in grams per kiloliter (g/kL). This is the same as milligrams per liter (mg/L) and parts per million (ppm). For example 200 g/kL equals 200 ppm. Often minor nutrients are shown as percentages. To change a percentage to ppm, multiply the percentage in the decimal form by 10,000. For example, 1% in the decimal form is 0.01. To convert to ppm, multiply by 10,000, so 1% = 100 ppm. To convert ppm to a percentage, divide ppm by 10,000. There are two important equations to use:

1. To find out the amount of fertiliser needed Amount of nutrient x 100 (g/kL or ppm) Percentage of nutrient in fertiliser (from Table 7)

2. To find out how much of a nutrient is given in a specific amount of fertiliser Amount of fertiliser x Percentage of nutrient in fertiliser (from Table 7) (g/kL or ppm) 100

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3.4.4. Calculating the amount of nutrient in the fertiliser The percentage of a nutrient in a fertiliser is calculated from the atomic weight of the nutrient and the atomic weight of the fertiliser molecule. This percentage will change between different fertiliser products. Common percentages of nutrients are given in Table 7. Table 7. Fertilisers used in hydroponics and their nutrient percentages

Fertiliser Nutrient percentages (%)

N (NO3)

N (NH4)

Ca P K S Mg Mn Zn Fe B Cu Mo

Calcium nitrate 14.5 1.0 18.8

Ammonium nitrate

17.5 17.5

Ammonium sulphate

21.2

Mono-potassium phosphate (MKP)

22.8 28.7

Mono-ammonium phosphate (MAP)

12.2 27.0

Di-ammonium phosphate (DAP)

21.2 23.5

Potassium nitrate 13.8 38.7

Potassium sulphate

44.8 18.4

Magnesium sulphate

13.0 9.8

Magnesium nitrate

10.4 9.5

Iron chelate* 15.3

Manganese sulphate

32.5

Manganese chloride

27.7

Zinc sulphate 22.7

Borax 11.5

Boric acid 17.7

Copper sulphate 25.6

Sodium molybdate

39.7

Ammonium molybdate

53.0

(* Iron chelate is available in a range of different product formulations. Commercial suppliers will have information about the iron percentage for each product). 3.4.5. Example of nutrient and fertiliser calculations The easiest way to calculate what is needed in the mixture is to start with the macronutrients, sulphur, magnesium, and calcium. Then work out the nitrogen, phosphorus and potassium levels, before doing the micronutrients. Again, it is important to first check the nutrient status of the water source before calculating what additional nutrients to add. Also note that adding acid or base to adjust pH can add other amounts of nutrient to the mixture.

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For example, if the sample mixture in Table 5 was being used, and the water supply already had 40 g/kL of calcium, then only 150-40 = 110 g/kL of calcium need to be added. This example uses the nutrient percentages in Table 7 and the sample mixture from Table 5. To add sulphur & magnesium, using magnesium sulphate Using equation 1: Amount of nutrient x 100 (from Table 5) Percentage of nutrient in fertiliser (from Table 7)

40 x 100 13

= 307.69 g This shows that 307.69 grams of magnesium sulphate needs to be added per 1,000 liters of nutrient solution. Some magnesium is also present. Use equation 2 to calculate the amount. Amount of fertiliser x Percentage of nutrient in fertiliser (from Table 7) (from above) 100

307.69 x 9.8 100

= 30.15 g This is close enough to the chosen mixture. This shows that 307.69 grams of magnesium sulphate in 1,000 liters of water gives enough sulphur and magnesium for this nutrient solution. To add calcium and nitrogen, using calcium nitrate Using equation 1:

150 x 100 18.8

= 797.87 g This will also add some nitrogen, in both an ammonium (NH4) and nitrate (NO3) form. Use equation 2 to work out how much in each form. Nitrogen as ammonium:

797.87 x 1.0 100

= 7.98 g Nitrogen as nitrate:

797.87 x 14.5 100

= 115.69 g

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This shows that another 10 – 7.98 = 2.02 g of N as NH4, and 200 – 115.69 = 84.31 of N as NO3

will need to be added. Ammonium nitrate can be used to complete the ammonium and equation 1 can be used to work out how much to add.

2.02 x 100 17.5

= 11.54 g So, by adding 11.54 grams of this fertiliser there will be enough ammonium and this will also add another 2.02 grams of nitrate nitrogen (using equation 2). This means that 84.31 – 2.02 = 82.29 grams of nitrogen as nitrate still needs to be added. This will be dealt with later. To add phosphorus and potassium, using mono-potassium phosphate (MKP) Using equation 1:

40 x 100 22.8

= 175.44 g This shows that 175.44 grams of mono-potassium phosphate per 1,000 liters of solution needs to be added. Potassium (50.35 grams) is also added. Using equation 2:

175.44 x 28.7 100

= 50.35 g But 230 – 50.35 = 179.65 grams more potassium still needs to be added. Potassium nitrate can be used to add this. Using equation 1:

179.65 x 100 38.7

= 464.21 g This will also add (equation 2) another 64.06 grams of nitrogen (N), but 82.29 – 64.06 = 18.23 grams of N still needs to be added. To get this, extra calcium or potassium nitrate can be added. Using different fertilisers to work out the nutrient mixture might also give a closer result. But in this situation, the solution could also be left a little short of nitrogen because such small nutrient variations do not affect plant growth or yield. Formulating hydroponic mixtures is all about balancing best-bet formulations that are seldom precisely correct.

