Hydroponics

Recirculating Vs. Nonrecirculating Systems

Hydroponic systems are categorized as open (Nonrecirculating), where after the nutrient solution has been delivered to the plant roots it is not reused; or closed (Recirculating) where surplus solution is recovered, replenished and recycled. Recirculating systems require a very different nutrient formulation and management system than nonrecirculating systems. Recirculating systems tend to start off with a well balanced nutrient formula that features plenty of each element for plant uptake. However, by the time the solution has passed through the root systems of the plants, certain nutrients may have been taken out more than others, causing imbalances in the nutrient solution that are unknown to the grower. As the EC is adjusted each day with more stock solution and additional water, some of the nutrients under heavy demand are replaced -- but sometimes not to sufficient levels. One example is potassium. In recirculating systems where some plants are carrying a heavy crop load, potassium can be depleted within a few days despite frequent additions of concentrated nutrient stock solutions.

In nonrecirculating systems, which are often seen as wasteful of nutrient solution since the excess runoff drains to waste, fresh nutrient solution is applied at each irrigation. Therefore, there is less of a chance that elements will be depleted over the long term (as long as a well-balanced nutrient formula is continually being applied). However, even in these systems, the nutrient needs to be monitored on a regular basis to determine plant nutrient uptake rates and to modify the nutrient formula. Some plants are extremely heavy feeders, particularly when carrying a heavy fruit load, and samples of runoff often show potassium and micronutrient depletion during certain crop stages.

Wick System

The Wick system is by far the simplest type of hydroponic system. This is a passive system, which means there are no moving parts. The nutrient solution is drawn into the growing medium from the reservoir with a wick. This system can use a variety of growing medium. Perlite, Vermiculite, Pro-Mix and Coconut Fiber are among the most popular. The biggest draw back of this system is that plants that are large or use large amounts of water may use up the nutrient solution faster than the wick(s) can supply it.

Water Culture

The water culture system is the simplest of all active hydroponic systems. The platform that holds the plants is usually made of Styrofoam and floats directly on the nutrient solution. An air pump supplies air to the air stone that bubbles the nutrient solution and supplies oxygen to the roots of the plants. Water culture is the system of choice for growing leaf lettuce, which are fast growing water loving plants, making them an ideal choice for this type of hydroponic system. Very few plants other than lettuce will do well in this type of system. This type of hydroponic system is great for the classroom and is popular with teachers. A very inexpensive system can be made out of an old aquarium or other water tight container. The biggest drawback of this kind of system is that it doesn't work well with large plants or with long-term plants.

Ebb And Flow (Flood And Drain)

The Ebb and Flow system works by temporarily flooding the grow tray with nutrient solution and then draining the solution back into the reservoir. This action is normally done with a submerged pump that is connected to a timer. When the timer turns the pump on nutrient solution is pumped into the grow tray. When the timer shuts the pump off the nutrient solution flows back into the reservoir. The Timer is set to come on several times a day, depending on the size and type of plants, temperature and humidity and the type of growing medium used. The Ebb and Flow is a versatile system that can be used with a variety of growing mediums. The entire grow tray can be filled with Grow Rocks, gravel or granular Rockwool. Many people like to use individual pots filled with growing medium, this makes it easier to move plants around or even move them in or out of the system. The main disadvantage of this type of system is that with some types of growing medium (Gravel, Growrocks, Perlite), there is a vulnerability to power outages as well as pump and timer failures. The roots can dry out quickly when the watering cycles are interrupted. This problem can be relieved somewhat by using growing media that retains more water (Rockwool, Vermiculite, coconut fiber.

Drip Systems

Recovery / Non-Recovery

Drip systems are probably the most widely used type of hydroponic system in the world. Operation is simple; a timer controls a submersed pump. The timer turns the pump on and nutrient solution is dripped onto the base of each plant by a small drip line. In a Recovery Drip System the excess nutrient solution that runs off is collected back in the reservoir for re-use. The Non-Recovery System does not collect the run off. A recovery system uses nutrient solution a bit more efficiently, as excess solution is reused, this also allows for the use of a more inexpensive timer because a recovery system doesn't require precise control of the watering cycles. The non-recovery system needs to have a more precise timer so that watering cycles can be adjusted to insure that the plants get enough nutrient solution and the runoff is kept to a minimum. The non-recovery system requires less maintenance due to the fact that the excess nutrient solution isn't recycled back into the reservoir, so the nutrient strength and pH of the reservoir will not vary. This means that you can fill the reservoir with pH adjusted nutrient solution and then forget it until you need to mix more. A recovery system can have large shifts in the pH and nutrient strength levels that require periodic checking and adjusting.

