All plants need 16 elements to grow. They are C, H, O, N, P, K, Ca, Mg, S, Zn, Cu, Fe, Mn, B, Mo and Cl). In nature, the plants derive these elements from the atmosphere or minerals in the soil. Most of the elements used in preparing nutrient solutions are derived from these naturally occurring minerals. So only they are called as mineral nutrients. As such, they are not only natural but also very safe. They are sometimes purified to remove the impurities.
There are numerous formulations of nutrient solutions available in the market. This is based on the availability and price of the raw materials. Some are in solid form as nutrient salts or fertilizers, some in liquid form and some in tablet form. In most cases they are inorganic. Sometimes they are purely organic and sometimes they are a mixture of both. The manufacturers generally tend to maintain the secrecy of their formulation. Certainly, there is no magic. All nutrient solutions contain the essential nutrient elements needed for plant growth.
Their composition depends on the raw materials and the intended purpose. Normally, nutrient solution for vegetative growth will have more nitrogen and less potassium and those for flowering and fruiting phase will have less nitrogen and more potassium.
The formulation of a typical "standard nutrient solution" is given in Table 2. Dr. Alan Cooper proposed this formulation for his NFT hydroponic system. It works well in the tropical as well as the temperate regions.
This formulation is to be prepared in 1000 liters of water and is ready for feeding to the plant. However, in practice, the solution is concentrated 100 times i.e. the amount of nutrients are dissolved in 10 liters of water.
In concentrated form, chemical reaction might take place. Hence, it is recommended to dissolve calcium nitrate and EDTA iron in 10 litres of water and label them as "NUTRIENT SOLUTION - A" and the rest of the nutrients in another 10 litres of water and label them as NUTRIENT SOLUTION - B . These are called Stock Solutions.
When feeding this solution to the plants, Solution A and B should be diluted 100 times in equal volumes. First, add Solution A. Stir well and next add Solution B. The exact volume to be added will depend on the final volume of nutrient solution required for the hydroponics system.
Incidentally, all elempon are present in the nutrient solution as ions. An electrical conductivity meter (EC meter) is often used to measure the total concentration all ions in the solution in micro Siemen (mS/cm) or milli Siemens (mS/cm). In the US, they use the Conductivity Factor (CF) which is ten times the mS value. In Europe, units like moles and milli equivalents used.
As a thumb rule, 5 ml (one teaspoon full) each of the Stock Solution A and B in one litre of water will give a concentration of EC 1.0 mS/cm, which is just nice to start any plant.
For a small unit using the Static Aerated Technique (SAT), the solution should be changed once a fortnight. For large units using other techniques, the nutrient solution can be recycled by topping-up with the Stock Solutions every week. The EC level should range from 1.5 - 3.5 mS/cm depending on the type of the crop and the stage of the crop. However, plants themselves are the best indicators. Observe them and adjust the concentration accordingly.
| Nutrient Chemicals | Weight in grams |
|---|---|
| Potassium dihydrogen phosphate | 263.00 |
| Potassium nitrate | 583.00 |
| Calcium nitrate | 1003.00 |
| Magnesium sulphate | 513.00 |
| EDTA iron | 79.00 |
| Manganous sulphate | 6.10 |
| Boric acid | 1.70 |
| Copper sulphate | 0.39 |
| Ammonium molybdate | 0.37 |
| Zinc sulphate | 0.44 |