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To add micronutrients Using equation 1 Iron, using iron chelate:

3 x 100 15.3

= 19.6 g Manganese, using manganese sulphate:

0.3 x 100 32.5

= 0.92 g Boron, using borax:

0.3 x 100 11.5

= 2.6 g Zinc, using zinc sulphate:

0.1 x 100 22.7

= 0.44 g Copper, using copper sulphate:

0.05 x 100 25.6

= 0.2 g Molybdenum, using sodium molybdate:

0.05 x 100 39.7

= 0.13 g 3.5. Diagnosing nutritional deficiencies The correct diagnosis of nutritional deficiencies is important in maintaining optimum plant growth. The recognition of these symptoms allows hydroponics growers to fine tune their application of nutrients, as well as minimize stress conditions. However, the symptoms expressed are often dependent on the species of plant grown, stage of growth, and other controlling factors. Therefore, growers should become familiar with nutritional deficiencies on a crop-by-crop basis. Record keeping and photographs are excellent tools for assisting in the diagnosis of nutrient deficiencies. Photographs allow growers to compare symptoms to previous situations in a

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step-by-step approach to problem solving. Accurate records help in establishing trends as well as responses to corrective treatments. Because plant symptoms can be very subjective it is important to approach diagnosis carefully. The following is a general guideline to follow in recognizing the response to nutrient deficiencies. Further guidance and advice on nutritional deficiencies should be sought from ADFSC’s extension specialists. Nitrogen Symptoms of nitrogen deficiency include restricted growth of tops and roots, and especially lateral shoots. Plants become spindly with general chlorosis of entire plants, to a light green and then a yellowing of older leaves which proceeds toward younger leaves. Older leaves defoliate early. Phosphorus Symptoms of phosphorus deficiency include restricted and spindly growth similar to that of nitrogen deficiency. Leaf color is usually dull dark green to bluish green, with purpling of petioles and the veins on underside of younger leaves. Younger leaves may be yellowish green with purple veins with N deficiency and darker green with P deficiency. Otherwise, N and P deficiencies are very much alike. Potassium Symptoms of potassium deficiency include older leaves showing interveinal chlorosis and marginal necrotic spots or scorching, which progresses inward and also upward toward younger leaves as deficiency becomes more severe. Typical potassium deficiency of fruit is characterized by color development disorders, including blotch ripening. Calcium Symptoms of calcium deficiency include slight chlorosis to brown or black scorching of new leaf tips and die-back of growing points. The scorched and die-back portion of tissue is very slow to dry so that it does not crumble easily. Boron deficiency also causes scorching of new leaf tips and die-back of growing points, but calcium deficiency does not promote the growth of lateral shoots and short internodes as with boron deficiency. Magnesium Symptoms of magnesium deficiency include interveinal chlorotic mottling or marbling of the older leaves which proceeds toward the younger leaves as the deficiency becomes more severe. The chlorotic interveinal yellow patches usually occur toward the center of the leaf with the margins being the last to turn yellow. In some crops, the interveinal yellow patches are followed by necrotic spots or patches and marginal scorching of the leaves. Sulphur Symptoms of sulphur deficiency resemble nitrogen deficiency in that older leaves become yellowish green and the stems become thin, hard, and woody. Some plants show colorful

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orange and red tints rather than yellowing. The stems, although hard and woody, increase in length but not in diameter. Iron Symptoms of iron deficiency start with interveinal chlorotic mottling of immature leaves and in severe cases the new leaves become completely lacking in chlorophyll but with little or no necrotic spots. The chlorotic mottling on immature leaves may start first near the bases of the leaflets so that in effect the middle of the leaf appears to have a yellow streak. Manganese Symptoms of manganese deficiency start with interveinal chlorotic mottling of immature leaves and, in many plants, it is indistinguishable from that of iron. On fruiting plants, the blossom buds often do not fully develop and turn yellow or abort. As the deficiency becomes more severe, the new growth becomes completely yellow but, in contrast to iron necrotic spots, usually appear in the interveinal tissue. Zinc Symptoms of zinc deficiency include interveinal chlorotic mottling on the older leaves, and in others it appears on the immature leaves. It eventually affects the growing points of all plants. The interveinal chlorotic mottling may be the same as that for iron and manganese except for the development of exceptionally small leaves. When zinc deficiency onset is sudden, such as the zinc left out of the nutrient solution, the chlorosis can appear identical to that of iron and manganese without the little leaf. Boron Symptoms of boron deficiency include slight chlorosis to brown or black scorching of new leaf tips and die-back of the growing points similar to calcium deficiency. Also the brown and black die-back tissue is very slow to dry so that it cannot be crumbled easily. Both the pith and epidermis of stems may be affected as exhibited by hollow stems to roughened and cracked stems. Boron deficiency can result in swollen miss-shaped fruit. Copper In copper deficiency, leaves at top of the plant wilt easily followed by chlorotic and necrotic areas in the leaves. Leaves on top half of plant may show unusual puckering with veinal chlorosis. Absences of a knot on the leaf where the petiole joins the main stem of the plant beginning about 10 or more leaves below the growing point. Molybdenum In molybedum deficiency, older leaves show interveinal chlorotic blotches, become cupped and thickened. Chlorosis continues upward to younger leaves as deficiency progresses. 3.6. Sampling nutrient solutions When collecting a sample from the nutrient solution:

Collect samples from the plant environment, particularly the root zone.

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Substrate (growing media) samples should be taken from all levels of the container.

If any areas of the plant show symptoms of nutrient deficiency or imbalance, measure the nutrient concentration of the solution in the affected area and compare with that of a healthy plant.

