Lettuce was cultivated in 4500 B.C. in the Mediterranean basin. Only in 1543 was the first know head lettuce produced in Europe. Lettuce was first cultivated for the edible oils that the leaves produce. Only later, in Egypt, was lettuce leaves eaten raw. There are four lettuce types cultivated for the fresh market, these are: [...]
Most automated systems installed in closed hydroponic systems use injectors rather than proportioners. A simplified diagram of where to install such a system is provided below. Many advanced injectors such as the Priva® and Volmatic® systems use much more complex configurations. Most of the systems use two pH probes and two EC probes in case [...]
Mechanical filtration is not an effective tool to prevent water borne diseases in NFT hydroponic nutrient solutions. It has been found that the total organic carbon content can reach 20 mg.L-1 for 2-3 months without affecting plant growth. There are many other compounds that attribute to the total carbon mass such as chelates and the [...]
The correct flow rate of closed hydroponic systems is critical for optimal growth of plants. The flow rates are important for all types of closed hydroponic systems such as pure NFT systems, gravel cultures and ebb-and-flow systems. Inadequate flow rate will result in: Reduced oxygen levels at root surfacesIncreased susceptibility of diseasePlants are under stress [...]
The pythium fungus is one of the serious diseases that growers can encounter in hydroponic systems. The disease can be kept at bay if the irrigation system can be closed of from the environment. The best method to control pythium and phytophtera is by maintaining a 2.5% concentration of hydrogen peroxide. It has been determined [...]
Nutrient removal is quite often neglected in closed hydroponic systems since it is difficult to measure and control. The reason is that not all nutrients are removed at an equal rate by plant roots. The essential nutrients can be grouped into 3 categories based on the rate of uptake from the nutrient solution. Elements are actively [...]
Refilling nutrient solutions are only required when a closed (NFT) system is used. With open hydroponic systems the nutrient solution is not re-used so no refill solution is required. Very little information is available on the subject and methods should be developed according to system design. Each system will have unique requirements because of factors such as: plant growth [...]
The irrigation water of hydroponic systems must be filtered to keep foreign objects out of the system. Open systems are relatively easy to filter since the water moves in one direction, so it is used only once. With closed systems the situation is entirely different. Not only is the water polluted with organic material from [...]
The correct gravel depth is important for the development of the roots system. Too shallow gravel will not only restrict root development and volume, but will also cause the development of algae on the surface of the gravel. The algae attract fungus gnats which feed on the roots of plants. The reason why the gravel [...]
The basis on which to choose a small nutrient tank or large nutrient tank will be: The relative volume circulating at any given time in the whole systemThe rate at which the solution formulation must be changedThe estimated risk that diseases can enter the system and how effectively it can be controlledCapital availableAmount of water [...]
Hydroponic nutrient tanks can be made from any type of material as long as it does not react or cause a reaction with the nutrient solution. For instance, galvanized tanks are not suitable if the nutrient solutions come in direct contact with the metal. If galvanized tanks are used, the plants will show a Zn [...]
Plastic gullies (or also called hydro-liners) are made from thick durable plastic with a thickness between 125 micron and 500 micron. The recommended thickness to use is the 500 micron plastic. Although it is much more expensive, it is also more durable especially during the building phase where people tend to walk over the plastic [...]
Over the years, closed hydroponic systems have been criticized quite often for their high initial capital cost and the perception that these systems have a high disease risk. During the initial development of the closed system in 1961, these criticisms might have been true since little scientific knowledge was available. Since 1961 an enormous amount [...]
