Nutrients Plants Require for Growth
Plants require seventeen essential elements for growth: carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg), boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), and zinc (Zn). These elements, also called nutrients, are often split into three groups (Figure 1). The first group is the three macronutrients that plants can obtain from water, air, or both—carbon (C), hydrogen (H), and oxygen (O). The soil does not need to provide these nutrients, so they are not sold as fertilizers.
The other fourteen essential elements are split into two groups—soil-derived macronutrients and soil-derived micronutrients. This split is based on the actual amount of nutrient required for adequate plant growth. The soil-derived macronutrients are nitrogen, phosphorus, potassium, sulfur, calcium, and magnesium. The soil-derived micronutrients are boron, chlorine, copper, iron, manganese, molybdenum, nickel, and zinc.
The six soil-derived macronutrients are present in plants at relatively high concentrations—normally exceeding 0.1 percent of a plant’s total dry weight. This translates into a minimum need of 20 lbs of each macronutrient per acre each year.
Nitrogen—Plants require large amounts of nitrogen for adequate growth. Plants take up N from the soil as NH+4 (ammonium) or NO-3 (nitrate) (Table 1). A typical plant contains 1.5 percent nitrogen on a dry-weight basis, but this can range from 0.5 percent for a woody plant to up to 5.0 percent for a legume.
|Essential nutrient||Uptake form||Plant content (dry weight)|
|Phosphorus||H2PO-4, HPO2-4, PO3-4||0.2||0.1–0.5|
|Boron||H3BO3, H2BO2-3, HBO2-3||20||2–100|
Nitrogen is a component of amino acids, which link together to form proteins. Nitrogen is also a component of protoplasts and enzymes (Table 2). Once in the plant, N is mobile—it can move from older plant tissue to new tissue. Consequently, if N is deficient in plants, the older leaves often turn yellow green or yellow first. As the deficiency progresses the entire plant yellows.
|Essential nutrient||Mobility in plant||Function of plant|
|Nitrogen||good||proteins, protoplasts, enzymes|
|Phosphorus||good||ATP, ADP, basal metabolism|
|Potassium||good||water relations, energy relations, cold hardiness|
|Sulfur||fair/good||proteins, protoplasts, enzymes|
|Calcium||very poor||cell structure, cell division, cell elongation|
|Boron||very poor||sugar translocation, cell development, growth regulators|
|Iron||poor||chlorophyll synthesis, metabolism, enzyme activation|
|Manganese||poor||Hill reaction-photosystem II, enzyme activation|
|Molybdenum||poor||nitrogen fixation, nitrogen use|
|Zinc||poor||protein breakdown, enzyme activation|
The major natural source of N in soils is organic matter (Table 3). Nitrogen is the nutrient generally most limiting in agronomic, horticultural, and home and garden situations in the Pacific Northwest.
|Essential nutrient||Typical soil content||Extent of deficiencies|
|Nitrogen||1%–2% organic matter*||widespread|
|Phosphorus||1–4 ppm (Morgan soil test)
4–20 ppm (Olson soil test)
|widespread; low pH (<5.5) soils; high pH (>6.5) soils|
|Potassium||>100 ppm||isolated to potatoes, alfalfa, high pH|
|Boron||0.1–0.7 ppm||low organic matter soils or high precipitation|
|Copper||1.0–3.0 ppm||soils with over 8% organic matter|
|Iron||plenty in low pH soils||high pH (>7.5) soils; ornamentals in urban areas|
|Molybdenum||no soil test||when growing legumes in soils with pH <5.4|
|Nickel||no soil test||no problems|
|Zinc||0.3–2.0 ppm||where topsoil has been removed|
|*Each 1 percent of soil organic matter will supply between 20 and 22 lbs/ac N for plant growth.|
Phosphorus—A typical plant contains 0.2 percent P on a dry-weight basis (Table 1); however, depending on the plant species this value can range from 0.1 to 0.5 percent. Plants take up P as an anion (ion with a negative charge)—H2PO-4, HPO2-4, or PO3-4. The actual form of the anion is dependent on soil pH.
Phosphorus is mobile within plants and can travel from old plant tissue to new plant tissue on demand (Table 2). P deficiency in plants is hard to diagnose by eye because deficiency symptoms are not commonly visible. A phosphorus-deficient plant is likely to be dark green but have stunted growth. Phosphorus is essential for ADP, AMP, and basal metabolism in plants.