To collect samples from substrates follow the procedure: ‒ add twice the volume of distilled water ‒ stir the mixture and leave it 15 minutes ‒ collect the water through filtration paper, then measure EC and pH

3.7. Calibrating pH meters This information refers to handheld meters used to check pH in the growing media, solution, and other locations, not the pH sensor that is part of the main fertigation system. Select pH meters with an accuracy of ±0.1 pH unit and range of 1-14 as they can be used for fertiliser injector calibration as well as the substrate and solution testing. pH meters should normally be replaced each year. 3.7.1. Why pH meters need to be calibrated pH meters need to be calibrated so they give the correct measurements, standard pH solutions with a known pH are used to calibrate the pH meter. pH meters do not stay set correctly, so may give incorrect readings leading to incorrect decisions, and subsequent poor crop management. This can mean lower yields and poorer quality crops. 3.7.2. How often do pH meters need to be calibrated pH meters need to be calibrated regularly. The instructions that come with the meter will say how often. pH meters should be calibrated on a routine basis, ideally every week. 3.7.3. Before starting the calibration

Check the batteries.

If the meter has not been used for a long time, place the probe in tap water for about five minutes before calibrating.

Put the probe in the calibration solution then turn it on.

Wait for reading to stop changing, his may take up to 30 seconds. 3.7.4. How to calibrate a pH meter

1. There are two normal standard pH solutions. One solution has a pH of 4.0 and the other solution has a pH of 7.0. Make sure that the standard pH solutions (also called calibrating fluids) are fresh.

2. A typical pH meter has two adjustment screws. A pH meter must be adjusted to two values. Some meters have automatic calibration.

3. Pour a small volume of the first standard solution into a small container. 4. Put the probe of the pH meter into the standard solution with a pH value of 7.0.

Then, turn the first adjustment screw until the meter reads the value of the standard solution.

5. Rinse the probe well in clean water and dry using tissue paper. 6. Then pour a small volume of the second standard solution into another small

container.

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7. Now, put the probe of the pH meter into the standard solution with a pH value of 4.0. Turn the second adjustment screw until the meter reads the value of the standard solution.

8. The pH meter is now calibrated. 9. Throw out the used standard solutions. Never put used solution back into the bottle. 10. When not in use, the pH meter probe must be kept wet. Some types of pH probes

can be stored in a container of tap water. Otherwise, a special fluid will be supplied by the manufacturer of the pH meter.

3.8. Calibrating EC meters This information refers to handheld meters used to check EC in the growing media, solution, and other locations, not the pH sensor that is part of the main fertigation system. EC meters need to be calibrated so that they give the correct measurements. EC meters do not stay set correctly, so incorrect decisions could be made if EC meters are not properly calibrated. This can mean lower yields and poorer quality crops. EC meters should normally be replaced each year. EC meters need to be calibrated regularly. The instructions that come with the meter will say how often. EC meters should be calibrated on a routine basis, ideally every week. 3.8.1. Before starting the calibration

Check the batteries.

If the meter has not been used for a long time, place the probe in tap water for about five minutes before calibrating.

Put the probe in the calibration solution then turn it on.

Wait for the reading to stop changing. This may take up to 30 seconds. 3.8.2. How to calibrate an EC meter

1. The normal standard EC solution used to calibrate an EC meter is potassium chloride (KCl). The most commonly used solutions are either 1.413 mS/cm or 2.76 mS/cm. Make sure that the standard EC solution (also called calibrating fluid) is fresh.

2. On most EC meters, calibration is done with an adjustment screw or knob. 3. Pour a small volume of the standard solution into a small container like a plastic film

container. 4. Put the probe of the EC meter into the standard solution. Then turn the adjustment

screw until the meter reads the value of the standard solution. 5. The EC meter is now calibrated. 6. Throw out the used standard solution. Never put the used solution back into the

bottle. 3.9. Measuring distribution uniformity of irrigation 3.9.1. What is distribution uniformity and why is it important? Distribution uniformity is a way of measuring whether all plants are getting the same amount of water. It is measured as a percentage (DU %). The higher the distribution uniformity, the better the irrigation system is working. The amount of water that comes out of an emitter in the hydroponic system may be different to the amount coming out of

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another emitter. To make sure that crop grows evenly, every plant has to get the right amount of water. If one section of the greenhouse gets more water than another section during irrigation, some plants will either get too much or not enough water and nutrients. This will reduce yield, and can also make pest or disease problems worse. For a hydroponic system, the distribution uniformity (DU %) should be 95-100%. 3.9.2 How to improve distribution uniformity The following actions can be taken to improve DU:

1. Flush hoses and laterals once a week. 2. Flush sub and main irrigation lines every month. 3. Keep filters clean, make sure they are in good condition. 4. Use cleaning agents (such as an acid flush) to remove bacterial and mineral

blockages. 5. Avoid high and low areas in the hydroponic system. 6. Control the water pressure between emitters. 7. Make sure the pumping capacity of the pump is correct for the size of the irrigation

section. 3.9.3 How to calculate distribution uniformity To check if the hydroponic system is working properly:

1. Work out the average water application rate for all the sampled emitters 2. Work out the average water application rate for the lowest 25% of the sampled

emitters 3. Calculate the distribution uniformity (DU %)

Each section of the hydroponic system needs to be checked separately. Samples of water are collected from different areas of the hydroponic system. If there are any parts or areas of the hydroponic system where there may be a problem, take extra samples. Take at least 28 samples from each area tested. 3.9.4. Average water application rate The application rate is the amount of water (in litres) that each emitter puts out in one hour.

