Editing Plant nutrition

{{Short description|Study of the chemical elements and compounds necessary for normal plant life}}
[[File:NRCSMO02023 - Missouri (4769)(NRCS Photo Gallery).jpg|thumb|upright=1.5|Three [[soil scientist]]s examining a [[farm land]] sample]]
'''Plant nutrition''' is the study of the [[chemical element]]s and [[Chemical compound|compounds]] necessary for plant growth and reproduction, plant metabolism and their external supply. In its absence the plant is unable to complete a normal life cycle, or that the element is part of some essential plant constituent or [[metabolite]]. This is in accordance with [[Justus von Liebig|Justus von Liebig's]] [[Liebig's law of the minimum|law of the minimum]].<ref name="Epstein1972" /> The total essential plant nutrients include seventeen different elements: [[carbon]], [[oxygen]] and [[hydrogen]] which are absorbed from the air, whereas other nutrients including [[nitrogen]] are typically obtained from the soil (exceptions include some [[parasitic plant|parasitic]] or [[carnivorous plant]]s).

Plants must obtain the following mineral nutrients from their growing medium:<ref>{{Cite web |title=Macronutrients and Micronutrients |url=https://soilsfacstaff.cals.wisc.edu/facstaff/barak/soilscience326/macronut.htm |access-date=2022-07-15 |website=soilsfacstaff.cals.wisc.edu}}</ref>
* The [[macronutrients]]: [[nitrogen]] (N), [[phosphorus]] (P), [[potassium]] (K), [[calcium]] (Ca), [[sulfur]] (S), [[magnesium]] (Mg), [[carbon]] (C), [[hydrogen]] (H), [[oxygen]] (O)
* The [[micronutrient]]s (or trace minerals): [[iron]] (Fe), [[boron]] (B), [[chlorine]] (Cl), [[manganese]] (Mn), [[zinc]] (Zn), [[copper]] (Cu), [[molybdenum]] (Mo), [[nickel]] (Ni)

These elements stay beneath soil as [[Salt (chemistry)|salts]], so plants absorb these elements as [[ions]]. The macronutrients are taken up in larger quantities; hydrogen, oxygen, nitrogen and carbon contribute to over 95% of a plant's entire biomass on a dry matter weight basis. Micronutrients are present in plant tissue in quantities measured in parts per million, ranging from 0.1<ref name="Marschner2012" /> to 200&nbsp;ppm, or less than 0.02% dry weight.<ref name=aesl />

Most [[soil]] conditions across the world can provide plants adapted to that climate and soil with sufficient nutrition for a complete life cycle, without the addition of nutrients as [[fertilizer]]. However, if the soil is cropped it is necessary to artificially modify [[soil fertility]] through the addition of [[fertilizer]] to promote vigorous growth and increase or sustain yield. This is done because, even with adequate water and light, [[Physiological plant disorders#Nutrient deficiencies|nutrient deficiency]] can limit growth and crop yield.

==History==

[[Carbon]], [[hydrogen]] and [[oxygen]] are the basic nutrients plants receive from air and water. [[Justus von Liebig]] proved in 1840 that plants needed [[nitrogen]], [[potassium]] and [[phosphorus]]. [[Liebig's law of the minimum]] states that a plant's growth is limited by nutrient deficiency.<ref>{{cite web |title=Liebig's law of the minimum |website=Oxford Reference |url=https://www.oxfordreference.com/view/10.1093/oi/authority.20110803100104700}}</ref> Plant cultivation in media other than soil was used by Arnon and Stout in 1939 to show that [[molybdenum]] was essential to [[tomato]] growth.{{Citation needed|date=May 2023}}

==Processes==
Plants take up [[Mineral (nutrient)|essential elements]] from the soil through their roots and from the air through their leaves. Nutrient uptake in the soil is achieved by [[Ion exchange|cation exchange]], wherein [[root hair]]s pump hydrogen ions (H<sup>+</sup>) into the soil through [[proton pump]]s. These hydrogen ions displace cations attached to negatively charged soil particles so that the cations are available for uptake by the root. In the leaves, [[stoma]]ta open to take in carbon dioxide and expel oxygen. The carbon dioxide molecules are used as the carbon source in [[photosynthesis]].

The [[root]], especially the root hair, a unique cell, is the essential organ for the uptake of nutrients. The structure and architecture of the root can alter the rate of nutrient uptake. Nutrient ions are transported to the center of the root, the [[stele (biology)|stele]], in order for the nutrients to reach the conducting tissues, xylem and phloem.<ref name="HunerHopkins2009"/> The [[Casparian strip]], a cell wall outside the stele but in the root, prevents passive flow of water and nutrients, helping to regulate the uptake of nutrients and water. [[Xylem]] moves water and mineral ions in the plant and [[phloem]] accounts for organic molecule transportation. [[Water potential]] plays a key role in a plant's nutrient uptake. If the water potential is more negative in the plant than the surrounding soils, the nutrients will move from the region of higher solute concentration—in the soil—to the area of lower solute concentration - in the plant.

There are three fundamental ways plants uptake nutrients through the root:
# [[Molecular diffusion|Simple diffusion]] occurs when a nonpolar molecule, such as O<sub>2</sub>, CO<sub>2</sub>, and NH<sub>3</sub> follows a concentration gradient, moving passively through the cell lipid bilayer membrane without the use of transport proteins.
# [[Facilitated diffusion]] is the rapid movement of solutes or ions following a concentration gradient, facilitated by transport proteins.
# [[Active transport]] is the uptake by cells of ions or molecules against a concentration gradient; this requires an energy source, usually ATP, to power molecular pumps that move the ions or molecules through the membrane.

Nutrients can be moved in plants to where they are most needed. For example, a plant will try to supply more nutrients to its younger leaves than to its older ones. When nutrients are mobile in the plant, symptoms of any deficiency become apparent first on the older leaves. However, not all nutrients are equally mobile. Nitrogen, phosphorus, and potassium are mobile nutrients while the others have varying degrees of mobility. When a less-mobile nutrient is deficient, the younger leaves suffer because the nutrient does not move up to them but stays in the older leaves.  This phenomenon is helpful in determining which nutrients a plant may be lacking.

Many plants engage in [[symbiosis]] with microorganisms.  Two important types of these relationship are
# with bacteria such as [[rhizobia]], that carry out [[biological nitrogen fixation]], in which atmospheric [[nitrogen]] (N<sub>2</sub>) is converted into [[ammonium]] (NH{{su|b=4|p=+}}); and
# with [[mycorrhiza]]l [[Fungus|fungi]], which through their association with the plant roots help to create a larger effective root surface area. Both of these mutualistic relationships enhance nutrient uptake.<ref name="HunerHopkins2009"/>

The Earth's atmosphere contains over 78 percent nitrogen. Plants called legumes, including the agricultural crops alfalfa and soybeans, widely grown by farmers, harbour nitrogen-fixing bacteria that can convert atmospheric nitrogen into nitrogen the plant can use. Plants not classified as legumes such as wheat, corn and rice rely on nitrogen compounds present in the soil to support their growth. These can be supplied by [[Mineralization (soil science)|mineralization]] of [[soil organic matter]] or added plant residues, nitrogen fixing bacteria, animal waste, through the breaking of triple bonded N<sub>2</sub> molecules by lightning strikes or through the application of [[fertilizer]]s.

