Hydroponic nutrient solutions
The hydroponic nutrient solution is the sole source of nutrients to the plant; therefore it is imperative that a balanced solution, containing all the right plant nutrients, is applied.
Several important factors have to be considered when choosing fertilizers and preparing a hydroponic nutrient solution:
- 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 the uptake of nutrients by plants.
In Smart Fertilizer software, you can upload your water test. The software will assess the parameters of your water such as pH and EC together with the nutrient status and eventual presence of toxicities. This helps to create a fertilization recipe ad-hoc for your irrigation water.
Standard nutrient solutions
There are various standard nutrient solutions, such as the Hoagland solution (1933), Steiner (1961), Bollard (1966) and others. These standard solutions are good as a general guideline, but are not adapted to specific growing conditions.
Even if you decide to use one of the standard nutrient solutions, make sure to use the nutrient concentration as a guideline, and not the fertilizer recipe that corresponds to them. The initial composition of the raw water that you use will affect the actual nutrients that have to be added with fertilizers.
Common nutrient ranges in hydroponic nutrient solutions
| Element | Ionic form absorbed by plants | Common range (ppm=mg/l) |
|---|---|---|
| Nitrogen | Nitrate (NO3–), Ammonium (NH4+) | 100-250 ppm elemental N |
| Phosphorus | Dihydrogen phosphate (H2PO4–) Phosphate (PO43-) Monohydrogen phosphate (HPO42-) | 30-50 ppm elemental P |
| Potassium | Potassium (K+) | 100-300 ppm |
| Calcium | Calcium (Ca2+) | 80-140 ppm |
| Magnesium | Magnesium (Mg2+) | 30-70 ppm |
| Sulfur | Sulfate (SO42-) | 50-120 ppm elemental S |
| Iron | Ferrous ion (Fe2+) Ferric ion (Fe3+) | 1-5 ppm |
| Copper | Copper (Cu2+) | 0.04-0.2 ppm |
| Manganese | Manganese (Mn2+) | 0.5-1.0 ppm |
| Zinc | Zinc (Zn2+) | 0.3-0.6 ppm |
| Molybdenum | Molybdate (MoO42-) | 0.04-0.08 ppm |
| Boron | Boric acid (H3BO3) Borate (H2BO3–) | 0.2-0.5 ppm elemental B |
| Chloride | Chloride (Cl–) | <75 ppm |
| Sodium | Sodium (Na+) | <50 ppm TOXIC to plants |
Suggested Nutrient Solutions for Various Crops
| Crop | N | P | K | Ca | Mg |
| Concentration in mg/l (ppm) | |||||
| Tomato | 190 | 40 | 310 | 150 | 45 |
| Cucumber | 200 | 40 | 280 | 140 | 40 |
| Pepper | 190 | 45 | 285 | 130 | 40 |
| Strawberry | 50 | 25 | 150 | 65 | 20 |
| Melon | 200 | 45 | 285 | 115 | 30 |
| Roses | 170 | 45 | 285 | 120 | 40 |
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 re-circulated 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 more information about the nutrient solution content is required, and this cannot be provided by the EC. Testing the hydroponic nutrient solution frequently will help you decide on the timing for replacing the nutrient solution or diluting it with fresh 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 the impaired availability of calcium and magnesium.
In hydroponics, especially in closed systems, the roots readily affect the hydroponic solution pH, so pH tends to fluctuate.
Appropriate products for acidifying the hydroponic nutrient solution are sulfuric acid, phosphoric acid and nitric acid.
Water quality
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 depends 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.
This can be solved by diluting the water with a pure water supply or pre-treating the raw water with desalination or ion-exchange.
In Smart Fertilizer software, we created a specific section for hydroponic and fertigation where for each growth stage we suggest different amounts of nutrients but also different pH and EC (Electrical Conductivity). In this section, there is also a feature called ‘Drainage Tool’ which helps in understanding and re-adjusting the fertigation automatically according to the analysis of the ‘drained solution’ from your substrate/pot.
- Recommends the ideal fertilizer mixture/ blends
- Saves up to 50% on fertilizer costs
- Comprehensive data on hundreds of crop varieties
- Interprets test results for any extraction method
