
| 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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