Plant Nutrition Info

Plant Nutrition is the study of the chemical elements that are necessary for growth. In 1972, E. Epstein defined 2 criteria for an element to be essential for plant growth:

  1. in its absence the plant is unable to complete a normal life cycle or
  2. that the element is part of some essential plant constituent or metabolite,

this is all in accordance with Liebig's law of the minimum.[1](i.e. - growth is controlled not by the total amount of resources available, but by the scarcest resource (limiting factor)). There are 17 essential plant nutrients. Carbon and oxygen are absorbed from the air, while other nutrients including water are obtained from the soil. Plants must obtain the following mineral nutrients from the growing media:[2]

  • the primary macronutrients: nitrogen (N), phosphorus (P), potassium (K)
  • the three secondary macronutrients: calcium (Ca), sulphur (S), magnesium (Mg)
  • the macronutrient Silicon (Si)
  • the micronutrients/trace minerals: boron (B), chlorine (Cl), manganese (Mn), iron (Fe), zinc (Zn), copper (Cu), molybdenum (Mo), nickel (Ni), selenium (Se), and sodium (Na)

The macronutrients are consumed in larger quantities and are present in plant tissue in quantities from 0.2% to 4.0% (on a dry matter weight basis). Micro nutrients are present in plant tissue in quantities measured in parts per million, ranging from 5 to 200 ppm, or less than 0.02% dry weight.[

Macronutrients (Primary N, P, K)Microbial inoculant

Microbial inoculants also known as soil inoculants are agricultural amendments that use beneficial endophytes (microbes) and earthworms to promote plant health. 

Many of the microbes involved form symbiotic relationships with earthworms where both parties benefit (mutualism). While microbial inoculants are applied to improve plant nutrition, they can also be used to promote plant growth by stimulating plant hormone production and auxin production as well as insect repellant protection.

Endophytes may benefit host plants by preventing pathogenic organisms from colonizing them. Extensive colonization of the plant tissue by endophytes creates a "barrier effect", where the local endophytes outcompete and prevent pathogenic organisms from taking hold. Endophytes may also produce chemicals which inhibit the growth of competitors, including pathogenic organisms. Some bacterial endophytes have proven to increase plant growth.[2] The presence of fungal endophytes can cause higher rates of water loss in leaves. However, certain fungal endophytes help plants survive drought and heat.[3] Plant use of endophytic fungi in defense is a very common phenomenon, primarily involving the arbuscular mycorrhizal fungi.

Research into the benefits of inoculants in agriculture extends beyond their capacity as biofertilizers. Microbial inoculants can induce systemic acquired resistance (SAR) of crop species to several common crop diseases (provides resistance against pathogens). So far SAR has been demonstrated for powdery mildew (Blumeria graminis f. sp. hordei, Heitefuss, 2001), take-all (Gaeumannomyces graminis var. tritici, Khaosaad et al., 2007), leaf spot (Pseudomonas syringae, Ramos Solano et al., 2008) and root rot (Fusariumculmorum, Waller et al. 200

Biological Fertilizers

Humates - Humic and fulvic acids (fulvic acids are humic acids of lower molecular weight and higher oxygen content than other humic acids) are commonly used as a soil supplement in agriculture

Primary Minerals


Further information: Nitrogen cycle

Nitrogen is an essential component of all proteins. Nitrogen deficiency most often results in stunted growth, slow growth, and chlorosis. Nitrogen deficient plants will also exhibit a purple appearance on the stems, petioles and underside of leaves from an accumulation of anthocyanin pigments.[4] Most of the nitrogen taken up by plants is from the soil in the forms of NO3, although in acid environments such as boreal forests where nitrification is less likely to occur, ammonium NH4+ is more likely to be the dominating source of nitrogen.[6] Amino acids and proteins can only be built from NH4+ so NO3 must be reduced. Under many agricultural settings, nitrogen is the limiting nutrient of high growth. Some plants require more nitrogen than others, such as corn (Zea mays). Because nitrogen is mobile, the older leaves exhibit chlorosis and necrosis earlier than the younger leaves. Soluble forms of nitrogen are transported as amines and amides[4] plants is characterized by an intense green coloration in leaves. If the plant is experiencing high phosphorus deficiencies the leaves may become denatured and show signs of necrosis. Occasionally the leaves may appear purple from an accumulation ofanthocyanin. Because phosphorus is a mobile nutrient, older leaves will show the first signs of deficiency5).