1. Choose the locations to be sampled. Four emitters should be selected from each lateral pipe. One sample needs to be taken from an emitter near the beginning of the lateral pipe and one sample from an emitter near the end of the lateral. The other two samples should be from emitters somewhere along the row, for example, one third and two thirds of the distance along the row. If there are 7 rows in the greenhouse, 28 samples will be collected.

2. Place a cup or small container under each emitter that is sampled. 3. Turn on the irrigation system for 60 seconds (1 minute) then turn off the water. 4. Collect each sample and use a measuring cylinder to measure the amount of water

(in millilitres, ml) in the cup. Record the amount of water for each emitter on a data sheet.

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5. Calculate the amount of water that comes out of each emitter in millimetres per hour (L/hr). Amount of water per hour (L/hr) = Water collected (ml) x 60. Record these numbers on a data sheet.

6. Add up the numbers for all the emitters. Divide this total volume by the number of emitters sampled.

7. Record this number on the data sheet. 3.9.5. Average water application rate for the lowest 25% of emitters

1. Rank the emitters in order of how much water they put out. 2. Mark which ones make up the lowest quarter (25%) of emitters. 3. Add up the numbers for the lowest 25% of the emitters. 4. Divide this total volume by the number of emitters (lowest 25%). 5. Record this number on the data sheet.

3.9.6. Calculate the distribution uniformity percentage (DU%)

1. Divide the average application rate of the lowest 25% of the emitters by the average application rate of all the emitters.

2. Multiply this number by 100.

Average application rate of lowest 25% of sampled emitters DU% = x 100 Average application rate of all sampled emitters 3.10. Measuring run off volume of irrigation 3.10.1. What is run-off volume? The run-off volume is the amount of water that drains away from the crop over a period of time, for example, each day. The run-off volume is related to the amount and frequency of irrigation. It is worked out as a percentage (%) of the amount of water given to the plant over the same period of time (irrigation volume). 3.10.2. Why measure run-off volume? Run-off volume is measured because it can affect the root zone solution and is an important tool to manage root zone EC and root zone pH. By measuring the run-off volume, it is then possible to compare it with a target run-off volume. 3.10.3. What is a target run-off volume? A target run-off volume percentage can be used to guide irrigation and crop management decisions. Often a daily target is used. Sometimes targets can be set for different parts of the day such as morning, middle and afternoon. Commonly used target volumes are around 10% though may be up to 30% (or even higher in some situations). 3.10.4. How is run-off volume collected? Run-off needs to be collected from one or more plants in the greenhouse for each separate irrigation section. An irrigation section is a group of plants which are all irrigated at the same

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time with the same nutrient solution. A collection tray needs to be set up to collect drainage water from the sample plant. 3.10.5 How is the irrigation volume collected? The irrigation volume needs to be collected from one or more drippers in the greenhouse from the same irrigation section that the run-off volume is being collected. Put a spare dripper into a collection container. The volume of water in this container will be a measure of the amount of water each plant is getting. Note that if the number of drippers used for the irrigation volume is different to the number of drippers from which the run-off volume is collected, the calculations need to be adjusted. 3.10.6. How to measure run-off volume? The amount of water that drains from the plant during the day (or other period of time) is measured in millilitres. This is then recorded as a percentage (%) of the amount of water that is irrigated to the plant (irrigation volume) over the same period of time. Always empty the container after recording the volume. For example Assume 1000 ml of water comes out of the dripper in a day and is collected in the irrigation volume container. Assume also that 150 ml of water drains out of the plant bag and is collected in the run-off volume container over the same period of time. Run-off volume % = 150 x 100

1000 = 15% In this example, the run-off volume is 15%. This means that 15% of the water that is given to the plants, drains away from the plants. 3.10.7. How to make use of the run-off volume? The run-off volume has an impact on the root zone EC, root zone pH as well as crop balance. These are important factors that must be carefully managed to make the crop produce an optimal yield and stay healthy. By adjusting irrigation so that the run-off volume is more or less or the same as the target volume, it is possible to manage the plant to make it more vegetative or more generative, also to keep the plant well balanced. 3.11. Hydroponics system hygiene To ensure the effective use of the fertigation system, the following steps should be taken:

1. Treat system at regular intervals by injecting chlorine or acid, to avoid buildup of contaminants such as bacteria and algae.

2. Chlorine injection must never be done while fertigation is taking place as chlorine may interfere with nutrient availability to plants.

3. Care should be taken when injecting acid through the system, as acidic solutions can damage irrigation system hardware.

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4. Corrosion-resistant fittings should be used if acids are injected. 5. Special care should be taken when phosphoric acid is injected into irrigation water

as it may precipitate out with the calcium in the solution. 6. Following irrigation water acidification, the system should be flushed for half an

hour to ensure the injected acid is flushed out of the system. 7. Ensure irrigation system has been flushed out before commencing fertigation 8. Check fertiliser compatibilities before starting fertigation 9. Ensure injection point is upstream of filter system so that any undissolved fertiliser

or precipitants can be removed by the filter. 10. Ensure the time needed to distribute the fertiliser is less than that needed to supply

enough water to the whole greenhouse area that is being fertigated. 11. Overwatering will cause leaching of fertiliser away from the root zone.

