by Dr Lynette Morgan
Introduction
Nutrients are the basis of any hydroponic system and since we need to meet all of the plants nutritional requirements, its important to know what you are suppling and what can go wrong. With any nutrient solution the two factors to keep in mind are firstly the composition of your nutrient - does it contain all of the elements required for plant growth in the correct ratios. And secondly, with your balanced and complete nutrient solution, what strength or `EC' should it be running at for your particular crop, stage of growth and type of hydroponic system, and how do we measure this.
The Nutrient Solution - Composition
Many growers prefer to buy a `pre-mixed' nutrient solution which simply needs to be diluted (for liquid concentrates) or dissolved in water before use. Often these `pre-made' nutrients come in 2, 3 , 4 or even more `parts' so a grower can change the ratio of the mineral elements to allow for either vegetative or fruiting growth or for different crops. There are many excellent brands of these pre-mixed nutrients on the market, however, many growers have come across major problems when they try to use some of the `indoor plant food' or other nutrients which have been designed for plants growing in soil or a pre fertilised potting mix. Often these types of products are not suitable for hydroponics because they are not designed to be a `complete plant food'. It is always preferable to buy a nutrient mix which is sold especially for `hydroponic' use, and is a `complete' plant food. To be `complete' a hydroponic nutrient needs to have the essential elements for plant growth these are:
Nitrogen (N)
Potassium (K)
Phosphorus (P)
Calcium (Ca)
Magnesium (Mg)
Sulphur (S)
Iron (Fe)
Manganese (Mn)
Copper (Cu)
Zinc (Zn)
Molybdate (Mo)
Boron (B)
Chlorine (Cl)
The levels that these elements are present in your hydroponic nutrient tend to vary between brands, since there is no one single recommendation for concentrations. Many nutrients may also contain some of the `beneficial elements' such as Nickel (Ni), Cobalt (Co), Silica (Si) or Selenium (Se). While these are not `essential' (plants will still grow without them), they can be beneficial to many crops.
Nutrient problems
Whether you make your own nutrient solution from the different fertiliser salts, or buy a premade brand, problems can, and often do, arise with deficiencies of one of more of the nutrient elements. Common reasons for this are that (1) the nutrient strength may be too low, resulting in insufficient nutrients for the plants in general. (2) The nutrient formula you are using may not be completely balanced, and one (or more of the elements) may be deficient. (3) Occasionally, growers may unintentionally leave out one of the fertiliser salts or the wrong fertiliser was used when the nutrient formula was weighted out. And just to complicate matters further, even if your solution is well balanced, sometimes environmental and internal plant conditions prevent the uptake of certain nutrients and deficiency symptoms then result.
Signs of deficiency
Each of the mineral elements required by the plant has its own set of `deficiency signs and symptoms' and growers can learn to identify many of these. Many of the signs are similar in appearance, but others are very distinct and most good gardening and hydroponic books will detail what these signs are. Briefly the deficiently symptoms for each of the elements are listed below (these may vary slightly between different plant species and depending on how severe the deficiency is):