Phosphorus is important in plant bioenergetics. As a component of ATP, phosphorus is needed for the conversion of light energy to chemical energy (ATP) during photosynthesis. Phosphorus can also be used to modify the activity of various enzymes by phosphorylation, and can be used for cell signaling. Since ATP can be used for the biosynthesis of many plant biomolecules, phosphorus is important for plant growth and flower/seed formation. Phosphate esters make up DNA, RNA, and phospholipids. Most common in the form of polyprotic phosphoric acid (H3PO4) in soil, but it is taken up most readily in the form of H2PO4. Phosphorus is limited in most soils because it is released very slowly from insoluble phosphates. Under most environmental conditions it is the limiting element because of its small concentration in soil and high demand by plants and microorganisms. Plants can increase phosphorus uptake by a mutualism with mycorrhiza.[4] A Phosphorus deficiency in


It is useful to apply a high phosphorus content fertilizer, such as bone meal, to perennials to help with successful root formation.[4]


Potassium regulates the opening and closing of the stomata by a potassium ion pump. Since stomata are important in water regulation, potassium reduces water loss from the leaves and increases drought tolerance. Potassium deficiency may cause necrosis or interveinal chlorosis. K+ is highly mobile and can aid in balancing the anion charges within the plant. It also has high solubility in water and leaches out of soils that rocky or sandy that can result in potassium deficiency. It serves as an activator of enzymes used in photosynthesis and respiration[4] Potassium is used to build cellulose and aids in photosynthesis by the formation of a chlorophyll precursor. Potassium deficiency may result in higher risk of pathogens, wilting, chlorosis, brown spotting, and higher chances of damage from frost and heat.

Macronutrients (secondary and tertiary)


Sulphur is a structural component of some amino acids and vitamins, and is essential in the manufacturing of chloroplasts. Sulphur is also found in the Iron Sulphur complexes of the electron transport chains in photosynthesis. It is immobile and deficiency therefore affects younger tissues first. Symptoms of deficiency include yellowing of leaves and stunted growth.


Calcium regulates transport of other nutrients into the plant and is also involved in the activation of certain plant enzymes. Calcium deficiency results in stunting. This nutrient is involved in photosynthesis and plant structure.[7][8] Blossom end rot is also a result of inadequate calcium.[7]


Main article: Magnesium in biological systems

Magnesium is an important part of chlorophyll, a critical plant pigment important in photosynthesis. It is important in the production of ATP through its role as an enzyme cofactor.Magnesium deficiency can result in interveinal chlorosis.


In plants, silicon strengthens cell walls, improving plant strength, health, and productivity.[9] Other benefits of silicon to plants include improved drought and frost resistance, decreased lodging potential and boosting the plant's natural pest and disease fighting systems.[10] Silicon has also been shown to improve plant vigor and physiology by improving root mass and density, and increasing above ground plant biomass and crop yields.[9] Although not considered an essential element for plant growth and development (except for specific plant species - sugarcane and members of the horsetail family),[11] silicon is considered a beneficial element in many countries throughout the world[12] due to its many benefits to numerous plant species when under abiotic or biotic stresses.[13] Silicon is currently under consideration by the Association of American Plant Food Control Officials (AAPFCO) for elevation to the status of a "plant beneficial substance."[14][15]

Silicon is the second most abundant element in earth’s crust. Higher plants differ characteristically in their capacity to take up silicon. Depending on their SiO2 content they can be divided into three major groups:

  • Wetland graminae-wetland rice, horse tail (10-15%)
  • Dryland graminae-sugar cane, most of the cereal species and few dicotyledons species (1-3%)
  • Most of dicotyledons especially legumes (<0.5%)
  • The long distance transport of Si in plants is confined to the xylem. Its distribution within the shoot organ is therefore determined by transpiration rate in the organs
  • The epidermal cell walls are impregnated with a film layer of silicon and effective barrier against water loss, cuticular transpiration rate in the organs.

Si can stimulate growth and yield by several indirect actions. These include decreasing mutual shading by improving leaf erectness, decreasing susceptibility to lodging, preventing Mn and Fe toxicity.