The following should be monitored at regular intervals during a fertigation program:

1. Substrate temperature effects on nutrient availability in the root zone 2. pH effects over time in the root zone 3. Blockages and corrosion of irrigation outlets and other components 4. Reaction of nutrients with dissolved salts in water or soil

The crop production system should be cleaned out and thoroughly sanitized between crop cycles. 3.12. Checklist for adopting good agricultural practices in hydroponics The following checklist of 10 priorities can be used to determine the extent of Good Agricultural Practices being used, and to make improvements for the future. 3.12.1. Is the DRAIN EC checked and recorded each day? Electrical conductivity (EC) is used to describe the strength of the nutrient solution. It is a measure of total strength not of specific nutrients. The most important part of nutrient management is that the nutrient solution around the roots must be managed – the root zone solution. The easiest way is to measure and record the EC of the run-off. This is called the DRAIN EC. Run-off needs to be collected from one or more plants in the greenhouse. Nutrient management decisions should be based on the drain EC. 3.12.2. Is the DRAIN pH checked and recorded each day? The pH is a measure of how acid or alkali the nutrient solution is. It is measured on a scale of 0 – 14. The pH of the nutrient solution around the roots is what matters – the root zone solution. The easiest way is to measure and record the pH of the run-off. This is called the DRAIN pH. Run-off needs to be collected from one or more plants in the greenhouse. Management of pH should be based on the drain pH. 3.12.3. Is the run-off volume collected, measured and recorded each day? The volume of run-off is related to the amount and frequency of irrigation. It can affect the root zone solution and is a valuable tool to manage root zone EC and pH. Run-off needs to be collected from one or more plants in the greenhouse. A daily target volume (e.g. between 10% and 30%) is used to plan irrigation frequency and amount.

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3.12.4. Is a balanced nutrient solution being used? A well balanced nutrient solution is necessary to grow a healthy profitable crop. The nutrient solution needs to be (1) balanced, (2) suitable to the crop and growing conditions, and (3) adjusted to the quality of your water. Adding individual fertilisers to a nutrient solution to address a problem without balancing the whole formula can make bigger problems and be more expensive. Most formulations are within the following ranges: N 150 – 250ppm; P 25 – 50ppm; K 100 – 300ppm; Ca 150 – 200ppm; S 30 – 300ppm; Mg 25 – 45ppm; Fe 2 – 3ppm; Mn 0.3 – 0.5ppm; Zn 0.2 – 0.5ppm; B 0.2 – 0.4ppm; Cu 0.05 – 0.3ppm; Mo 0.01 – 0.05ppm. 3.12.5. Is the irrigation distribution uniformity checked regularly? One of the most important areas of irrigation is uniformity. Irrigation distribution uniformity (DU %) refers to how well water is distributed through the system. A high uniformity will give: (1) more control over the crop, (2) a healthier more productive crop, and (3) more efficient water use. A DU% of 90 – 100% is excellent. If the DU% is less than 70%, the irrigation system needs to be fixed. 3.12.6. Does the substrate provide both adequate air and water for the crop? The performance of the crop is affected by the substrate being used. A hydroponic substrate needs to be uniform. The water holding capacity (WHC) and the air filled porosity (AFP) affect the way that the crop needs to be irrigated. As a substrate ages, these properties will change. A hydroponic substrate needs to have a total porosity of around 60 – 70% of total volume. The AFP needs to be at least 10%, but can be up to 30%. The WHC needs to be around 30 – 60% of total volume. 3.12.7. Is the water free from pathogens and of good quality? In hydroponics it is very important that the water being used is free from plant pathogens. Any water that has been in contact with soil needs to be treated before being used. Run-off water also needs to be treated to kill pathogens before being used again. Water also needs to be of good quality, ideally: Chloride < 70ppm; Sodium < 60ppm; bicarbonate < 60ppm; iron < 1.5ppm; Copper < 2ppm; Zinc < 1.5ppm; Boron < 2ppm. 3.12.8. Can nutrient disorders in the crop be identified? Making the correct identification of a nutrient disorder is critical to deciding on the right control and on-going management action. If nutrient disorders cannot be identified correctly, there is a risk of wasting money by using a spray or other control strategy that does not work. There is also a risk of making the problem worse or creating a new problem. 3.12.9. Is plant balance considered when making nutrient solution decisions?

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To grow a profitable crop, it is important to be in charge of what the crop is doing. The root zone nutrient solution is an important tool in managing plant balance. 3.12.10. Is the waste water managed properly? It is very important to properly manage the wastewater from the hydroponics system. There are several options. The best option is to collect, treat and reuse the water. This saves fertiliser, water and money. If not reusing the run-off nutrient solution, it is important that is managed properly. The water needs to be drained away from the cropping area and contained, such as in a tank.

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4. Appendices 4.1. Greenhouse structures and specifications Greenhouse structures should provide the required growing conditions for plants, by optimizing the influence of external environmental factors such as temperature, sunlight, and wind. The external and internal structure of the greenhouse should be robust, safe, constructed using appropriate technology and materials, and it should comply with building regulations. It should be durable and easy to maintain. It should be designed to last for at least 20 years. Greenhouses are a technology based investment. The higher the level of technology used, the greater potential for achieving tightly controlled growing conditions. This capacity to tightly control the conditions in which the crop is grown is strongly related to the health and productivity of the crop. 4.1.1. Multi-span structures Multi-span greenhouses have a surface area smaller than a number of single span greenhouses of equivalent production capacity. This results in more effective climate control and significant energy savings. Substantial economies of scale and production efficiencies are also attainable using multi-span designs. Multi-spans are typically more robust in design. 4.1.2. Other types of structures Shade houses Shade houses are structures which are covered in woven or otherwise constructed materials to allow sunlight, moisture and air to pass through the gaps. The covering material is used to provide a particular environmental modification, such as reduced light or protection from severe weather conditions. The height of the structure will vary according to the type of crop being produced. Shade houses are used over outdoor hydroponic systems, particularly in warmer regions. Screen houses Screen houses are structures which are covered in insect screening material instead of plastic or glass. They provide environmental modification and protection from severe weather conditions as well as exclusion of pests. They are often used to get some of the benefits of greenhouses in hot or tropical climates. Crop top structures A crop top is a structure with a roof but which does not have walls. The roof covering may be a greenhouse covering material such as plastic or glass, or shade cloth or insect screening. These structures provide some modification of the growing environment such as protection of the crop from rain or reduction of light levels. 4.1.3. Low technology greenhouses