==Functions of nutrients==
{{Further|Soil#Nutrients}}

At least 17 elements are known to be essential nutrients for plants. In relatively large amounts, the soil supplies nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur; these are often called the [[Nutrient|macronutrients]]. In relatively small amounts, the [[soil]] supplies iron, manganese, boron, molybdenum, copper, zinc, chlorine, and cobalt, the so-called [[Nutrient|micronutrients]]. Nutrients must be available not only in sufficient amounts but also in appropriate ratios.

Plant nutrition is a difficult subject to understand completely, partially because of the variation between different plants and even between different species or individuals of a given clone. Elements present at low levels may cause deficiency symptoms, and toxicity is possible at levels that are too high. Furthermore, deficiency of one element may present as symptoms of toxicity from another element, and vice versa. An abundance of one nutrient may cause a deficiency of another nutrient. For example, K<sup>+</sup> uptake can be influenced by the amount of NH{{su|b=4|p=+}} available.<ref name="HunerHopkins2009"/>

Nitrogen is plentiful in the Earth's atmosphere, and a number of commercially-important agricultural plants engage in [[nitrogen fixation]] (conversion of atmospheric nitrogen to a biologically useful form). However, plants mostly receive their nitrogen through the soil, where it is already converted in biological useful form. This is important because the nitrogen in the atmosphere is too large for the plant to consume, and takes a lot of energy to convert into smaller forms. These include soybeans, edible beans and peas as well as clovers and alfalfa used primarily for feeding livestock.  Plants such as the commercially-important corn, wheat, oats, barley and rice require nitrogen compounds to be present in the soil in which they grow.

Carbon and oxygen are absorbed from the air while other nutrients are absorbed from the soil. [[Plant|Green plants]] ordinarily obtain their carbohydrate supply from the carbon dioxide in the air by the process of [[photosynthesis]]. Each of these nutrients is used for a different essential function.<ref name=Taiz2002 />

=== Basic nutrients ===

The basic nutrients are derived from air and water.<ref>{{cite book |last1=Mia |first1=M.A. Baset |title=Nutrition of Crop lants |publisher=Nova Science Publishers |page=2}}</ref>

====Carbon====

[[Carbon]] forms the backbone of most plant [[biomolecule]]s, including proteins, [[starch]]es and [[cellulose]]. [[Carbon fixation| Carbon is fixed]] through [[photosynthesis]]; this converts [[carbon dioxide]] from the air into [[carbohydrate]]s which are used to store and transport energy within the plant.

====Hydrogen====

[[Hydrogen]] is necessary for building sugars and building the plant. It is obtained almost entirely from water. Hydrogen ions are imperative for a proton gradient to help drive the electron transport chain in photosynthesis and for respiration.<ref name="HunerHopkins2009"/>

====Oxygen====

[[Oxygen]] is a component of many organic and inorganic molecules within the plant, and is acquired in many forms. These include: [[Dioxygen|O<sub>2</sub>]] and [[Carbon dioxide|CO<sub>2</sub>]] (mainly from the air via leaves) and [[Water|H<sub>2</sub>O]], [[Nitrate|NO{{su|b=3|p=−}}]], [[Dihydrogen phosphate|H<sub>2</sub>PO{{su|b=4|p=−}}]] and [[Sulfate|SO{{su|b=4|p=2−}}]] (mainly from the soil water via roots). Plants produce oxygen gas (O<sub>2</sub>) along with [[glucose]] during [[photosynthesis]] but then require O<sub>2</sub> to undergo aerobic [[cellular respiration]] and break down this glucose to produce [[Adenosine triphosphate|ATP]].

===Macronutrients (primary)===
{{Further|Microbial inoculant}}

====Nitrogen====
{{Further|Nitrogen cycle}}

[[Nitrogen]] is a major constituent of several of the most important plant substances. For example, nitrogen compounds comprise 40% to 50% of the dry matter of [[protoplasm]], and it is a constituent of [[amino acid]]s, the building blocks of [[protein]]s.<ref name="swan2"/> It is also an essential constituent of [[chlorophyll]].<ref name="Roy2006Chapter3" /> In many agricultural settings, nitrogen is the limiting nutrient for rapid growth.

====Phosphorus====
{{Further|Phosphorus cycle}}

Like nitrogen, [[phosphorus]] is involved with many vital plant processes. Within a plant, it is present mainly as a structural component of the [[nucleic acid]]s: [[DNA|deoxyribonucleic acid]] (DNA) and [[RNA|ribonucleic acid]] (RNA), as well as a constituent of fatty [[phospholipid]]s, that are important in membrane development and function. It is present in both organic and inorganic forms, both of which are readily translocated within the plant. All energy transfers in the cell are critically dependent on phosphorus.  As with all living things, phosphorus is part of the [[Adenosine triphosphate]] (ATP), which is of immediate use in all processes that require energy with the cells. Phosphorus can also be used to modify the activity of various enzymes by [[phosphorylation]], and is used for [[cell signaling]]. Phosphorus is concentrated at the most actively growing points of a plant and stored within seeds in anticipation of their germination.

====Potassium====
{{Further|Potassium channel}}

Unlike other major elements, [[potassium]] does not enter into the composition of any of the important plant constituents involved in metabolism,<ref name="swan2" /> but it does occur in all parts of plants in substantial amounts. It is essential for enzyme activity including enzymes involved in primary metabolism. It plays a role in [[turgor pressure|turgor]] regulation, effecting the functioning of the stomata and cell volume growth.<ref name=sustr>{{cite journal |vauthors=Sustr M, Soukup A, Tylova E |title=Potassium in Root Growth and Development |date=2019 |journal=Plants |volume=8 |issue=10 |page=435 |doi=10.3390/plants8100435 |pmid=31652570 |pmc=6843428 |doi-access=free }}</ref>

It seems to be of particular importance in leaves and at growing points. Potassium is outstanding among the nutrient elements for its mobility and solubility within plant tissues.

Processes involving potassium include the formation of [[carbohydrate]]s and [[protein]]s, the regulation of internal plant moisture, as a catalyst and condensing agent of complex substances, as an accelerator of enzyme action, and as contributor to [[photosynthesis]], especially under low light intensity. Potassium regulates the opening and closing of the [[stomata]] by a potassium ion pump. Since stomata are important in water regulation, potassium regulates water loss from the leaves and increases [[drought]] tolerance. Potassium serves as an activator of enzymes used in photosynthesis and respiration.<ref name="HunerHopkins2009"/> Potassium is used to build cellulose and aids in photosynthesis by the formation of a chlorophyll precursor. The potassium ion (K<sup>+</sup>) is highly mobile and can aid in balancing the anion (negative) charges within the plant. A relationship between potassium nutrition and cold resistance has been found in several tree species, including two species of spruce.<ref name="sato"/> Potassium helps in fruit coloration, shape and also increases its [[brix]]. Hence, quality fruits are produced in potassium-rich soils.

