Sustainable Farming - Types of Hydroponic Systems
Hydroponics is the method of growing plants without soil. Hydroponic systems deliver nutrients to the plant roots in a water-based solution rather than the plants extracting nutrients from the soil.
There are two main types of hydroponic systems – passive and active. Passive systems are the more basic of the two. These systems use a growing medium such as sand or vermiculite to retain moisture. They are ideal systems for beginners to use because they are easy to set up, portable, and inexpensive. The two types of passive systems are wick and drain-down.
Active systems are more complex, requiring a pump and other devices to administer the nutrient-rich solution to the plant. Some active systems also require a growing medium, though they use one that drains quickly like smooth gravel. Active systems include water culture, nutrient film technique (NFT), ebb & flow, recovery and non-recovery drip systems, and aeroponics.
Passive Hydroponic Systems
The wick system is the most popular of the passive systems, largely because of its simplicity. In a wick system, plants are placed in growing medium in a grow tray. Below the grow tray a reservoir holds the nutrient solution. Wicks stretch down to the solution and draws it up into the growing medium. The wick system is ideal for starting seeds or rooting cuttings. However, it does not support mature plants very well because of the limited room for roots to grow.
The drain down system is not as popular as the wick system because it requires more maintenance. In this system, plants are placed in a grow tray over a reservoir much like a wick system. The solution is poured through the system one to three times daily. It drains into the reservoir and can be re-used. Besides high maintenance, the main disadvantage of this system is that the roots can clog the drain channels.
Active Hydroponic Systems
Of the active systems, the water culture system is the simplest. Also called a sub-aeration system, it utilizes a foam platform that holds the plants. The platform floats directly on the nutrient solution. An air pump connected to an airstone oxygenates the solution and the plant roots. This system is found in classroom and is popular for growing leaf lettuce because lettuce is a water-loving plant which grows very well in this kind of setup.
The Nutrient Film Technique system is a classic hydroponic system. Plants are held in baskets with their roots dangling into a grow tray. Beneath the grow tray, a reservoir holds the nutrient solution which is pumped by a submersible pump into the grow tray using a tube. The solution flows over the roots and drains back to the reservoir. There is little maintenance because the pump continuously pushes the solution to the plant roots and there is no growing medium to replace. The biggest disadvantage of this system is root dieback from lack of oxygen in the solution. The system can, however, support large-scale crops and is a good choice for use in areas with poor soil quality.
The Ebb & Flow system is the most popular of the active systems because of its low maintenance. In this system, grow medium such as grow rocks or gravel fills the grow tray. The tray is placed over the reservoir which has a submerged pump in it set on a timer. When the timer turns the pump on, nutrient solution is pumped into the grow tray usually filling it. The timer turns the pump off and the solution drains out of the grow tray into the reservoir. The roots are oxygenated each time the grow tray is emptied of solution.
Recovery and non-recovery drip systems (sometimes called top feed systems) are also widely used. A pump on a timer pushes the solution through tubes which drip the solution at the root of each plant. The solution drains down through the growing medium in the grow tray and is either recovered back in the reservoir or is entirely used by the plant. The recovery system is more efficient as it reuses the solution. Drip systems can be used for large-scale growing of many different kinds of plants.
Aeroponics systems do not use a growing medium or grow tray. Rather, plants are suspended in containers and the roots are misted periodically with the nutrient solution. This is easily the most high-tech of all hydroponic systems. A timer connected to a pump times the misting which is done every few minutes to prevent the roots drying out. Aeroponic systems are most often used in labs, and have not been used as widely in commercial operations because of the expense in setting up the system. NASA has also experimented in using aeroponic systems for space use. These systems are ideal for efficient use of greenhouse space as the plants use vertical space as well as horizontal space.
Advantages and Disadvantages of Hydroponic Farming
Many hydroponic systems, such as the aeroponic and NFT systems, have a high start-up cost because of the need for pumps, tubing and timers. Active systems also require higher maintenance in the form of supervision (of pumps and timers), pH testing of recycled nutrient solution, and support of the plants. In systems that require growing medium, that medium is usually replaced after each crop. Hydroponics is also more involved and complicated than traditional dirt farming.
Despite the disadvantages, hydroponics has many useful applications. The biggest advantage is the ability to grow crops in areas that typically have poor soil quality and plants can be grown outside of their normal growing areas (deserts or extremely cold climates). Hydroponic farms yield many more crops than traditional dirt farm, given the same size farm. For example, one acre of hydroponic farm can yield as many as ten thousand plants compared to one third that number on a dirt farm (Archimedes). The implications of these numbers are huge for food production, especially in areas where crops do not typically grow well. In addition, crop rotation becomes obsolete because there is no soil from which nutrients are depleted.
All in all, hydroponic farming has many advantages that continue to be studied and explored for our future food production both on Earth and in space. Hydroponic systems also allow apartment dwellers or residents of small homes and yards to grow some of their own vegetables, a definite advantage for some families in this time of health hazards in our food, economic crises, and limited space. Clearly there are many hydroponic systems for many different situations and plants, enough that any application or family will find out that suits their needs.
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