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Tunnel houses, or "igloos", are the most common type. They do not have vertical walls, and have. They have poor ventilation. This type of structure is relatively inexpensive and easy to erect. But production potential is still limited by the growing environment and crop management is relatively difficult. Low level greenhouses generally result in a suboptimal growing environment which restricts yields and does little to reduce the incidence of pests and diseases. 4.1.4. Medium technology greenhouses Medium level greenhouses are typically characterized by vertical walls. They may have roof or side wall ventilation or both. They are usually clad with either single or double skin plastic film or glass and use varying degrees of automation. Medium level greenhouses offer a compromise between cost and productivity, with production often more efficient than field production. They offer greater opportunity to use non-chemical pest and disease management strategies, but overall the full potential of greenhouse production is difficult to achieve. 4.1.5. High technology greenhouses High level greenhouses have a wall height of at least 4 meters, with the roof peak being up to 8 meters above ground level. These structures offer superior crop and environmental performance. High technology structures will have roof ventilation and may also have side wall vents. Cladding may be plastic film (single or double), polycarbonate sheeting or glass. Environmental controls are almost always automated. These structures offer significant opportunities for economic and environmental sustainability. Use of pesticides can be significantly reduced. Although these greenhouses are capital intensive, they offer a highly productive, environmentally sustainable opportunity for an advanced fresh produce industry. Investment decisions should, wherever possible, look to install high technology greenhouses for hydroponic production systems. 4.1.6. Greenhouse cooling systems Greenhouses operating in UAE, in very hot and humid conditions during the summer, require cooling systems for optimum plant growth and improved worker efficiency. Generally an evaporative cooling system, comprising of fans and cooling pads, is used to lower air temperatures. Evaporative cooling uses the natural relationship between relative humidity, water, and air temperature. When water is evaporated it has a cooling effect. Humidity is also increased and the vapor pressure deficit is reduced. Air temperature can be measured as either dry or wet bulb temperature. The wet bulb temperature gives an indication of what temperature air can be cooled to with evaporative cooling. The amount of cooling that can be achieved from evaporative cooling systems is dependent on how much water can be evaporated, so is related the amount of water already in the air, the relative humidity. In the fan and pad systems, an exhaust fan is located at one end of the greenhouse, and a porous pad is built into the wall of the structure at the opposite end. A pump circulates water over and through the pad. When the fan is in operation, it pulls air from outside the structure, through the evaporative pad, into the greenhouse. The air, passing through and over the wet pad evaporates some of the water and is cooled. As a result, cool air is drawn into the greenhouse to replace the hot air expelled by the fan.

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These systems are quite effective for cooling but are relatively expensive to install and maintain. A disadvantage of the fan and pad system is that it tends to create a significant temperature gradient from one end of the greenhouse to the other (warmest at the fan end and coolest at the pad end) which can affect crop uniformity and make management more difficult. Under extreme conditions which demand a lot of cooling, the air movement through the greenhouse generated by exhaust fans may damage some plants. Under high summer temperatures (40OC and above) and low relative humidity (around 30%) the consumption of cooling water using this system will be around 6 m3 per hour. The level of water consumption depends on the levels of temperature and humidity in the outside air. In UAE, during the hot summer months, it is important to keep the fresh water supply to the pads running constantly to compensate for the water loss from the pads by evaporations. To prevent the build-up salts on the pad surface, which will results in pressure drop within the systems, some of the recirculated water must be discharged, and replaced by fresh water at regular intervals. 4.1.7. Greenhouse shading Shading is used to control light and lower interior temperatures by blocking out unwanted levels of solar radiation. Shades can be coupled with shade moving devices to provide movable curtains that offer some amount of control of the greenhouse temperature. The shade should be mounted on the exterior side of the greenhouse for the greatest reduction in the heat load, although inside shading can also be used. 4.1.8. Greenhouse monitoring systems It is very important to monitor the growing conditions within the greenhouse. The right information is needed to make correct decisions about the crop. Temperature and relative humidity (and/or vapor pressure deficit) need to be continuously monitored. Light levels should be checked at least periodically to make sure covering materials are performing adequately. As described in Section 3, the electrical conductivity and pH of both the feed and drain solutions should be regularly monitored in every hydroponic system. Temperature and relative humidity sensors should be placed level with the growing tip of the crop. Placing a thermometer near the door of a greenhouse might be convenient but it will not give the information needed for producing an optimal crop. Medium and high technology greenhouses make use of a range of sensors which link into automated control systems. These systems can monitor temperature, relative humidity, vapor pressure deficit, light intensity, electrical conductivity (feed and drain), pH (feed and drain), carbon dioxide concentrations, wind speed and direction and even whether or not it is raining. The information is used to control cooling, venting, fans, screens, nutrient dosing, and irrigation. Correct operation of the automatic controllers is essential to management of an optimal growing environment. Emergency alarms and backup generators may be used in case of problems or power failure due. 4.1.9. Greenhouse specifications