Research has linked K<sup>+</sup> transport with auxin homeostasis, cell signaling, cell expansion, membrane trafficking and phloem transport.<ref name=sustr/>

===Macronutrients (secondary and tertiary)===

====Sulfur====
[[Sulfur]] is a structural component of some amino acids (including [[cysteine]] and [[methionine]]) and vitamins, and is essential for [[chloroplast]] growth and function; it is found in the iron-sulfur complexes of the electron transport chains in photosynthesis. It is needed for N<sub>2</sub> fixation by legumes, and the conversion of nitrate into amino acids and then into protein.<ref>{{cite book|last1=Haneklaus|first1=Silvia|last2=Bloem|first2=Elke|last3=Schnug|first3=Ewald|last4=de Kok|first4=Luit J.|last5=Stulen|first5=Ineke|editor1-last=Barker|editor1-first=Allen V.|editor2-last=Pilbeam|editor2-first=David J.|title=Handbook of plant nutrition|date=2007|publisher=CRC Press|isbn=978-0-8247-5904-9|pages=183–238|chapter-url=https://books.google.com/books?id=ZWjLBQAAQBAJ&q=sulfur|access-date=12 June 2017|chapter=Sulfur}}</ref>

====Calcium====
[[Calcium]] in plants occurs chiefly in the [[Leaf|leaves]], with lower concentrations in seeds, fruits, and roots. A major function is as a constituent of cell walls. When coupled with certain acidic compounds of the jelly-like pectins of the middle lamella, calcium forms an insoluble salt. It is also intimately involved in [[meristem]]s, and is particularly important in root development, with roles in cell division, cell elongation, and the detoxification of hydrogen ions. Other functions attributed to calcium are: the neutralization of organic acids; inhibition of some potassium-activated ions; and a role in nitrogen absorption. A notable feature of calcium-deficient plants is a defective root system.<ref name="russ"/> Roots are usually affected before above-ground parts.<ref name="chap"/> [[Calcium deficiency (plant disorder)|Blossom end rot]] is also a result of inadequate calcium.<ref name="transport protein identified"/>

[[Calcium]] regulates transport of other nutrients into the plant and is also involved in the activation of certain plant enzymes. [[Calcium deficiency (plant disorder)|Calcium deficiency]] results in stunting. This nutrient is involved in photosynthesis and plant structure.<ref name="transport protein identified" /><ref name=new-light /> It is needed as a balancing [[cation]] for [[anions]] in the [[vacuole]] and as an [[Calcium signaling|intracellular messenger]] in the [[cytosol]].<ref name=White>{{cite journal |last1=White |first1=Philip J. |last2=Broadley |first2=Martin R. |title=Calcium in Plants |journal=Annals of Botany |date=2003 |volume=92 |issue=4 |pages=487–511 |doi=10.1093/aob/mcg164 |pmid=12933363 |pmc=4243668 |doi-access=free }}</ref>

====Magnesium====
{{Main|Magnesium in biology}}

The outstanding role of [[magnesium]] in plant nutrition is as a constituent of the [[chlorophyll]] molecule. As a carrier, it is also involved in numerous enzyme reactions as an effective activator, in which it is closely associated with energy-supplying [[phosphorus]] compounds.

=== Micro-nutrients ===

Plants are able sufficiently to accumulate most trace elements. Some plants are sensitive indicators of the chemical environment in which they grow (Dunn 1991),<ref name="dunn" /> and some plants have barrier mechanisms that exclude or limit the uptake of a particular element or ion species, e.g., alder twigs commonly accumulate molybdenum but not arsenic, whereas the reverse is true of spruce bark (Dunn 1991).<ref name="dunn" /> Otherwise, a plant can integrate the geochemical signature of the soil mass permeated by its root system together with the contained groundwaters. Sampling is facilitated by the tendency of many elements to accumulate in tissues at the plant's extremities. Some micronutrients can be applied as seed coatings.

====Iron====
[[Iron]] is necessary for photosynthesis and is present as an enzyme cofactor in plants. [[Iron deficiency (plant disorder)|Iron deficiency]] can result in interveinal [[chlorosis]] and [[necrosis]].
Iron is not a structural part of chlorophyll but very much essential for its synthesis. Copper deficiency can be responsible for promoting an iron deficiency.<ref name=Ruhr2012 />
It helps in the electron transport of plant.

As with other biological processes, the main useful form of iron is that of iron(II) due to its higher solubility in neutral pH. However, plants are also capable of using iron(III) via citric acid, using the photo-reduction of [[Iron(III) citrate|ferric citrate]].<ref name=jesus>{{cite journal|doi=10.1093/pcp/pcp170|title=Identification of a Tri-Iron(III), Tri-Citrate Complex in the Xylem Sap of Iron-Deficient Tomato Resupplied with Iron: New Insights into Plant Iron Long-Distance Transport|year=2010|last1=Rellán-Álvarez|first1=Rubén|last2=Giner-Martínez-Sierra|first2=Justo|last3=Orduna|first3=Jesús|last4=Orera|first4=Irene|last5=Rodríguez-Castrillón|first5=José Ángel|last6=García-Alonso|first6=José Ignacio|last7=Abadía|first7=Javier|last8=Álvarez-Fernández|first8=Ana|journal=Plant and Cell Physiology|volume=51|issue=1|pages=91–102|pmid=19942594|doi-access=free}}</ref> In the field, as with many other transitional metal elements, iron fertilizer is supplied as a [[chelate]].<ref>{{Cite web|url=https://www.canr.msu.edu/news/selecting_which_iron_chelate_to_use|title=Selecting which iron chelate to use|date=10 May 2007 }}</ref>

====Molybdenum====
[[Molybdenum]] is a cofactor to enzymes important in building amino acids and is involved in nitrogen metabolism. Molybdenum is part of the [[nitrate reductase]] enzyme (needed for the reduction of nitrate) and the [[nitrogenase]] enzyme (required for [[biological nitrogen fixation]]).<ref name="Roy2006Chapter3">{{cite book|last1=Roy|first1=R.N.|last2=Finck|first2=A.|last3=Blair|first3=G.J.|last4=Tandon|first4=H.L.S.|title=Plant nutrition for food security: a guide for integrated nutrient management|date=2006|publisher=Food and Agriculture Organization of the United Nations|location=Rome|isbn=978-92-5-105490-1|pages=25–42|chapter-url=ftp://ftp.fao.org/agl/agll/docs/fpnb16.pdf|access-date=20 June 2016|chapter=Chapter 3: Plant nutrients and basics of plant nutrition|archive-date=18 May 2017|archive-url=https://web.archive.org/web/20170518110814/ftp://ftp.fao.org/agl/agll/docs/fpnb16.pdf|url-status=bot: unknown}}</ref> Reduced productivity as a result of [[Molybdenum deficiency (plant disorder)|molybdenum deficiency]] is usually associated with the reduced activity of one or more of these enzymes.