Phosphorus deficiencies in soils can be diagnosed with a soil test. Phosphorus availability is related to soil pH. In general, soils with pH values between 5.5 and 6.5 have adequate levels of plant-available P. However, P availability is much lower in soils with pH values below 5.5 or above 6.5 (Table 3).
Potassium—Plants typically contain 1.0 percent K on a dry-weight basis (Table 1). This value can range from 0.5 to 5.0 percent depending on the plant species. Potassium is held by the clays in soils and is taken up by plants as K+.
Potassium is mobile in plants (Table 2). Potassium deficiencies can be diagnosed by looking at the older plant tissue. Deficiencies appear along the outer margins of older leaves as streaks or spots of yellow (mild deficiencies) or brown (severe deficiencies). Potassium plays several roles in plants. It is important for water and energy relationships and has been linked to improved cold hardiness.
Soils in the Pacific Northwest generally contain adequate amounts of potassium (Table 3). Deficiencies are isolated to soils where alfalfa and potatoes have been grown for several decades.
Sulfur—Plants take up S from the soil as SO2-4 (sulfate) (Table 1). Because the plant-available form of S is negatively charged, it can be leached out of plant root zones with precipitation or irrigation. A typical plant contains 0.1 percent S on a dry-weight basis, but this can range from 0.05 to 0.5 percent S.
Sulfur, like N, is a component of some amino acids that link together to form proteins. Sulfur is also a component of plant protoplasts and enzymes (Table 2). Once in the plant, sulfur has only fair mobility. New plant tissue will show an S deficiency first, often turning yellow green or yellow.
Sulfur is widely deficient in soils in the Pacific Northwest (Table 3). Low levels of soil organic matter or excessive watering can produce deficiencies.
Calcium—A typical plant contains 0.5 percent Ca on a dry-weight basis (Table 1). However, woody plants may contain up to 5.0 percent Ca. Plants take up calcium as Ca2+. Calcium is required for cell division, cell elongation, and cell structure (Table 2). Since Ca is not mobile in plants, calcium deficiency symptoms appear at their growing tips.
Soils in the Pacific Northwest contain plenty of calcium (Table 3). Consequently, calcium deficiencies in plants grown under agronomic, horticultural, or lawn and garden situations have never been observed in the region.
Magnesium—Plants typically contain 0.2 percent Mg on a dry-weight basis (Table 1). This value can range from 0.1 to 1.0 percent depending on the plant species. Magnesium is held by the clays and organic matter in soils and is taken up by plants as Mg2+.
Magnesium is mobile in plants (Table 2). Magnesium deficiencies can be diagnosed by looking at the older plant tissue. Deficiencies appear as “interveinal chlorosis” in older leaves—the veins of the leaves stay dark green while the areas between the veins appear yellow green, yellow, or white. Magnesium is a component of chlorophyll.
Most soils in the Pacific Northwest contain adequate amounts of Mg for plant growth (Table 3). Magnesium deficiencies are isolated to soils with pH values below 5.2.
The eight soil-derived micronutrients are present in plants at relatively low concentrations—often just a few parts per million (ppm) of a plant’s total dry weight. Even though plants require only small amounts of micronutrients, a deficiency will harm them as much as a lack of N or P. Plants need 0.5 to 2 lbs/ac of most micronutrients per year.
Boron—Plants require about 20 ppm of B (Table 1). Boron is taken up by plants as an uncharged molecule (H3BO3) or as an anion (H2BO-3, HBO2-3). Since the plant-available form of B is not positively charged it can be leached out of soils and is often lost from the plant root zone by overirrigation or high precipitation.
Boron promotes the translocation of sugars and cell development and is believed to be important for growth regulators (Table 2). Boron is not mobile in plants. Consequently, B deficiency symptoms most often appear on the growing tip of the plant. In B-deficient plants, the growing tip is often deformed.
Soils that contain less than 1.5 percent organic matter or are overirrigated tend to be deficient in B (Table 3). Boron deficiencies are common on agronomic crops, in fruit trees, and in urban gardens. For additional information on B, see University of Idaho CIS 1085, Boron in Idaho.