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The following specifications are recommended for a typical, start up 2,000 m2 greenhouse facility for hydroponics production in UAE. Greenhouse dimensions

Number of spans = 8

Span dimensions = 32.5 x 8 m

Height under gutter = 4.0 m

Height above gutter = 5.7 m

Distance between posts = 2.5 m Greenhouse accessibility

Greenhouse front door = 1

Greenhouse side door = 1

Buffer room door = 1

Dimensions of doors = W - 2m, L - 2m, H - 2.25m

Opening/closing = sliding Greenhouse main structure

Posts = hot deep galvanized steel pipes, 2.5 inch - 1.8 mm

Basements = 40 x 40 with 70 cm depth

Arches = galvanized steel pipes, 2 inch - 1.7 mm

Structures = galvanized steel pipes,1.0 inch - 1.5 mm

Rain water collection gutters - thickness (high resistance) = 1.5 mm - width = 500 mm - height = 115 mm - top width = 345 mm - top height = 119 mm

Crop bars - round galvanized tube = 1.0 inch - 1.5 mm - vertical reinforced galvanized steel = 1.0 inch - 1.5 mm . - purling galvanized steel pipes = 1.0 inch - 1.5 mm

Side cladding = polycarbonate (UV treated), 6mm thick, European standard

Crop load = 40kg/m2 (150 N/m2)

Wind load = 120km/hr A concrete frame will be built around the structure to fix the polycarbonate and fix the external posts together. Greenhouse cover materials

Cover material = plastic film UV treated (3 years warranty), 200 micron Greenhouse fans

Two main exhaust fans = 1.5HP (138 x 138cm) 46,500 m3/h

One extra exhaust fan in each span, at front gable to extract hot air from arch area

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Exhaust fans = 0.5HP (75 x 75cm) 10,600 m3/h

Air circulation fans (one fan per span) = 0.5 HP, round 62cm diameter Greenhouse cooling pads

CELdek European, US, Canada or Australia = 300 x 60 x 20 cm thickness Made of fluted cellulose sheets glued together, chemically impregnated with special compounds, with

- high cooling efficiency - high face velocity - self-cleaning design - low pressure drop leading to high fan performance - simple to maintain

Temperature and humidity controller

Thermostat x 3

Water recirculation system

Pumps = European, US, Canada or Australian

Pipes = PVC.

Water tank = fiberglass Frame All parts made from galvanized steel sheets 1.5 mm thickness, including the pad fixing belts and the gutters under the pads that are used to collect excess water. Electrical installations

Each zone supplied with its own power panel that receives its control signals from temperature and humidity thermostats.

The power panels include main switches for the fans and pumps with a selector switch with three positions (auto, manual, off)

All necessary protection boxes with switcher circuit breakers, relays, and wire terminals are supplied for each fan and each pump.

Electrical requirements

To allow for future expansion, a capacity of 200 kilowatts is recommended for a 2,000 m2 greenhouse hydroponics facility.

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4.2. Greenhouse covers Greenhouse covering materials can influence:

The productivity and performance of the greenhouse structure

The level and quality of light available to the crop The key characteristics that should be considered in selecting a covering material are:

1. Cost 2. Durability (how long it last) 3. Weight 4. Ease of repair or replacement, 5. How much light is transmitted through the material 6. How much energy moves through the material

In general, diffused light is better for plant growth than direct light. Diffusing materials are designed to scatter incoming light and result in better light conditions for crops, for example, a cloudy white plastic film diffuses light better than a clear plastic film. Fluorescent and pigmented films can increase the proportion of good red light. Greenhouse coverings all reduce light availability to some extent although light colour materials in the greenhouse, such as white weed matting, will increase the light available to the crop. Dust, attracted to plastic films, will reduce the transmission of radiation. Water droplets on the inside of coverings will reduce light transmission and block thermal radiation. The range of cover materials used in UAE are:

1. Glass 2. Plastic 3. Shade material

‒ net shade ‒ shade cloth ‒ white wash ‒ solar and thermal screens

4. Insect-proof screens 4.2.1. Glass Glass has long been a traditional covering for greenhouses worldwide, its favorable properties include:

1. High transmission in the photosynthetically active radiation (PAR) bandwidth 2. Good heat retention at night 3. Low transmission of UV light 4. Durability 5. Low maintenance costs

4.2.2. Plastic Sheeting These include:

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1. Polycarbonate 2. Acrylic (polymethyl methacrylate) 3. Fibreglass

Sheeting products are more durable than plastic films and have fairly good heat retention, good initial transmission in the PAR range, and low UV light transmission. 4.2.3. Plastic films Plastic films are the most suitable and the lowest cost type of covering material used in UAE. The types of film available are:

1. Polythene (polyethylene) 2. EVA (ethyl vinyl acetate) 3. PVC (poly vinyl chloride)

Coverings can have a variety of additives, used for improved performance. For example, films may be used to exclude ultra violet (UV) light, or to reflect long wave infra-red (IR) radiation to improve heat retention at night. Additives to the plastic can influence:

1. Durability 2. Capacity to reduce heat loss 3. Capacity to reduce droplet formation 4. Transmission of particular wavelengths of light 5. Capacity to reduce the amount of dust sticking to the film

4.2.4. Types of Additives

1. UV (290-400 nm) absorbers and stabilizers increase durability, reduce the potential damage to biological systems in the greenhouse and may control some plant pathogens.