====Boron====
Boron has many functions in a plant:<ref>{{Cite journal |last1=Shireen |first1=Fareeha |last2=Nawaz |first2=Muhammad |last3=Chen |first3=Chen |last4=Zhang |first4=Qikai |last5=Zheng |first5=Zuhua |last6=Sohail |first6=Hamza |last7=Sun |first7=Jingyu |last8=Cao |first8=Haishun |last9=Huang |first9=Yuan |last10=Bie |first10=Zhilong |date=2018-06-24 |title=Boron: Functions and Approaches to Enhance Its Availability in Plants for Sustainable Agriculture |journal=International Journal of Molecular Sciences |language=en |volume=19 |issue=7 |pages=1856 |doi=10.3390/ijms19071856 |pmid=29937514 |pmc=6073895 |issn=1422-0067|doi-access=free }}</ref> it affects flowering and fruiting, pollen germination, cell division, and active salt absorption. The metabolism of amino acids and proteins, carbohydrates, calcium, and water are strongly affected by boron. Many of those listed functions may be embodied by its function in moving the highly polar sugars through cell membranes by reducing their polarity and hence the energy needed to pass the sugar. If sugar cannot pass to the fastest growing parts rapidly enough, those parts die.

====Copper====
[[Copper]] is important for photosynthesis. Symptoms for copper deficiency include chlorosis. It is involved in many enzyme processes; necessary for proper photosynthesis; involved in the manufacture of lignin (cell walls) and involved in grain production. It is difficult to find in some soil conditions.

====Manganese====
[[Manganese]] is necessary for photosynthesis,<ref name=new-light /> including the building of [[chloroplast]]s. [[Manganese deficiency (plant)|Manganese deficiency]] may result in coloration abnormalities, such as discolored spots on the [[foliage]].

====Sodium====
[[Sodium]] is involved in the regeneration of [[Phosphoenolpyruvic acid|phosphoenolpyruvate]] in [[Crassulacean acid metabolism|CAM]] and [[C4 carbon fixation|C4]] plants. Sodium can potentially replace potassium's regulation of stomatal opening and closing.<ref name="HunerHopkins2009"/>

Essentiality of sodium:
* Essential for C4 plants rather C3
* Substitution of K by Na: Plants can be classified into four groups:
# 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
# Group B—specific growth responses to Na are observed but they are much less distinct
# Group C—Only minor substitution is possible and Na has no effect
# Group D—No substitution occurs
* Stimulate the growth—increase leaf area and stomata. Improves the water balance
* Na functions in metabolism
# C4 metabolism
# Impair the conversion of pyruvate to phosphoenol-pyruvate
# Reduce the photosystem II activity and ultrastructural changes in mesophyll chloroplast
* Replacing K functions
# Internal osmoticum
# Stomatal function
# Photosynthesis
# Counteraction in long distance transport
# Enzyme activation
* Improves the crop quality e.g. improves the taste of carrots by increasing sucrose

====Zinc====
[[Zinc]] is required in a large number of enzymes and plays an essential role in [[Transcription (biology)|DNA transcription]]. A typical symptom of [[Zinc deficiency (plant disorder)|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]].

====Nickel====
In [[vascular plant|vascular plants]], [[nickel]] is absorbed by plants in the form of Ni<sup>2+</sup> 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 [[non-vascular plants]], nickel activates several enzymes involved in a variety of processes, and can substitute for zinc and iron as a cofactor in some enzymes.<ref name="BarkerPilbeam2007" />

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

====Cobalt====
[[Cobalt]] has proven to be beneficial to at least some plants although it does not appear to be essential for most species.<ref name="BarkerPilbeam2015" /> It has, however, been shown to be essential for [[nitrogen fixation]] by the nitrogen-fixing bacteria associated with [[legumes]] and other plants.<ref name="BarkerPilbeam2015" />

====Silicon====
[[Silicon]] is not considered an essential element for plant growth and development. It is always found in abundance in the environment and hence if needed it is available. It is found in the structures of plants and improves the health of plants.<ref>{{Cite web|url=http://canadianwollastonite.com/soil-amendments/silicon-plant-health/|title=Soil Amendments: Silicon and plant health|website=canadianwollastonite.com|language=en-US|access-date=2017-04-20|archive-url=https://web.archive.org/web/20170421092532/http://canadianwollastonite.com/soil-amendments/silicon-plant-health/|archive-date=2017-04-21|url-status=dead}}</ref>

In plants, [[silicon]] has been shown in experiments to strengthen [[cell wall]]s, improve plant strength, health, and productivity.<ref name=PHC /> There have been studies showing evidence of silicon improving [[Drought tolerance|drought]] and [[frost resistance]], decreasing [[lodging (agriculture)|lodging]] potential and boosting the plant's natural pest and disease fighting systems.<ref name=Bangalore /> 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 yield]]s.<ref name=PHC />  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".<ref name=AAPFCO2006 /><ref name=presentation />

====Vanadium====
[[Vanadium]] may be required by some plants, but at very low concentrations. It may also be substituting for [[molybdenum]].

====Selenium====
[[Selenium]] is probably not essential for flowering plants, but it can be beneficial; it can stimulate plant growth, improve tolerance of oxidative stress, and increase resistance to pathogens and herbivory.<ref name="White2016" />

==Mobility==

===Mobile===
Nitrogen is transported via the xylem from the roots to the leaf canopy as nitrate ions, or in an organic form, such as amino acids or amides. Nitrogen can also be transported in the phloem sap as amides, amino acids and ureides; it is therefore mobile within the plant, and the older leaves exhibit chlorosis and necrosis earlier than the younger leaves.<ref name="HunerHopkins2009"/><ref name="Roy2006Chapter3" /> Because phosphorus is a mobile nutrient, older leaves will show the first signs of deficiency. Magnesium is very mobile in plants, and, like potassium, when [[Magnesium deficiency (plants)|deficient]] is translocated from older to younger tissues, so that signs of deficiency appear first on the oldest tissues and then spread progressively to younger tissues.

===Immobile===
Because calcium is [[phloem]] immobile, calcium deficiency can be seen in new growth. When developing tissues are forced to rely on the [[xylem]], calcium is supplied by [[transpiration]] only.

Boron is not relocatable in the plant via the [[phloem]]. It must be supplied to the growing parts via the [[xylem]]. Foliar sprays affect only those parts sprayed, which may be insufficient for the fastest growing parts, and is very temporary.{{citation needed|date=February 2021}}

In plants, sulfur cannot be mobilized from older leaves for new growth, so deficiency symptoms are seen in the youngest tissues first.<ref>{{cite web|title=Plant Nutrition|url=http://www.fao.org/ag/agp/agpc/doc/publicat/faobul4/faobul4/b402.htm|website=www.fao.org|access-date=12 June 2017|archive-date=30 June 2017|archive-url=https://web.archive.org/web/20170630081507/http://www.fao.org/ag/AGP/AGPC/doc/publicat/FAOBUL4/FAOBUL4/B402.htm|url-status=dead}}</ref> Symptoms of deficiency include yellowing of leaves and stunted growth.<ref>{{cite web|title=Diagnosing sulphur deficiency in cereals|url=https://www.agric.wa.gov.au/mycrop/diagnosing-sulphur-deficiency-cereals|website=www.agric.wa.gov.au|access-date=12 June 2017|language=en}}</ref>

==Nutrient deficiency==

===Symptoms===
The effect of a nutrient deficiency can vary from a subtle depression of growth rate to obvious stunting, deformity, discoloration, distress, and even death. Visual symptoms distinctive enough to be useful in identifying a deficiency are rare. Most deficiencies are multiple and moderate. However, while a deficiency is seldom that of a single nutrient, nitrogen is commonly the nutrient in shortest supply.

