Hydroponics & Nutrition > Introduction
Soil-less growing systems / hydroponics
Many greenhouse crops are not grown in the natural soil, but in a growing medium or substrate ('soil-less culture'), or alternatively in hydroponics or aeroponics ('water culture'). Possible growing media include rockwool, pumice, sawdust, peat, coco peat, foam and other synthetic materials, vermiculite, or a mixture, either in pots, bags, tubes or slabs. Most tomatoes, capsicum, cucumber and eggplants as well as many flowers crops are grown in a substrate. Water cultures are a special form of soilless cultures. They do not use any substrate, apart from a small amount (normally rockwool) for propagation. The plant roots hang in a layer of nutrient solution (in hydroponics) or are sprayed with a mist of nutrient solution (in aeroponics). Water cultures are especially used for lettuce and herbs.
Background
The reason of growing soilless is that control of root diseases is virtually impossible in soil, especially since agrichemicals such as methyl-bromide are banned. A soilless growing system can more easily be treated (or replaced) when there is a disease problem. Moreover, the production is often higher in a soilless system than in soil due to accurate control of the conditions in the root-zone as well as precise nutrient supply to the plants in a soilless system.
Nutrient solution
Because substrates contain no or little plant nutrients, these need to be supplied by so-called ‘fertigation’ (fertilisation + irrigation). Therefore a nutrient solution is supplied that contains the essential nutrients including six macro-elements (calcium, potassium, magnesium, nitrate, phosphate, sulphate) and six micro-elements (iron, copper, zinc, borium, manganese, molybdenium). The nutrient solution is usually made up in concentrated form in two large tanks and then automatically diluted with water, mixed and supplied through the irrigation system.
EC, CF, pH
The strength of the nutrient solution (expressed as EC or CF) is controlled by the dilution factor. The acidity (expressed as pH) is adjusted with automatic supply of acid or alkaline to the nutrient solution. The EC (or CF) and pH are measured in the root zone. Also the volume and frequency of irrigation cycles are varied according to the plant needs. With these variables, the grower can influence how plants grow and develop. Obviously everything is controlled by the computer.
Open or closed systems
There are two methods of dealing with the nutrient solution: open systems or run-to-waste systems and closed systems or recirculating systems. In open system, any surplus of nutrient solution is drained out and discharged. The closed systems recoup and re-use the surplus nutrient solution. Obviously closed systems are preferable, but it the technique is harder to master. There can be complications such accumulation of unwanted elements (e.g. sodium), or unnoticed deficiency of necessary elements, as well as spread of diseases.
Subpages and Further reading
Subpages and Articles (as PDF files) will be added by July 2008