2. Infrared (700-2500 nm) absorbers reduce long wave radiation and minimize heat loss.

3. Long wave radiation (2500-40000 nm) absorbers reduce the loss of heat radiated from materials and objects (including plants) inside the greenhouse.

4. Light diffusers scatter light entering the greenhouse, reducing the risk of plants getting burnt and improving the amount of light available to the lower parts of the plant.

5. Surfactants reduce the surface tension of water, dispersing condensation. 6. Antistatic agents reduce the tendency of dust to accumulate on plastic films.

In addition:

1. Colour pigments may improve plant growth by altering the proportion of selected wavelength ranges.

2. Fluorescence may be used to increase the emission of red light. 3. Glossy surfaces may repel insects.

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The process of making multilayer films enables thin layers of materials with different properties to be joined to make superior composite films. Properties such as durability, creep (deformation over time), and long wave radiation absorption can be improved. 4.2.5. Maintenance A poorly maintained covering material can lose a lot of energy and significantly increase production costs. Plastic coverings need to be replaced routinely. The performance of plastic coverings declines over time. Old coverings reduce light transmission which can restrict yield. The useful life of plastic films depends on the specifications of the plastic purchased. All plastic covering materials need to be replaced before they visibly start to break down. 4.2.6. Screens and netting Screens and netting can be used to reduce the amount of light or solar energy entering the greenhouse, to regulate the temperatures inside greenhouses and to protect plants from insects, pests and disease. Shading is commonly used in the UAE. It is available in the following forms: Shade cloth

Reduces the amount of solar energy entering the greenhouse.

Solar radiation can be decreased by 30% - 60% depending on the specifications of the shade cloth used.

Especially useful to reduce internal temperatures for greenhouse vegetable production.

Whitewash paints

Reduces the amount of radiation entering the greenhouse.

Reduces greenhouse internal temperature. Solar and thermal screens

Reduces the amount of solar radiation incident on the crop.

Prevents the escape of long wave radiation from the greenhouse, trapping warmth that maintains nighttime temperatures.

Thermal screens are typically removable so they are only drawn over the crop or structure when needed.

Insect-proof screens

Provides a physical barrier that excludes and reduces insect pests.

The main disadvantage is that they restrict airflow.

Screens are available specifically in different sizes to target different insects.

Thrips require the finest sized screen, whitefly require a standard gauge screen.

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4.3. Hydroponic system specifications The following specifications are recommended for a typical, startup 2,000 m2 greenhouse hydroponics production facility in UAE. Growing system

To accommodate 4,800 plants

Minimum 5 m3/hour irrigation capacity

Capacity for >22 schedule irrigation times per day, 5 min each

Automatic management of irrigation program with four starting conditions

Accurate measurement and correction of EC and PH.

Four fertiliser recipes from A, B, acid, base tanks.

Use of white color weed mat, chemical resistance grade, with five years warranty.

Use of upper shading system, 50 % shade

Main power supply and protection and main cable to the technical room Dosing unit

Minimum capacity = 5 m3

With 2 sets A, B, and C, and mixing tank system

Number of dosing channels to provide 2 mixes ‒ 4 x dosing channels for fertiliser on EC value ‒ 1 x dosing channel for acid/base on pH value ‒ 4 x dosing channels for fertiliser ‒ with Venturi and electrical quick action valves

Dosing capacity per channel = 30-300 litres/hr of fertiliser/acid solution at 3.0 Bar

Pump capacity net = min 5 m3/hr

Mains voltage pump = 3 phase

EC measurement = 1 EC sensors with thermistor element, 3kW/25°C for temperature compensation of the EC-value

pH measurement = 1 pH electrodes max. 10 bar, high pressure with coaxial cable 3 meters

Electrical cabinet = manual switch, motor starter and thermal protection for pump

Dosing software

Valve group = 4

Starting program with starting conditions = 4

Irrigation main line = 1

Water system with control of 2 irrigation pumps = 1

Liter counter measurement = 1

EC/pH measurement and control without dosing channels = 1

Control of dosing channel for dosing valve = 3

Water treatment recipe = 4 Light intensity sensor with the irrigation controller = 1

Configuration

Water system = 1

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Liter counter measurement = 1

EC/pH measurement and control = 2

Dosing channel control for dosing valve = 6

Water treatment recipe = 4

Irrigation valves = 60

Irrigation controller with light intensity capability Other specifications

Fresh water supply pump 5m3/h = 1

Solenoid valves = 8

Drip irrigation line 16 mm, 30m long = 40

PC fully compensate non leak drippers with hydroponic stake, 2 litres/hr = 4,800

Irrigation tank ‒ 3,000 gals vertical tank PVC Insulated = 2 ‒ screen filter 2 inch on the fresh water line = 1 ‒ submersible pumps = 1 ‒ solution tanks A, B = 400 liter ‒ acid & base tanks = 200 liter ‒ screen filter 2 inch on the fresh water line = 1

Drain water collection installation ‒ 500 Gals drain tank horizontal = 2 ‒ submersible pump = 2 ‒ return line to untreated water tank = 2

Growing gutter, steel or PVC, 30m x 200 cm x 90cm, water channel 40mm = 40

Growing bags, coco peat or rock wool 100 x 20 x 16 = 1,200

Growing rock wool cubes = 4, 800

Pre filtration, sand filter auto back wash, 7-10 m3/h = 1

UV filter, low pressure mercury vapor lamps, wave length 254 nm, 250 mJ/cm2 = 1

Drainage tank 500 gallon = 1