[[Chlorosis]] of foliage is not always due to mineral nutrient deficiency. Solarization can produce superficially similar effects, though mineral deficiency tends to cause premature defoliation, whereas solarization does not, nor does solarization depress nitrogen concentration.<ref name="ronco" />

===Macronutrients===
[[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.<ref name="HunerHopkins2009"/>

[[Phosphorus deficiency]] can produce symptoms similar to those of nitrogen deficiency,<ref name="black" /> characterized by an intense green coloration or reddening in leaves due to lack of chlorophyll. If the plant is experiencing high phosphorus deficiencies the leaves may become denatured and show signs of death. Occasionally the leaves may appear purple from an accumulation of [[anthocyanin]]. As noted by Russel:<ref name="russ" /> "Phosphate deficiency differs from nitrogen deficiency in being extremely difficult to diagnose, and crops can be suffering from extreme starvation without there being any obvious signs that lack of phosphate is the cause". Russell's observation applies to at least some [[Pinophyta|coniferous]] seedlings, but Benzian<ref name="benz1965"/> found that although response to phosphorus in very acid forest tree nurseries in England was consistently high, no species (including Sitka spruce) showed any visible symptom of deficiency other than a slight lack of lustre. Phosphorus levels have to be exceedingly low before visible symptoms appear in such seedlings. In sand culture at 0 ppm phosphorus, white spruce seedlings were very small and tinted deep purple; at 0.62 ppm, only the smallest seedlings were deep purple; at 6.2 ppm, the seedlings were of good size and color.<ref name="swan4"/><ref name="swan5">Swan, H.S.D. 1962. The scientific use of fertilizers in forestry. p. 13-24 ''in'' La Fertilisation Forestière au Canada. Fonds de Recherches Forestières, Laval Univ., Quebec QC, Bull. 5</ref>

The root system is less effective without a continuous supply of calcium to newly developing cells. Even short term disruptions in calcium supply can disrupt biological functions and root function.<ref name=jakobsen/> A common symptom of calcium deficiency in leaves is the curling of the leaf towards the veins or center of the leaf. Many times this can also have a blackened appearance.<ref>{{Cite journal|last=Simon|first=E. W.|date=1978-01-01|title=The Symptoms of Calcium Deficiency in Plants|jstor=2431629|journal=The New Phytologist|volume=80|issue=1|pages=1–15|doi=10.1111/j.1469-8137.1978.tb02259.x|doi-access=free}}</ref> The tips of the leaves may appear burned and cracking may occur in some calcium deficient crops if they experience a sudden increase in humidity.<ref name=White/> Calcium deficiency may arise in tissues that are fed by the [[phloem]], causing blossom end rot in watermelons, peppers and tomatoes, empty peanut pods and bitter pits in apples. In enclosed tissues, calcium deficiency can cause celery black heart and "brown heart" in greens like [[escarole]].<ref>{{cite book |last=Thibodeau |first=Pierre Oliva |title=Lettuce Tipburn as Related to Calcium Nutrition |date=1968 |publisher=Cornell University  |page=36|url=https://books.google.com/books?id=rXJPAAAAYAAJ&q=brown+heart+lettuce+calcium}}</ref>

Researchers found that partial deficiencies of K or P did not change the [[fatty acid]] composition of [[phosphatidyl choline]] in ''[[Brassica napus L.]]'' plants. Calcium deficiency did, on the other hand, lead to a marked decline of [[polyunsaturated]] compounds that would be expected to have negative impacts for integrity of the plant [[membrane]], that could effect some properties like its permeability, and is needed for the [[ion]] uptake activity of the root membranes.<ref>{{cite book |title=Plant Roots and their Environment |year=1988 |publisher=Elsevier |page=25}}</ref>

[[Potassium deficiency (plants)|Potassium deficiency]] may cause necrosis or [[Chlorosis|interveinal chlorosis]]. Deficiency may result in higher risk of pathogens, wilting, chlorosis, brown spotting, and higher chances of damage from frost and heat. When potassium is moderately deficient, the effects first appear in the older tissues, and from there progress towards the growing points. Acute deficiency severely affects growing points, and die-back commonly occurs. Symptoms of potassium deficiency in white spruce include: browning and death of needles (chlorosis); reduced growth in height and diameter; impaired retention of needles; and reduced needle length.<ref name="heib"/>

===Micronutrients===
Mo deficiency is usually found on older growth. Fe, Mn and  Cu effect new growth, causing green or yellow veins, Zn ca effect old and new leaves, and B will be seem on terminal buds. A plant with [[Zinc deficiency (plant disorder)|zinc deficiency]] may have leaves on top of each other due to reduced internodal expansion.<ref>{{cite book |last=Alloway |first=Biran J. |title=Micronutrient Deficiencies in Global Crop Production |publisher=Springer |date=2008 |page=4}}</ref>

Zinc is the most widely deficient micronutrient for industrial crop cultivation, followed by boron. Acidifying N fertilizers create micro-sites around the [[wikt:granule|granule]] that keep micronutrient cations soluble for longer in alkaline soils, but high concentrations of P or C may negate these effects.

Boron deficiencies effecting seed yields and pollen fertility are common in [[laterite soil]]s.<ref>Alloway, 45.</ref> Boron is essential for the proper forming and strengthening of cell walls. Lack of boron results in short thick cells producing stunted fruiting bodies and roots. Deficiency results in the death of the terminal growing points and stunted growth.{{citation needed|date=February 2021}} Inadequate amounts of boron affect many agricultural crops, legume forage crops most strongly.{{citation needed|date=February 2021}} Boron deficiencies can be detected by analysis of plant material to apply a correction before the obvious symptoms appear, after which it is too late to prevent crop loss. Strawberries deficient in boron will produce lumpy fruit; apricots will not blossom or, if they do, will not fruit or will drop their fruit depending on the level of boron deficit. Broadcast of boron supplements is effective and long term; a foliar spray is immediate but must be repeated.{{citation needed|date=February 2021}}

==Toxicity==
{{cleanup section|reason=Might be better to merge with the "function" section, turning it into a list of nutrients similar to how [[Plant nutrients in soil]] is laid out.|date=March 2022}}
{{See also|Abiotic stress#In plants|Soil salinity}}
Boron concentration in soil water solution higher than one ppm is toxic to most plants. Toxic concentrations within plants are 10 to 50 ppm for small grains and 200 ppm in boron-tolerant crops such as sugar beets, rutabaga, cucumbers, and conifers. Toxic soil conditions are generally limited to arid regions or can be caused by underground borax deposits in contact with water or volcanic gases dissolved in percolating water.{{citation needed|date=February 2021}}

==Availability and uptake==

===Nitrogen fixation===
There is an abundant supply of nitrogen in the earth's atmosphere—N<sub>2</sub> gas comprises nearly 79% of air. However, N<sub>2</sub> is unavailable for use by most organisms because there is a triple bond between the two nitrogen atoms in the molecule,  making it almost inert. In order for nitrogen to be used for growth it must be [[Nitrogen fixation|"fixed"]] (combined) in the form of [[ammonium]] (NH{{su|b=4|p=+}}) or nitrate (NO{{su|b=3|p=−}}) ions. The weathering of rocks releases these ions so slowly that it has a negligible effect on the availability of fixed nitrogen. Therefore, nitrogen is often the limiting factor for growth and [[biomass]] production in all environments where there is a suitable climate and availability of water to support life.

