Borgmann Aquaponics Hydroponics
First, we look at the nutrient solutions, some of which have existed for over a hundred years. This shows us the concentrations in which measurement must take place.
This serves as an initial orientation as to which nutrients or elements must be contained in a solution. A further step is the precise observation of plant growth in order to be able to identify deficits as such.
The next step is to get an idea of which elements, and consequently which compounds, are present in the end product. Such an analysis (the plant is put into a blender and mixed with additional chemicals depending on the compounds sought) unfortunately has the drawback that it does not really reveal everything we are interested in. This is because chemical compounds are rarely found in the plant in the same form in which they were originally added. This is where biology comes into play. As an example, we only mention the citric acid cycle here, which we do not want to withhold from you. It illustrates the complexity of metabolism.
Nutrition of hydroponic plants
When growing in containers, plant nutrition is provided via an aqueous solution of inorganic nutrient salts. Due to the absence of fine organic soil components, the chemical soil properties deviate significantly from the natural state, so normal plant fertilizer is only conditionally suitable for hydroponics.
A special hydroponic fertilizer provides a remedy, buffering the pH value of the solution in a range suitable for many plants through additives. So-called ion exchange granules are also used for this purpose, which supply the plants with nutrients via ion exchange while binding minerals present in the water that are incompatible with plants in excess, such as lime.
During the microbial conversion of ammonium ions into nitrate ions, oxygen is consumed, which is then lacking for root respiration. Therefore, fewer ammonium salts are used as nitrogen fertilizers in hydroponic fertilizers, rather nitrates.
In hydroponics, the electrical conductivity of the nutrient solution is usually constantly monitored. If the concentration of dissolved substances increases (for example, due to exudates or extraction from the soil), the solubility of oxygen in the nutrient solution decreases. With overly concentrated solutions, it becomes more difficult for plants to absorb water (see also osmosis). Furthermore, different stages of the plant require different conductivity of the nutrient solution depending on the variety, for example cuttings about 0.2–0.4 mS/cm, which can increase up to 2.4–2.6 mS/cm by the time of fruit formation. The morphology of plant growth also depends on the concentration of the nutrient solution, for example, whether compact or elongated plants grow. If the nutrient solution is too concentrated, it can be diluted with deionized water or rainwater.
Depending on the nutrient composition, the expected concentrations are in the following orders of magnitude:
| Element / Compound | Designation | mmol/L | mg/L (ppm) |
|---|---|---|---|
| Macronutrients | |||
| K | Potassium | 3 – 8 | 117 – 313 |
| Ca | Calcium | 1 – 4 | 40 – 160 |
| Mg | Magnesium | 0.5 – 1.5 | 12 – 36 |
| P | Phosphorus | 0.3 – 1.5 | 9.3 – 46.5 |
| S | Sulfur | 0.5 – 2 | 16 – 64 |
| Trace elements | |||
| Fe | Iron | 0.010 – 0.040 | 0.56 – 2.24 |
| Cu | Copper | 0.0005 – 0.002 | 0.03 – 0.13 |
| Zn | Zinc | 0.001 – 0.008 | 0.07 – 0.52 |
| Mn | Manganese | 0.001 – 0.008 | 0.06 – 0.44 |
| B | Boron | 0.010 – 0.045 | 0.11 – 0.49 |
| Mo | Molybdenum | 0.0001 – 0.001 | 0.01 – 0.10 |
| Nitrogen compounds | |||
| NO₃ | Nitrate | 0.8 – 3.2 | 50 – 200 |
| NO₂ | Nitrite | 0 – 0.22 | 0 – 10 |
| NH₄ | Ammonium | 0.06 – 1.11 | 1 – 20 |
| Fertilizer salts and chelates | |||
| KNO₃ | Potassium nitrate | 0 – 8 | 0 – 809 |
| Ca(NO₃)₂ | Calcium nitrate | 0 – 8 | 0 – 1312 |
| MgSO₄ | Magnesium sulfate | 0.5 – 2 | 60 – 241 |
| Fe-EDTA | Iron chelate | 0.010 – 0.040 | 3.5 – 14 |
| H₃BO₃ | Boric acid | 0.010 – 0.045 | 0.62 – 2.78 |
| MnSO₄ | Manganese(II) sulfate | 0.001 – 0.008 | 0.17 – 1.35 |
| ZnSO₄ | Zinc sulfate | 0.001 – 0.008 | 0.16 – 1.29 |
| CuSO₄ | Copper sulfate | 0.0005 – 0.002 | 0.08 – 0.32 |
| KCl | Potassium chloride | not common in nutrient solutions (chloride limited) | |
| FeSO₄ | Iron(II) sulfate | chelated form (Fe-EDTA/Fe-DTPA) preferred | |
| NH₄H₂PO₄ | Ammonium dihydrogen phosphate | 0 – 2 | 0 – 230 |
| (NH₄)₂HPO₄ | Diammonium hydrogen phosphate | 0 – 2 | 0 – 264 |
| MoO₃ | Molybdenum oxide | 0.0001 – 0.001 | 0.014 – 0.144 |
To convert the quantities (mg, ppm, mol, etc.) we have created some articles here for you. You can also find corresponding "stoichiometry" calculators on the internet, for example here: https://www.omnicalculator.com/chemistry/ppm-to-molarity
Here are some recipes for nutrient solutions...
