Hydroponics is defined as growing plants, using mineral nutrient solutions, without soil. Although hydroponic systems do not involve soil, they may involve a wide variety of growing media, such as perlite, gravel, peat, sand, rockwool and others. Typical hydroponic crops include lettuce, strawberries, hebrs, tomato, cucumber and flowers. In hydroponic systems which do not involve any growing medium, roots are immersed in an aerated nutrient solution. In hydroponic systems, most of the plant nutrients are supplied by the nutrient solution, rather than by the media in which the plants are grown.
Unlike soil, that stores nutrients, the growing media used in hydroponic systems have a little effect, if any, on the nutrition of plants. As a result, the only source of nutrients is the nutrient solution, and therefore you have total control over your plant nutrition.
While soil allows more tolerance for inaccuracy, hydroponics leaves very little room for errors. Because changes are rapid and mistakes can be very costly, hydroponics growers should make highly educated and accurate decisions
Types of Hydroponic Systems
There are two main types of hydroponic systems - closed hydroponic systems and open hydroponic systems. Hydroponic systems that do not involve growing media are usually closed systems, while hydroponic systems that involve growing media (container plants), may be closed or open systems
Closed Hydroponic Systems
Closed hydroponic systems the same nutrient solution is recirculated and the nutrient concentrations are monitored and adjusted accordingly.
Keeping the nutrient balance in such hydroponic systems is a challenge and the hydroponic nutrient solution has to be sampled and analyzed at least once a week. The nutrient solution composition has to be adjusted according to the results. If not managed properly, the nutrient solution might get out of balance. Closed hydroponic systems include both simple hydroponic systems, as well as sophisticated ones. Here is a short brief of some of these methods:
Deep Water Culture (DWC) hydroponic systems – This is the most simple type hydroponic systems. In this type of hydroponic systems plants are suspended in an oxygen-enriched nutrient solution.
The Wick hydroponic systems – This is a passive hydroponic system, in which wicks run from the base of the plant container down to a reservoir and draw the nutrient solution upwards.
Ebb and Flow – This is the most popular hydroponic system due to its low maintenance and low cost. It is widely used for plug production and potted plants. In this type of system the growing bed is flooded with nutrient solution and then it is allowed to drain. The duration and frequency of the flood depends on factors such as the type of growing medium used, size of containers and plants water requirements.
NFT (Nutrient Film Technique) hydroponic systems – This system uses a continuous nutrient solution flow over the roots. This results in a thin film of nutrient solution around the roots, allowing them both aeration and access to nutrients.
Open hydroponic Systems
In open hydroponic systems a fresh nutrient solution is introduced for each irrigation cycle. The nutrient solution is usually delivered to the plants using a drip system. In open hydroponic systems an adequate run-off must be maintained in order to keep nutrient balance in the root zone.
Hydroponic Nutrient Solutions
Several important factors have to be considered when preparing hydroponic nutrient solutions:
- Water quality – salinity, concentration of potential harmful elements (like sodium, chlorides and boron)
- Required nutrients and their concentrations in the hydroponic nutrient solution.
- Nutrient balance.
- The pH of the hydroponic nutrient solution and its affect on uptake of nutrients by plants.
The Electrical Conductivity (EC) of the Hydroponic Nutrient Solution
The electrical conductivity is a measure of the total salts dissolved in the hydroponic nutrient solution. It is used for monitoring applications of fertilizers. Note that the EC reading doesn’t provide you with information regarding the exact mineral content of the nutrient solution.
In closed hydroponics systems, the hydroponic nutrient solution is recirculated and elements which are not absorbed in high quantities by plants (such as sodium, chloride, fluoride etc.) or ions released by the plant, build up in the hydroponic nutrient solution. In this case there is a need more information about the nutrient solution content, that EC cannot provide.
Testing the hydroponic nutrient solution frequently will help you decide on the timing for replacing the nutrient solution or dilute it with fresh water water.
pH of the Hydroponic Nutrient Solution
The optimal pH range of the hydroponic nutrient solution is 5.8-6.3. Micronutrients are more available in lower pH, but when pH levels drop below 5.5, you run the risk of micronutrients toxicity, as well as impaired availability of calcium and magnesium. In hydroponics, especially in closed systems, the roots readily affect the hydroponic solution pH, so pH tend to fluctuate.
Appropriate products for acidifying the hydroponic nutrient solution are sulfuric acid, phosphoric acid and nitric acid. Ammonium/nitrate is one of the major factors affecting the pH of the nutrient solution
The hydroponic nutrient solution consists of minerals in the raw water and nutrients added with fertilizers. The selection of fertilizers and their concentration in the hydroponic nutrient solution greatly depend on the quality of the raw water. Therefore, testing the raw water prior to deciding on a fertilizer formula is imperative.
Minerals such as calcium, magnesium,sulfur, and trace elements such as boron, manganese, iron and zinc may be present in the source water. These elements must be factored in when adjusting the hydroponic nutrient solution.
Additionally, raw water might contain high concentrations of unwanted minerals, such as sodium, chloride or fluoride, rendering it unsuitable for hydroponics