Hydroponic solutions are a central component of hydroponic farming, where plants grow in a soilless system and get their nutrients directly from an aqueous solution. These solutions contain all the essential macro and micro nutrients that plants need for growth. The main macronutrients include nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulfur (S), while the micronutrients include iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), boron (B) and molybdenum (Mo).
A hydroponic solution must be carefully formulated to ensure the optimal ratio of these nutrients to ensure plants grow healthily and produce high yields. The pH of the solution is also crucial and should be in the range of 5.5 to 6.5 to maximize nutrient uptake.
There are different types of hydroponic systems, such as NFT (Nutrient Film Technique), Deep Water Culture (DWC), and aeroponic systems, all of which rely on the use of hydroponic solutions. The exact composition of the solution can vary depending on the type of plant, growth stage, and specific conditions.
| element | role | Ionic form (s) | Low range (ppm) | High range (ppm) | Common sources | comment |
| Nitrogen | Essential macronutrient |
NO - 3
or
NH + 4
|
100 | 1000 | KNO 3, NH 4 NO 3, Ca (NO 3) 2, HNO 3, (NH 4) 2 SO 4 and (NH 4) 2 HPO 4 | NH + 4 interferes with Ca 2+ uptake and can be toxic to plants when used as the primary nitrogen source.A 3:1 ratio of NO - 3-N to NH + 4-N (wt%) is sometimes recommended to balance pH during nitrogen absorption.Plants respond differently depending on the form of nitrogen, e.g. ammonium has a positive charge and thus the plant will eject a proton (H + ) for each NH + 4 taken up, resulting in a reduction in rhizosphere pH.When supplied with NO - 3 the opposite can occur as the plant releases bicarbonate (HCO - 3), which increases rhizosphere pH.These changes in pH can affect the availability of other plant essential micronutrients (e.g. Zn, Ca, Mg). |
| potassium | Essential macronutrient | K + | 100 | 400 | KNO 3, K 2 SO 4, KCl, KOH, K 2 CO 3, K 2 HPO 4 and K 2 SiO 3 | High concentrations impair Fe, Mn and Zn function. Zinc deficiencies are often the most obvious. |
| phosphorus | Essential macronutrient | PO3−4 | 30 | 100 | K 2 HPO 4, KH 2 PO 4, NH 4 H 2 PO 4, H 3 PO 4 and Ca (H 2 PO 4) 2 | Excess NR - 3 tends to inhibit PO 3− 4 absorption.The ratio of iron to PO 3− 4 can affect co-precipitation reactions. |
| calcium | Essential macronutrient | Approx 2+ | 200 | 500 | Ca(NO3)2, Ca(H2PO4)2, CaSO4, CaCl2 | Excess Ca 2+ inhibits Mg 2+ uptake. |
| magnesium | Essential macronutrient | Mg2 + | 50 | 100 | MgSO 4 and MgCl 2 | Should not exceed the Ca 2+ concentration due to competitive uptake. |
| sulfur | Essential macronutrient | SO 2− 4 | 50 | 1000 | MgSO 4, K 2 SO 4, CaSO 4, H 2 SO 4, (NH 4) 2 SO 4, ZnSO 4, CuSO 4, FeSO 4 and MnSO 4 | Unlike most nutrients, plants can tolerate high concentrations of SO 2− 4 and selectively absorb the nutrient as needed. However, undesirable counterion effects still occur. |
| iron | Essential micronutrient | Fe3 + and Fe2 + | 2 | 5 | Fe DTPA, Fe EDTA, iron citrate, iron tartrate, FeCl 3, iron III EDTA and FeSO 4 | pH values above 6.5 greatly reduce iron solubility. Chelating agents (e.g. DTPA, citric acid or EDTA) are often added to increase iron solubility over a wider pH range. |
| zinc | Essential micronutrient | Zn2 + | 0.05 | 1 | ZnSO4 | Excess zinc is highly toxic to plants, but essential for plants in low concentrations. |
| copper | Essential micronutrient | Cu2 + | 0.01 | 1 | CuSO4 | Plant sensitivity to copper varies widely. 0.1 ppm can be toxic to some plants, while a concentration of up to 0.5 ppm is often considered ideal for many plants. |
| manganese | Essential micronutrient | Mn2 + | 0.5 | 1 | MnSO 4 and MnCl 2 | Absorption is increased by high PO 3− 4 concentrations. |
| boron | Essential micronutrient | B (OH) - 4 | 0.3 | 10 | H 3 BO 3 and Na 2 B 4 O 7 | However, some plants are an essential nutrient and are very sensitive to boron (e.g. citrus trees show toxic effects at 0.5 ppm). |
| molybdenum | Essential micronutrient | Mn - 4 | 0.001 | 0.05 | (NH 4) 6 Mo 7 O 24 and Na 2 MoO 4 | A component of the enzyme nitrate reductase, which is required by rhizobia for nitrogen fixation. |
| nickel | Essential micronutrient | Ni2 + | 0.057 | 1.5 | NiSO 4 and NiCO 3 | Essential for many plants (e.g. legumes and some cereals). Also used in the enzyme urease. |
| chlorine | Variable micronutrient | C1 - | 0 | Very variable | KCl, CaCl 2, MgCl 2 and NaCl | May interfere with NO - 3 uptake in some plants, but may be beneficial in some plants (e.g. in asparagus at 5 ppm).Absent in conifers, ferns and most bryophytes. |
| aluminum | Variable micronutrient | Al3 + | 0 | 10 | Al2(SO4)3 | Essential for some plants (e.g. peas, corn, sunflowers and cereals). May be toxic to some plants below 10 ppm. Sometimes used to make flower pigments (e.g. of hydrangeas). |
| silicon | Variable micronutrient | SiO 2− 3 | 0 | 140 | K 2 SiO 3, Na 2 SiO 3 and H 2 SiO 3 | Present in most plants, abundant in cereals, grasses and tree bark.Evidence that SiO 2− 3 improves resistance to plant diseases. |
| titanium | Variable micronutrient | T3 + | 0 | 5 | H 4 TiO 4 | May be essential, but trace amounts of Ti 3+ are so ubiquitous that its addition is rarely justified. At 5 ppm, beneficial growth effects are notable in some crops (e.g. pineapple and peas). |
| cobalt | Non-essential micronutrient | CO2 + | 0 | 0.1 | CoSO4 | Required for rhizobia, important for nodulation of legumes. |
| sodium | Non-essential micronutrient | Well + | 0 | Very variable | Na 2 SiO 3, Na 2 SO 4, NaCl, NaHCO 3 and NaOH | Na + can partially replace K + in some plant functions, but K + is still an essential nutrient. |
| Vanadium | Non-essential micronutrient | VO2 + | 0 | Trace, undetermined | VOSO4 | Beneficial for rhizobial N 2 fixation. |
| lithium | Non-essential micronutrient | Li + | 0 | Undetermined | Li 2 SO 4, LiCl and LiOH | Li + can increase the chlorophyll content of some plants (e.g. potato and pepper plants). |
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