Chlorine—Plants generally contain about 100 ppm of chlorine (Table 1). Plants take up chlorine as Cl- and require it for photosynthesis (Table 2). Chlorine is plentiful in soils in the Pacific Northwest. Consequently, Cl deficiencies in plants will not be encountered.
Copper—Copper is taken up by plants as Cu2+ (Table 1). Concentrations of Cu in plants average 6 ppm, but can range from 2 to 20 ppm. Copper is a component of plant cytochromes and is needed for enzyme activation. Copper is not mobile in plants; deficiencies appear first in the youngest plant tissue (Table 2).
Most soils contain adequate levels of Cu for plant growth (Table 3). Copper deficiencies are most likely in soils that contain more than 8 percent organic matter—only about 1 percent of the soils in the Pacific Northwest. For additional information on Cu, see University of Idaho CIS 682, Copper in Idaho. (out of print)
Iron—Plants take up iron as Fe2+ (Table 1). A typical plant contains 100 ppm of Fe, but Fe content ranges from 50 to 1,000 ppm depending on plant species. Iron is needed for chlorophyll synthesis, metabolic processes, and enzyme activation (Table 2). Iron is not mobile in plants, so Fe deficiencies first appear on younger leaves. The characteristic deficiency symptom is interveinal chlorosis on the younger leaves.
In general, there is plenty of plant-available Fe in acid and neutral pH soils (Table 3). In the Pacific Northwest Fe deficiencies are often observed in fruit trees, golf course greens, and ornamental plantings in urban areas. Iron deficiencies should be corrected with foliar sprays.
Manganese—Manganese is taken up as Mn2+ by plants (Table 1). Concentrations of Mn in plants average 50 ppm, but can range from 20 to 200 ppm. Manganese is required in the Hill reaction of photosystem II and is important for enzyme activation. Manganese is not mobile in plants, so deficiencies appear first in the youngest plant tissue (Table 2).
Most soils contain adequate levels of Mn for plant growth (Table 3). Manganese deficiencies are not found in acid or neutral pH soils. The few observed Mn deficiencies in Idaho occur in alkaline soils that have high levels of organic matter (greater than 6%).
Molybdenum—Plants take up molybdenum as MoO2-4 (Table 1). A typical plant contains only 0.1 ppm of Mo. However, this small amount of Mo allows plants to utilize N. In addition, legumes require Mo for nitrogen fixation (Table 2).
Molybdenum is not mobile in plants, so deficiency symptoms appear in younger plant tissue first. Molybdenum-deficient plants turn yellow green to yellow. Most Mo deficiencies occur when legumes are grown in soils with pH values less than 5.4. For additional information on Mo, see University of Idaho CIS 1087, Molybdenum in Idaho.
Nickel—Nickel was added to the essential element list in 1991. Plants require less than 1 part per billion Ni. Nickel is believed to be important in iron metabolism in plants. Deficiencies have never been observed in the Pacific Northwest.
Zinc—A typical plant contains 20 ppm Zn on a dry-weight basis (Table 1). Plants take up zinc as Zn2+. Zinc is required for protein breakdown and in enzyme activation in plants (Table 2). Zinc is not very mobile in plants; consequently, deficiency symptoms first appear on the youngest plant tissue. Most soils in the Pacific Northwest contain adequate amounts of Zn (Table 3). However, Zn deficiencies do occur in soils where the topsoil or organic matter has been removed. For additional information about Zn, see University of Idaho CIS 1088, Zinc in Idaho.
Nitrogen, phosphorus, and sulfur are the macronutrients that will most likely limit plant growth in Idaho. Under certain conditions the micronutrients boron, iron, and zinc may also be deficient. When correcting a micronutrient deficiency, be careful not to overapply and induce a toxicity. The publications referred to in the text are available at the following University of Idaho website: https://www.uidaho.edu/extension/publications.
About the Author
Issued in furtherance of cooperative extension work in agriculture and home economics, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Barbara Petty, Director of University of Idaho Extension, University of Idaho, Moscow, Idaho 83844. The University of Idaho has a policy of nondiscrimination on the basis of race, color, religion, national origin, sex, sexual orientation, gender identity/expression, age, disability or status as a Vietnam-era veteran.
CIS 1124 | Published November 2004 | © 2021 by the University of Idaho