Some elements are directly involved in plant metabolism (Arnon and Stout, 1939).[citation needed] However, this principle does not account for the so-called beneficial elements, whose presence, while not required, has clear positive effects on plant growth.

 Mineral elements which either stimulate growth but are not essential or which are essential only for certain plant species, or under given conditions, are usually defined as beneficial elements.


Iron is necessary for photosynthesis and is present as an enzyme cofactor in plants. Iron deficiency can result in interveinal chlorosis and necrosis. Iron is not the structural part of chlorophyll but very much essential for its synthesis. Copper deficiency can be responsible for promoting an iron deficiency.[16]


Molybdenum is a cofactor to enzymes important in building amino acids. Involved in Nitrogen metabolism. Mo is part of Nitrate reductase enzyme.


Boron is important for binding of pectins in the RGII region of the primary cell wall, secondary roles may be in sugar transport, cell division, and synthesizing certain enzymes.Boron deficiency causes necrosis in young leaves and stunting.


Copper is important for photosynthesis. Symptoms for copper deficiency include chlorosis. Involved in many enzyme processes. Necessary for proper photosythesis. Involved in the manufacture of lignin (cell walls). Involved in grain is also hard to find


Manganese is necessary for photosynthesis,[17] including the building of chloroplastsManganese deficiency may result in coloration abnormalities, such as discolored spots on the foliage.


Sodium is involved in the regeneration of phosphoenolpyruvate in CAM and C4 plants. It can also substitute for potassium in some circumstances.


  • Essential for C4 plants rather C3
  • Substitution of K by Na: Plants can be classified into four groups:
  1. Group A- a high proportion of K can be replaced by Na and stimulate the growth, which cannot be achieved by the application of K
  2. Group B-specific growth responses to Na are observed but they are much less distinct
  3. Group C-Only minor substitution is possible and Na has no effect
  4. Group D- No substitution is occurred
  • Stimulate the growth- increase leaf area, stomata, improve the water balance
  • Na functions in metabolism
    1. C4 metabolism
    2. Impair the conversion of pyruvate to phosphoenol-pyruva
    3. Reduce the photosystem II activity and ultrastructural changes in mesophyll chloroplast
    • Replacing K functions
    1. Internal osmoticum
    2. Stomatal function
    3. Photosynthesis
    4. Counteraction in long distance transport
    5. Enzyme activation
    • Improves the crop quality e.g. improve the taste of carrots by increasing sucrose


Zinc is required in a large number of enzymes and plays an essential role in DNA transcription. A typical symptom of zinc deficiency is the stunted growth of leaves, commonly known as "little leaf" and is caused by the oxidative degradation of the growth hormone auxin.


In higher plants,Nickel is absorbed by plants in the form of Ni+2 ion . Nickel is essential for activation of urease, an enzyme involved with nitrogen metabolism that is required to process urea. Without Nickel, toxic levels of urea accumulate, leading to the formation of necrotic lesions. In lower plants, Nickel activates several enzymes involved in a variety of processes, and can substitute for Zinc and Iron as a cofactor in some enzymes.[2]


Chlorine, as compounded chloride, is necessary for osmosis and ionic balance; it also plays a role in photosynthesis.


Cobalt has proven to be beneficial to at least some plants, but is essential in others, such as legumes where it is required for nitrogen fixation for the symbiotic relationship it has with nitrogen-fixing bacteria.  Sodium can replace potassium's regulation of stomatal opening and closing[4]

  1. The requirement of Co for N2 fixation in legumes and non-legumes have been documented clearly
  2. Protein synthesis of Rhizobium is impaired due to Co deficiency
  3. It is still not clear whether Co has direct effect on higher plant

Vanadium may be required by some plants, but at very low concentrations. It may also be substituting for molybdenumSelenium and sodium may also be beneficial.


 In humans, selenium is a trace element nutrient that functions as cofactor for reduction of antioxidant enzymes, such as glutathione peroxidases[65] and certain forms of thioredoxin reductase found in animals and some plants (this enzyme occurs in all living organisms, but not all forms of it in plants require selenium).