[[Microorganism]]s have a central role in almost all aspects of nitrogen availability, and therefore for life support on earth. Some bacteria can convert N<sub>2</sub> into ammonia by the process termed ''[[nitrogen fixation]]''; these bacteria are either free-living or form [[Symbiosis|symbiotic]] associations with plants or other organisms (e.g., termites, protozoa), while other bacteria bring about transformations of [[ammonia]] to [[nitrate]], and of nitrate to N<sub>2</sub> or other nitrogen gases. Many [[bacteria]] and [[Fungus|fungi]] degrade organic matter, releasing fixed nitrogen for reuse by other organisms. All these processes contribute to the [[nitrogen cycle]].

Nitrogen enters the plant largely through the [[root]]s. A "pool" of soluble nitrogen accumulates. Its composition within a species varies widely depending on several factors, including day length, time of day, night temperatures, nutrient deficiencies, and nutrient imbalance. Short day length promotes [[asparagine]] formation, whereas glutamine is produced under long day regimes. Darkness favors protein breakdown accompanied by high asparagine accumulation. Night temperature modifies the effects due to night length, and soluble nitrogen tends to accumulate owing to retarded synthesis and breakdown of proteins. Low night temperature conserves [[glutamine]]; high night temperature increases accumulation of asparagine because of breakdown. Deficiency of K accentuates differences between long- and short-day plants. The pool of soluble nitrogen is much smaller than in well-nourished plants when N and P are deficient since uptake of nitrate and further reduction and conversion of N to organic forms is restricted more than is protein synthesis. Deficiencies of Ca, K, and S affect the conversion of organic N to protein more than uptake and reduction. The size of the pool of soluble N is no guide ''per se'' to growth rate, but the size of the pool in relation to total N might be a useful ratio in this regard. Nitrogen availability in the rooting medium also affects the size and structure of tracheids formed in the long lateral roots of white spruce (Krasowski and Owens 1999).<ref name="kras"/>

===Root environment===
====Mycorrhiza====
Phosphorus is most commonly found in the soil in the form of polyprotic phosphoric acid (H<sub>3</sub>PO<sub>4</sub>), but is taken up most readily in the form of H<sub>2</sub>PO{{su|b=4|p=−}}. Phosphorus is available to plants in limited quantities in most soils because it is released very slowly from insoluble phosphates and is rapidly fixed once again. Under most environmental conditions it is the element that limits growth because of this constriction and due to its high demand by plants and microorganisms. Plants can increase phosphorus uptake by a mutualism with mycorrhiza.<ref name="HunerHopkins2009"/> On some [[soil]]s, the phosphorus nutrition of some [[Pinophyta|conifers]], including the spruces, depends on the ability of [[mycorrhiza]]e to take up, and make soil phosphorus available to the tree, hitherto unobtainable to the non-mycorrhizal root. Seedling white spruce, greenhouse-grown in sand testing negative for phosphorus, were very small and purple for many months until spontaneous mycorrhizal inoculation, the effect of which was manifested by a greening of foliage and the development of vigorous shoot growth.

====Root temperature====
When [[soil]]-potassium levels are high, plants take up more potassium than needed for healthy growth. The term ''luxury consumption'' has been applied to this. Potassium intake increases with root temperature and depresses calcium uptake.<ref>{{cite journal |doi=10.1080/01904168009362774|title=Calcium uptake and distribution in plants|year=1980|last1=Wallace|first1=A.|last2=Mueller|first2=R. T.|journal=Journal of Plant Nutrition|volume=2|issue=1–2|pages=247–256|bibcode=1980JPlaN...2..247W }}</ref> Calcium to boron ratio must be maintained in a narrow range for normal plant growth. Lack of boron causes failure of calcium metabolism which produces hollow heart in beets and peanuts.{{citation needed|date=February 2021}}

===Nutrient interactions===
Calcium and magnesium inhibit the uptake of trace metals. Copper and zinc mutually reduce uptake of each other. Zinc also effects iron levels of plants. These interactions are dependent on species and growing conditions. For example, for clover, lettuce and red beet plants nearing toxic levels of zinc, copper and nickel, these three elements increased the toxicity of the others in a positive relationship. In barley positive interaction was observed between copper and zinc, while in French beans the positive interaction occurred between nickel and zinc. Other researchers have studied the synergistic and antagonistic effects of soil conditions on lead, zinc, cadmium and copper in radish plants to develop predictive indicators for uptake like [[soil pH]].<ref>{{cite book |last=Farago |first=Margaret E. |title=Plants and the Chemical Elements: Biochemistry, Uptake, Tolerance and Toxicity |publisher=VCH |page=38}}</ref>

Calcium absorption is increased by water-soluble phosphate fertilizers, and is used when potassium and [[potash]] fertilizers decrease the uptake of phosphorus, magnesium and calcium. For these reasons, imbalanced application of potassium fertilizers can markedly decrease crop yields.<ref name=jakobsen>{{cite journal |last=Jakobsen |first=Svend Tage |title=Interaction between Plant Nutrients |journal=Acta Agriculturae Scandinavica |volume=43 |issue=6 |pages=6–10 |date=1993}}</ref>

===Solubility and soil pH===
{{Main|Soil pH}}

[[Boron]] is available to plants over a range of pH, from 5.0 to 7.5. Boron is absorbed by plants in the form of the anion BO{{su|b=3|p=3−}}. It is available to plants in moderately soluble mineral forms of Ca, Mg and Na borates and the highly soluble form of organic compounds. It is mobile in the soil, hence, it is prone to leaching. Leaching removes substantial amounts of boron in sandy soil, but little in fine silt or clay soil. Boron's fixation to those minerals at high pH can render boron unavailable, while low pH frees the fixed boron, leaving it prone to leaching in wet climates. It precipitates with other minerals in the form of borax in which form it was first used over 400 years ago as a soil supplement. Decomposition of organic material causes boron to be deposited in the topmost soil layer. When soil dries it can cause a precipitous drop in the availability of boron to plants as the plants cannot draw nutrients from that desiccated layer. Hence, boron deficiency diseases appear in dry weather.{{citation needed|date=February 2021}}

Most of the nitrogen taken up by plants is from the soil in the forms of NO{{su|b=3|p=−}}, although in acid environments such as boreal forests where nitrification is less likely to occur, ammonium NH{{su|b=4|p=+}} is more likely to be the dominating source of nitrogen.<ref name=Lowenfels2011 /> Amino acids and proteins can only be built from NH{{su|b=4|p=+}}, so NO{{su|b=3|p=−}} must be reduced.