Aeroponics

The aeroponic system is probably the most high-tech type of hydroponic gardening. Like the N.F.T. system below the growing medium is primarily air. The roots hang in the air and are misted with nutrient solution. The mistings are usually done every few minutes. Because the roots are exposed to the air like the N.F.T. system, the roots will dry out rapidly if the misting cycles are interrupted. A timer controls the nutrient pump much like other types of hydroponic systems, except the aeroponic system needs a short cycle timer that runs the pump for a few seconds every couple of minutes.

N.F.T.(Nutrient Film Technique)

Of all the soilless methods, water culture, by definition, is a true hydroponic system. The nutrient film technique (NFT) is a relatively new water-culture system based on the simple principle of circulating a shallow stream, or film, of nutrient solution over the roots of growing plants to provide an adequate supply of water, nutrients, and oxygen. The concept of the nutrient film is credited to A. J. Cooper, who while at the Glasshouse Crops Research Institute in Littlehampton, England, recognized its value and called international attention to its commercial potential as early as 1973. Since then, NFT has undergone intensive testing by scientists and commercial growers in many countries, and is now considered a commercially viable form of water culture for several crops.

NFT has many advantages over other systems of crop production. It has been designed for simplicity, low cost, and dependability. In particular, it gives absolute control of the root environment; it greatly simplifies watering, and ensures a uniform nutrient supply across the whole crop. Root temperature can be raised or lowered easily whenever required merely by warming the nutrient solution or cooling of nutrient solution, which can be circulated either continuously or intermittently to further conserve energy and to control the growth of plants.

Other advantages include a rapid turnaround between successive crops, the potential for more efficient use of space because of the possibility of plant mobility, and the potential for more efficient use of water. NFT's high degree of control over nutrition, water availability, and root environment makes it the most sophisticated of all commercial plant-culture systems in practice today. Theoretically it offers the highest yield potential. However, many of the advantages of NFT are also offered, to some degree, by other soilless methods, notably rock wool. Much skepticism therefore persists about the future of NFT, because it is generally perceived as a technique that requires a high level of technical skill. Growers have some concern about the possibility that the recirculating nutrient solution may amplify and spread diseases in the system, resulting in disastrous crop losses. Unexplainable outbreaks of root death have repeatedly occurred, which have fueled concern over potential spread of diseases in NFT systems.

Future Of Hydroponics

Hydroponics is a relatively new technology, evolving rapidly since its inception 70 years ago. From its origins in acaemic research, to its utilization in industry and government, hydroponics has found many new applications. It is a versatile technology, appropriate for both developing countries and high-tech space stations. Hydroponic technology can efficiently generate food crops from barren desert sand and desalinated ocean water, in mountainous regions too steep to farm, on city rooftops and concrete schoolyards and in arctic communities. In highly populated tourist areas where skyrocketing land prices have driven out traditional agriculture, hydroponics can provide locally grown high-value specialty crops such as fresh salad greens, herbs and cut flowers.

Like manufacturing, agriculture tends to move toward higher-technology, more capital-intensive solutions to problems. Hydroponics is highly productive and suitable for automation. However, the future growth of controlled environment agriculture and hydroponics depends greatly on the development of systems of production that are cost-competitive with those of open field agriculture. Improvements in associated technologies such as artificial lighting and agricultural plastics, and new cultivars with better pest and disease resistance will increase crop yields and reduce unit costs of production. Cogeneration projects, where hydroponic greenhouses utilize waste heat from industry and power plants, are already a reality and could expand in the next few years. Geothermal heat could support large expanses of greenhouses in appropriate locations.

It has been proposed that glasshouses located in deserts of the world could one day serve a dual purpose, where antennas could be embedded into the glass to receive energy radiation from an array of energy collectors in space, while at the same time facilitate hydroponic production.

The economic prospects for controlled environmental agriculture and hydroponics may improve if governmental bodies determined that there are politically desirable effects of hydroponics that merit subsidy for the public good. Such beneficial effects may include the conservation of water in regions of scarcity or food production in hostile environments; governmental support for these reasons has occurred in the Middle East. Another desirable societal effect could be the provision of income-producing employment for chronically disadvantaged segments of the population entrapped in economically depressed regions; such employment produces tax revenues as well as personal incomes, reducing the impact on welfare rolls and improving the quality of life.

Hydroponics is a technical reality. Such production systems are producing horticultural crops where field-grown fresh vegetables and ornamentals are unavailable for much of the year. The development and use of controlled environment agriculture and hydroponics have enhanced the economic well being of many communities throughout the world.