Nutrient solution according to Wilhelm Knop
One liter of finished solution contains:
1.00 g Ca(NO3)2 Calcium nitrate
0.25 g MgSO4 * 7 H2O Magnesium sulfate
0.25 g KH2PO4 Potassium dihydrogen phosphate
0.25 g KNO3 Potassium nitrate
Trace FeSO4 * 7 H2O Iron(II) sulfate
1.00 g Ca(NO3)2 Calcium nitrate
0.25 g MgSO4 * 7 H2O Magnesium sulfate
0.25 g KH2PO4 Potassium dihydrogen phosphate
0.25 g KNO3 Potassium nitrate
Trace FeSO4 * 7 H2O Iron(II) sulfate
Medium according to Pirson and Seidel
One liter of finished solution contains
1.5 milliMol KH2PO4
2.0 mM KNO3
1.0 mM CaCl2
1.0 mM MgSO4
18 μM Fe-Na-EDTA
8.1 μM H3BO3
1.5 μM MnCl2
1.5 milliMol KH2PO4
2.0 mM KNO3
1.0 mM CaCl2
1.0 mM MgSO4
18 μM Fe-Na-EDTA
8.1 μM H3BO3
1.5 μM MnCl2
Nutrient medium according to Epstein
One liter of finished solution contains
1 mM KNO3
1 mM Ca(NO3)2
1 mM NH4H2PO4
1 mM (NH4)2HPO4
1 mM MgSO4
0.02 mM Fe-EDTA
0.025 mM H3BO3
0.05 mM KCl
0.002 mM MnSO4
Trace elements:
0.002 mM ZnSO4
0.0005 mM CuSO4
0.0005 mM MoO3
1 mM KNO3
1 mM Ca(NO3)2
1 mM NH4H2PO4
1 mM (NH4)2HPO4
1 mM MgSO4
0.02 mM Fe-EDTA
0.025 mM H3BO3
0.05 mM KCl
0.002 mM MnSO4
Trace elements:
0.002 mM ZnSO4
0.0005 mM CuSO4
0.0005 mM MoO3
Trace element addition according to D. R. Hoagland (1884–1949)
One liter of finished solution contains
55 mg Al2(SO4)2
28 mg KJ
28 mg KBr
55 mg TiO2
28 mg SnCl2 · 2 H2O
28 mg LiCl
389 mg MnCl2 · 4 H2O
614 mg B(OH)3
55 mg ZnSO4
55 mg CuSO4 · 5 H2O
59 mg NiSO4 · 7 H2O
55 mg Co(NO3)2 · 6 H2O
55 mg Al2(SO4)2
28 mg KJ
28 mg KBr
55 mg TiO2
28 mg SnCl2 · 2 H2O
28 mg LiCl
389 mg MnCl2 · 4 H2O
614 mg B(OH)3
55 mg ZnSO4
55 mg CuSO4 · 5 H2O
59 mg NiSO4 · 7 H2O
55 mg Co(NO3)2 · 6 H2O
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