Fe and Mn become oxidized and are highly unavailable in acidic soils.{{citation needed|date=February 2021}}

==Measurements==

Nutrient status (mineral nutrient and trace element composition, also called ionome and nutrient profile) of plants are commonly portrayed by tissue elementary analysis. Interpretation of the results of such studies, however, has been controversial.<ref name="parent" /> During recent decades the nearly two-century-old "law of minimum" or "Liebig's law" (that states that plant growth is controlled not by the total amount of resources available, but by the scarcest resource) has been replaced by several mathematical approaches that use different models in order to take the interactions between the individual nutrients into account.{{citation needed|date=February 2021}}

Later developments in this field were based on the fact that the nutrient elements (and compounds) do not act independently from each other;<ref name="parent" /> Baxter, 2015,<ref name="baxter">{{Cite journal |doi=10.1093/jxb/erv040|pmid=25711709|pmc=4986723|title=Should we treat the ionome as a combination of individual elements, or should we be deriving novel combined traits?|journal=Journal of Experimental Botany|volume=66|issue=8|pages=2127–2131|year=2015|last1=Baxter|first1=Ivan}}</ref> because there may be direct chemical interactions between them or they may influence each other's uptake, translocation, and biological action via a number of mechanisms<ref name="parent">{{Cite journal |doi=10.3389/fpls.2013.00039|pmid=23526060|pmc=3605521|title=The Plant Ionome Revisited by the Nutrient Balance Concept|journal=Frontiers in Plant Science|volume=4|pages=39|year=2013|last1=Parent|first1=Serge-Étienne|last2=Parent|first2=Léon Etienne|last3=Egozcue|first3=Juan José|last4=Rozane|first4=Danilo-Eduardo|last5=Hernandes|first5=Amanda|last6=Lapointe|first6=Line|last7=Hébert-Gentile|first7=Valérie|last8=Naess|first8=Kristine|last9=Marchand|first9=Sébastien|last10=Lafond|first10=Jean|last11=Mattos|first11=Dirceu|last12=Barlow|first12=Philip|last13=Natale|first13=William|doi-access=free}}</ref> as exemplified{{how|date=August 2020}} for the case of ammonia.<ref name="bittsan">{{Cite journal |doi=10.1016/j.plantsci.2014.12.005|pmid=25576003|title=Overcoming ammonium toxicity|journal=Plant Science|volume=231|pages=184–190|year=2015|last1=Bittsánszky|first1=András|last2=Pilinszky|first2=Katalin|last3=Gyulai|first3=Gábor|last4=Komives|first4=Tamas}}</ref>

==Plant nutrition in agricultural systems==

===Fertilizers===
Boron is highly soluble in the form of borax or boric acid and is too easily leached from soil making these forms unsuitable for use as a fertilizer. Calcium borate is less soluble and can be made from [[Borax|sodium tetraborate]]. Boron is often applied to fields as a contaminant in other soil amendments but is not generally adequate to make up the rate of loss by cropping. The rates of application of borate to produce an adequate alfalfa crop range from 15 pounds per acre for a sandy-silt, acidic soil of low organic matter, to 60 pounds per acre for a soil with high organic matter, high cation exchange capacity and high pH. Application rates should be limited to a few pounds per acre in a test plot to determine if boron is needed generally. Otherwise, testing for boron levels in plant material is required to determine remedies. Excess boron can be removed by irrigation and assisted by application of elemental sulfur to lower the pH and increase boron solubility. Foliar sprays are used on fruit crop trees in soils of high alkalinity.{{citation needed|date=February 2021}}

Selenium is, however, an essential mineral element for animal (including human) nutrition and [[Selenium deficiency|selenium deficiencies]] are known to occur when food or animal feed is grown on selenium-deficient soils. The use of inorganic selenium fertilizers can increase selenium concentrations in edible crops and animal diets thereby improving animal health.<ref name="White2016" />

It is useful to apply a high phosphorus content fertilizer, such as bone meal, to perennials to help with successful root formation.<ref name="HunerHopkins2009"/>

===Hydroponics===
[[Hydroponics]] is a method for growing plants in a water-nutrient solution without using nutrient-rich soil or substrates. Researchers and home gardeners can grow their plants in a controlled environment. The most common artificial nutrient solution is the [[Hoagland solution]], developed by D. R. Hoagland and W. C. Snyder in 1933. The solution (known as ''A-Z solution'') consists of all the essential macro- and micronutrients in the correct proportions necessary for most plant growth.<ref name="HunerHopkins2009"/> An aerator is used to prevent an [[Anoxic waters|anoxic]] event or hypoxia. [[Hypoxia (environmental)|Hypoxia]] can affect the nutrient uptake of a plant because, without oxygen present, respiration becomes inhibited within the root cells. The [[nutrient film technique]] is a hydroponic technique in which the roots are not fully submerged. Incomplete submergence allows for adequate aeration of the roots, while a "film" thin layer of nutrient-rich water is pumped through the system to provide nutrients and water to the plant.

==See also==
{{portal|Plants}}
* [[Horticulture]]
* [[International Plant Nutrition Colloquium]]
* [[Nutrient pollution]]
* [[Photosynthesis]]
* [[Plant physiology]]
* [[Phytochemistry]]
* [[Plant hormone]]
* [[Resource recovery]]
* [[Soil]]

