The Agricultural Research Council defines ‘hydroponics’ as “a system where plants are grown in growth media other than natural soil”. All nutrients supplied to the plants are dissolved in the irrigation water. Liquid hydroponic systems have no supporting medium for the roots. Instead, an inert aggregate material with a solid granular structure, such as sand, gravel, vermiculite, perlite or sawdust, supports the roots. Hydroponics is an open system; the surplus nutrient solution delivered to the plant roots is recovered, replenished and recycled.
In hydroponic production, the nutrient levels supplied to the plants are determined directly. The yield is consequently far higher than that of a similar crop grown in soil.
Hydroponics principles
A plant obtains its nutrients by converting carbon dioxide, light and water into carbohydrates through the process of photosynthesis. With hydroponics, a plant gets its nutrients from the nutrient-rich water. The absence of soil also means that the hydroponic system must physically support the plant while allowing the root to have maximum contact with the nutrient solution. A ‘growth medium’ that aids moisture and nutrient retention is often used for this. In South Africa, hydroponic vegetable production is almost always carried out in some type of enclosure.
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