Selenium also plays a role in the functioning of the thyroid gland and in every cell that uses thyroid hormone, by participating as a cofactor for the three of the four known types of thyroid hormone deiodinases, which activate and then deactivate various thyroid hormones and their metabolites: the iodothyronine deiodinases are the subfamily of deiodinase enzymes that use selenium as the otherwise rare amino acid selenocysteine. (Only the deiodinase iodotyrosine deiodinase, which works on the last break-down products of thyroid hormone, does not use selenium).[66]

Selenium may inhibit Hashimoto's disease, in which the body's own thyroid cells are attacked as alien. A reduction of 21% on TPO antibodies was reported with the dietary intake of 0.2 mg of selenium.[67]

Selenium shows evidence of reducing the effects of mercury toxicity.[68

*It is therefore essential that selenium be part of the plant growing medium for human food production. Selenium is not present in many soils in the world and therefore not present in the foods they produce.

]Selenium is an essential micronutrient for animals consumed for food and is then passed up to humans. 



Molecular formula


Cellulose is an organic compound with the formula (C6H10O5)n, a polysaccharide consisting of a linear chain of several hundred to over ten thousand β(1→4) linked D-glucose units.[2][3]

Cellulose is the structural component of the primary cell wall of green plants, many forms of algae and the oomycetes. Some species of bacteria secrete it to form biofilms. Cellulose is the most common organic compound on Earth. About 33% of all plant matter is cellulose (the cellulose content of cotton fiber is 90%, that of wood is 40–50% and that of dried hemp is approximately 75%).[4][5][6]

For industrial use, cellulose today is mainly obtained from wood pulp and cotton. Cellulose is mainly used to produce paperboardand paper; to a smaller extent it is converted into a wide variety of derivative products such as cellophane and rayon. Converting cellulose from energy crops into biofuels such as cellulosic ethanol is under investigation as an alternative fuel source.

Some animals, particularly ruminants and termites, can digest cellulose with the help of symbiotic micro-organisms that live in their guts. Humans can digest cellulose to some extent,[7][8] however it mainly acts as a hydrophilic bulking agent for feces and is often referred to as "dietary fiber".

Humic acid

Humic acid is a principal component of humic substances, which are the major organic constituents of soil (humus), peatcoal, many upland streamsdystrophic lakes, andocean water.[1] It is produced by biodegradation of dead organic matter. It is not a single acid; rather, it is a complex mixture of many different acids containing carboxyl andphenolate groups so that the mixture behaves functionally as a dibasic acid or, occasionally, as a tribasic acid. Humic acids can form complexes with ions that are commonly found in the environment creating humic colloids. Humic and fulvic acids (fulvic acids are humic acids of lower molecular weight and higher oxygen content than other humic acids) are commonly used as a soil supplement in agriculture, and less commonly as a human nutritional supplement. As a nutrition supplement, fulvic acid can be found in a liquid form as a component of mineral colloids. Fulvic acids are poly-electrolytes and are unique colloids that diffuse easily through membranes whereas all other colloids do not[citation needed]. According to the International Humic Substances Society all fulvic acids are colloids. Attempts to synthesize fulvic acids have failed[citation needed].

Formation and description

Humic substances are formed by the microbial degradation of dead plant matter, such as lignin. They are very resistant to further biodegradation. The precise properties and structure of a given sample depend on the water or soil source and the specific conditions of extraction. Nevertheless, the average properties of humic substances from different sources are remarkably similar.

Humic substances in soils and sediments can be divided into three main fractions: humic acids, fulvic acids, and humin. The humic and fulvic acids are extracted as a colloidal sol from soil and other solid phase sources into a strongly basic aqueous solution of sodium hydroxide or potassium hydroxide. Humic acids are precipitated from this solution by adjusting the pH to 1 with hydrochloric acid, leaving the fulvic acids in solution. This is the operational distinction between humic and fulvic acids. Humin is insoluble in dilute alkali. The alcohol-soluble portion of the humic fraction is, in general, named ulmic acid. So-called "gray humic acids" (GHA) are soluble in low-ionic-strength alkaline media; "brown humic acids" (BHA) are soluble in alkaline conditions independent of ionic strength; and fulvic acids (FA) are soluble independent of pH and ionic strength.[2]

Liquid chromatography and liquid-liquid extraction can be used to separate the components that make up a humic substance. Substances identified include mono-, di-, and tri-hydroxy acidsfatty acidsdicarboxylic acids, linear alcohols, phenolic acids, and terpenoids.[3]