==References==

{{Reflist|refs=
<ref name="Epstein1972">{{cite book|author1=Emanuel Epstein|title=Mineral Nutrition of Plants: Principles and Perspectives|year=1972|publisher=New York, Wiley|isbn=9780471243403|url=https://archive.org/details/mineralnutrition00epst|url-access=registration}}</ref>
<ref name="BarkerPilbeam2007">{{cite book|author1=Allen V. Barker|author2=D. J. Pilbeam|title=Handbook of plant nutrition|url=https://books.google.com/books?id=ZWjLBQAAQBAJ|access-date=17 August 2010|year=2007|publisher=CRC Press|isbn=978-0-8247-5904-9}}</ref>
<ref name="BarkerPilbeam2015">{{cite book|last1=Barker|first1=AV|last2=Pilbeam|first2=DJ|title=Handbook of Plant Nutrition.|date=2015|publisher=CRC Press|isbn=9781439881972|edition=2nd|url=https://books.google.com/books?id=Ttw_CQAAQBAJ&q=cobalt&pg=PP1|access-date=5 June 2016}}</ref><ref name=aesl>{{cite web |url=http://aesl.ces.uga.edu/publications/plant/Nutrient.htm |title=Archived copy |access-date=2010-02-10 |url-status=dead |archive-url=https://web.archive.org/web/20100219114737/http://aesl.ces.uga.edu/publications/plant/Nutrient.htm |archive-date=2010-02-19 }} Retrieved Jan. 2010</ref>
<ref name="Marschner2012">{{cite book|editor1-last=Marschner|editor1-first=Petra|title=Marschner's mineral nutrition of higher plants|date=2012|publisher=Elsevier/Academic Press|location=Amsterdam|isbn=9780123849052|edition=3rd}}</ref>
<ref name="HunerHopkins2009">{{cite book|author1=Norman P. A. Huner|author2=William Hopkins|title=Introduction to Plant Physiology 4th Edition|publisher=John Wiley & Sons, Inc.|isbn=978-0-470-24766-2|chapter= 3 & 4|date=2008-11-07}}</ref>
<ref name=Taiz2002>Pages 68 and 69 Taiz and Zeiger Plant Physiology 3rd Edition 2002 {{ISBN|0-87893-823-0}}</ref>
<ref name="black">Black, C.A. 1957. Soil-plant relationships. New York, Wiley and Sons. 332 p.</ref>
<ref name="russ">Russell, E.W. 1961. Soil Conditions and Plant Growth, 9th ed. Longmans Green, London, U.K.. 688 p.</ref>
<ref name="benz1965">Benzian, B. 1965. Experiments on nutrition problems in forest nurseries. U.K. Forestry Commission, London, U.K., Bull. 37. 251 p. (Vol. I) and 265 p. (Vol II).</ref>
<ref name="swan4">Swan, H.S.D. 1960b. The mineral nutrition of Canadian pulpwood species. Phase II. Fertilizer pellet field trials. Progress Rep. 1. Pulp Pap. Res. Instit. Can., Montreal QC, Woodlands Res. Index No. 115, Inst. Project IR-W133, Res. Note No. 10. 6 p.</ref>
<ref name="heib">Heiberg, S.O.; White, D.P. 1951. Potassium deficiency of reforested pine and spruce stands in northern New York. Soil Sci. Soc. Amer. Proc. 15:369–376.</ref>
<ref name="sato">Sato, Y.; Muto, K. 1951. (Factors affecting cold resistance of tree seedlings. II. On the effect of potassium salts.) Hokkaido Univ., Coll. Agric., Coll. Exp. Forests, Res. Bull. 15:81–96.</ref>
<ref name="swan2">Swan, H.S.D. 1971a. Relationships between nutrient supply, growth and nutrient concentrations in the foliage of white and red spruce. Pulp Pap. Res. Inst. Can., Woodlands Pap. WR/34. 27 p.</ref>
<ref name=Lowenfels2011>{{cite book|last=Lowenfels, Lewis|first=Jeff, Wayne|title=Teaming with microbes|year=2011|isbn=978-1-60469-113-9|pages=49, 110|publisher=Timber Press }}</ref>
<ref name="kras">{{cite journal | last1 = Krasowski | first1 = M.J. | last2 = Owens | first2 = J.N. | year = 1999 | title = Tracheids in white spruce seedling's long lateral roots in response to nitrogen availability | doi = 10.1023/A:1004610513572 | journal = Plant and Soil | volume = 217 | issue = 1/2| pages = 215–228 | s2cid = 841104 }}</ref>
<ref name=new-light>(2012). New Light Shined on Photosynthesis. http://www.newswise.com/articles/new-light-shined-on-photosynthesis University of Arizona</ref>
<ref name="transport protein identified">University of Zurich (2011). Blossom end rot: Transport protein identified. http://phys.org/news/2011-11-blossom-protein.html</ref>
<ref name="chap">Chapman, H.D. (Ed.) 1966. Diagnostic Criteria for Plants and Soils. Univ. California, Office of Agric. Publ. 794 p.</ref>
<ref name=PHC>{{cite journal|title=Silicon nutrition in plants|journal=Plant Health Care, Inc.|date=12 December 2000|pages=1|url=http://excellerator.files.wordpress.com/2011/02/phc_silicon.pdf|archive-url=https://web.archive.org/web/20110419074023/http://excellerator.files.wordpress.com/2011/02/phc_silicon.pdf|url-status=dead|archive-date=19 April 2011|access-date=1 July 2011}}</ref>
<ref name=Bangalore>{{cite journal |last=Prakash |first=Dr. N. B. |title=Evaluation of the calcium silicate as a source of silicon in aerobic and wet rice |publisher<!-- was: journal, but this looks like a publisher -->=University of Agricultural Science Bangalore |year=2007 |pages=1}}</ref>
<ref name=AAPFCO2006>{{cite web|title=AAPFCO Board of Directors 2006 Mid-Year Meeting|url=https://docs.google.com/viewer?a=v&q=cache:iOI8KNDnLWIJ:www.aapfco.org/MY06BODAgenda.pdf+aapfco+silicon&hl=en&gl=us&pid=bl&srcid=ADGEESjMlF3h06OX6FdbTRJOEdaajE2qOt3w4NSERgyku4mg6N0CkbhDSWZE3P31RoNP-BDM4Td8YajxqeqPrnCNY1vt01pOAMfTO85N4j4AXUhwbR2q1Wba3orzcMj6Bpr0yk55P_GZ&sig=AHIEtbS2-zE_UrT_3T9_gqKrxD9us-1_bA|publisher=Association of American Plant Food Control Officials|access-date=18 July 2011}}</ref>
<ref name=presentation>{{cite web |last1=Miranda |first1=Stephen R. |first2=Bruce |last2=Barker |title=Silicon: Summary of Extraction Methods |url=https://docs.google.com/viewer?a=v&q=cache:SzfW40-2DDcJ:www.aapfco.org/AM09/LSC_Si_Methods_DC.ppt+aapfco+siicon&hl=en&gl=us&pid=bl&srcid=ADGEESj4Jo-RFFj54kb6Sun3ikgJW9DMHzRAuUS045YkFErzE5NaSA084KvIyRxJp0IVX5ktDhaPPqcYLRx2hVu6K5YVWj95h2kgvkvDLQLyrxcJXXD3tQ3P5YLJ7J5F8rRYzenxznHp&sig=AHIEtbSPNk7BtSIpiRnvNI1F-2jSLN5LYA|publisher= Harsco Minerals |date=August 4, 2009 |access-date=18 July 2011}}</ref>
<ref name="dunn">Dunn, C.E. 1991. Assessment of biogeochemical mapping at low sample density. Trans. Instit. Mining Metall., Vol. 100:B130–B133.</ref>
<ref name="Ruhr2012">{{Cite web |url=http://esciencenews.com/articles/2012/04/13/nutrient.and.toxin.all.once.how.plants.absorb.perfect.quantity.minerals |title=Nutrient and toxin all at once: How plants absorb the perfect quantity of minerals |date=April 12, 2012 |website=esciencenews.com |access-date=2019-03-12}}</ref>
<ref name="ronco">{{Cite journal |last=Ronco |first=F. |year=1970 |title=Chlorosis of planted Engelmann spruce seedlings unrelated to nitrogen content |journal=Can. J. Bot. |volume=48 |issue=5 |pages=851–853|doi=10.1139/b70-117 }}</ref>
<ref name="White2016">{{cite journal|last1=White|first1=Philip J.|title=Selenium accumulation by plants|journal=Annals of Botany|date=2016|volume=117|issue=2|pages=217–235|doi=10.1093/aob/mcv180|url= |pmc=4724052|pmid=26718221}}</ref>
|2}}

===Sources===

* {{cite book
 | last1 =Konrad | first1=Mengel
 | last2 =Kirkby | first2 = Ernest
 | last3 =Kosegarten | first3 = Harald
 | last4 =Appel | first4 = Thomas
 | title = Principles of Plant Nutrition
 | publisher = Kluwer Academic Publishers
 | edition = 5th
 | year =2001
 | url =https://books.google.com/books?id=ePhJuYcz4yUC&q=plant+nutrient&pg=PA1
 | isbn =978-1-4020-0008-9 }}

{{Plant nutrition}}
{{Hydroculture}}{{Botany}}{{Authority control}}

[[Category:Plant nutrition| ]]
[[Category:Botany|Nutrition]]
[[Category:Edaphology]]
[[Category:Biology and pharmacology of chemical elements]]