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

Transcription

1 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 4. Appendices 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 Measuring run off volume of irrigation Hydroponics system hygiene Checklist for adopting good agricultural practices in hydroponics 4.1. Greenhouse structures and specifications 4.2. Greenhouse covers 4.3. Hydroponic system specifications 1

2 Photographs [To incorporate into the document during publication] No. Section Description Got To get Ready Front cover and introduction: general pictures of hydroponics production 2 1 showing overall system, crops at different stages 3 1 within the system, final products Main components of hydroponics system: Water supply, desalination unit Fertigation system Substrate Greenhouse facilities Climate control system Power supply Details of fertigation system: Fresh water storage tanks Nutrient and chemical storage tanks Mixing tank ph meter EC meter Control system Irrigation system Pumps Waste water collection and recycling system Fresh water storage tanks Nutrient and chemical storage tanks Different injection systems: Suction injection Pressure differential injection Pump injection Different production systems: Water culture 2 photos showing the most relevant systems Substrate culture 4 photos showing the most relevant systems Common fertilisers used: Tank A 4 photos showing the most common fertilisers (container and/or bag and/or material) Tank B 4 photos showing the most common fertilisers (container and/or bag and/or material) Common acids and bases used: Acid container and/or bag and/or material of most common used 2

3 Base container and/or bag and/or material of most common used Common nutrient deficiencies: pictures showing the most common nutrient deficiencies Other information: Sampling nutrient solutions Calibrating ph meters Calibrating EC meters Measuring distribution uniformity Measuring run off volume Hydroponics system hygiene 4 pictures showing the most Important steps to take Greenhouse structures: Main components of greenhouse structure 4 pictures showing the most important parts Greenhouse cooling systems 2 pictures Greenhouse shading 4 pictures of main covers and shading options Back cover harvesting, final products, success stories 70 Harvesting of high value vegetables from hydroponics 71 production systems 4 pictures The ADFSC value chain and market 4 pictures Picture of successful hydroponics farmers (with text) from 77 2 demonstration farms in Western Region (Ali & Yafoor) 3

4 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. 4

5 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 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 5

6 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 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 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 (NO 3- ), the other is ammonium form (NH 4+ ). 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 6

7 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 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. 7

8 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 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 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. 8

9 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 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 Carbon dioxide Atmospheric carbon dioxide is required as the substrate for plants to convert to glucose through photosynthesis 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 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 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. 9

10 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 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. 10

11 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 Nutrient & chemical have a reliable supply of good quality water. The water must be storage tanks free of contaminants and have a maximum salinity level of Control 500 ppm unit (0.78 ds/m). The water storage tanks should hold A sufficient B water for???????? C D 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 ph & EC meters substances. Pumps Nutrient concentrates and chemical storage tanks Mixing tank The concentrated mixes of nutrients for the crop are stored Pumps & in the nutrient storage tanks. Nutrients are premixed into concentrated solutions according filters to recipes formulated to Water provide crops all their requirements for growth. These nutrients are mixed Irrigation with fresh system water treatment & to make the nutrient reuse solution that supplies the Recycling crops system 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 Water will clog irrigation pipes and Flow-through drippers. system Due treatment to the corrosive & nature of many fertilisers, tanks are usually made of polyethylene or fiberglass. disposal Where metal Fresh tanks are used, they should be either stainless steel or coated with an non-corrosive material water such tank as epoxy. Tanks should be large enough to hold the volume 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. 11

12 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 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 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 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. 12

13 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 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 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 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 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 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. 13

14 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 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 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. 14

15 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 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 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. 15

16 Figure 2. Different types of growth systems and support media Hydroponics production systems Water culture Substrate Nutrient film Deep flow Aeroponics Inorganic Organic Mixtures Perlite e Vermiculite Sawdust Peat moss Range of organic and inorganic mixtures Rockwool Reed/sedge peat Sand/gravel Coco peat Other s Other s 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. 16

17 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 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 ) 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. 17

18 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 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 18

19 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 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 liming is not required Other There are a range of other substrates that can be used for hydroponics, including mixtures of inorganic and organic media 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 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 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 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. 19

20 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 40 0 C) and low relative humidity (below 30%) the consumption of water for evaporative cooling will be around 6.5 m 3 per hour for an 8 m span greenhouse (approx. 300m 2 ). 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. 20

21 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 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. 21

22 Table 1. An evaluation of ph for soilless growing media Extremely low 4.5 or less Very low Low Slightly low Optimum Slightly high High Very high Extremely high 6.9 and higher Table 2. How to control ph in growing media To lower ph Add acid to the water (neutralizing of alkalinity), acidification Stop the use of basic fertilisers (e.g. calcium nitrate) and start the use of acidic fertilisers to lower ph In severe cases, drenching with aluminum sulphate or iron sulphate to rapidly lower ph To raise ph Stop adding acid to irrigation water Use basic fertilisers to raise substrate 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 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. 22

23 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) Excellent <0.25 <175 <20 <0.33 Boron (mg/l,ppm) Good Permissible Doubtful Unsuitable >3.0 >2100 >80 >1.25 Figure 3. Corrective measures for adjusting soluble salt and ph problems ph High Low Acid injection Leach Iron sulphate Base injection Dolomitic lime Calcium carbonate Hydrated lime Growing medium High More frequent irrigation Longer irrigation interval Soluble salts Low Less frequent irrigation Shorter irrigation intervals 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. 23

24 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 me/100g dry weight of material 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 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 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 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. 24