Hydroponics: Methods of irrigation
There are various methods to suit differing needs.
Surface watering consists of applying water and nutrients from above the aggregate by means of a watering can with a rose, and removing the drainage plugs a few hours later to drain off excess liquid.
Auto-dilution surface watering is a refinement on the first method, the essential difference being that the water is fed onto the aggregate surface through a device which meters and injects concentrated nutrients into the water supply. This removes the need for storage tanks.
With drip culture, there are a number of variations, but the principle is the same: the nutrient solution is drip or trickle-fed onto the tray or bed from an upper tank and the surplus is caught in a sump, and returned to the top tank by means of a small pump. One of the problems here is the frequency with which the nozzles become blocked.
The continuous-flow system is a variation on the surface watering and sub-irrigation methods in which a tank or similar receptacle feeds the growing container through a hosepipe. The tank is raised above the container level to irrigate, and acts as a sump when lowered. This is useful for small units.
Sub-irrigation differs from the continuous flow system in that the nutrient solution is fed in from below the aggregate surface level, flooding the medium and then draining back into the reservoir to be recycled again.
In a wick system, the nutrient solution is carried by capillary action from a shallow tank to the roots via a wick made of glass-fibre or some other suitable material. There are other variations which also rely on capillary action. One system consists of growing plants on a net or bag of hydroleca, the bottom of which rests in a shallow layer of water and nutrient which is topped up with water or drained and renewed with dilute solutions as required.
The macro or major nutrients such as nitrogen, phosphorus, potassium, calcium, sulphur and magnesium are needed by all plants, just as withculture; but it is more important that, for example, potassium is supplied as a sulphate and not a chloride salt, because chloride acts as a poison in higher concentrations.
The biggest difference between hydroponics and normal soil culture is that in normal soil the trace elements, such as boron, copper and zinc, occur naturally due to weathering and breakdown. In soilless cultivation these trace elements, “although required only in minute quantities, have to be supplied, usually as slow-release ‘frits’ (which have the consistency of powdered glass) in the form of fertilizer.
The newcomer to hydroponics would do well to start with a proprietary made-up fertilizer mixture. Until experience of the system has been gained, mistakes in mixing up fertilizer can easily go undetected in the initial stages. However, the general principles of feeding plants are the same, whether they are grown in soil or hydroponically. The methods of fertilizer application, how- ever, differ in a number of ways.
The importance of using commercial-grade materials is that they contain sufficient trace elements, in the form of impurities, to avoid the necessity of having to prepare a special mixture.
The ingredients must be very thoroughly mixed, with any lumps broken up. The mixture should be used at the rate of 10 g (^ oz) to 4.5 L (1 gal) of water. This nutrient solution and any other should be renewed every 7-10 days. Some of the proprietary solutions may not need to be changed so often.
Always keep to the instructions for best results. Weigh the materials accurately and do not guess. As you gain experience, you can start to use more elaborate formulae, which can be found in specialized books on hydroponics.
You should always dissolve the ingredients in at least 75 percent of the total amount of water. For example, if making 16 L (3 gals) of solution, you should pour out at least 12 L (2-½ gals) of water before adding the chemicals.
A disadvantage of making your own nutrient solution is that some of the ingredients may not store well. Also, it will cost more to make small amounts of solution this way than to buy ready-mixed proprietary fertilizer powders. The commercial mixtures store more or less indefinitely as long as they are kept in sealed plastic bags in a cool bone-dry place, protected from direct sunlight.