NUTRIENT GENERAL CHEMISTRY AND PLANT FUNCTION

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Chapter 2

• NUTRIENT GENERAL CHEMISTRY AND PLANT FUNCTION

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What nutrients do plants need?

• Plants require 16 nutrients each is a chemical
  element
• Plants do not require organic matter, enzymes or
  hormones as nutrients taken up from the soil.
• Plant requirements for these substances is met by
  the plants own manufacture of them.
• Except for carbon (C), hydrogen (H), oxygen (O),
  and boron (B) the nutrients are absorbed
  primarily as chemical ions from the soil
  solution.

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• CHOPKNS CaFe MgB Mn ClCuZn Mo
• A 17th Nutrient has been added.
• Sodium Na

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What makes these nutrients essential?

• Must satisfy three specific criteria
• 1. Plants cannot complete their life cycle
  without the element.
• 2. Deficiency symptoms for the element can be
  corrected only by supplying the element in
  question.
• 3. The element is directly involved in the
  nutrition of the plant, apart from its effect on
  chemical or physical properties of the soil.

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What affects the soil availability of these
nutrients?

• Most of the nutrients are absorbed as ions from
  the soil solution or the soil cation exchange
  complex.
• Understanding the general chemistry of the
  nutrient ions, as it relates to their
  concentration in the soil solution, is critical
  to developing an understanding of how to manage
  their availability to plants.
• What affects nutrient ion solubility?
• Solubility is strongly influenced by the charge
  of the ion.
• The first step to understanding solubility of
  nutrient ions and molecules is to know ionic and
  molecular charges. Help comes from identifying
  common ions, from group I, II and VII of the
  periodic table, that have only one standard
  valance in the soil environment.
• To know these standard ions is as important to
  basic chemistry as knowing multiplication
  tables is to basic mathematics.

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www.webelements.com
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• A positively-charged ion, which has fewer
  electrons than protons, is known as a cation
• A negatively charged ion, which has more
  electrons in its electron shells than it has
  protons in its nuclei, is known as an anion

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• Elements that have only one valance state in the
  soil environment.

WEB ELEMENTS
Oxidation number or oxidation state charge of an
atom that results when the electrons in a
covalent bond are assigned to the more
elctronegative atom
Ionic Bond electrostatic forces that exist
between ions of opposite charge (left side metals
combined with right side NM) Covalent Bond
sharing of electrons between two atoms (2
NM) Metallic Bond each metal atom is bonded to
several neighboring atoms (give rise to
electrical conductivity and luster)
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Ion/molecule Name Oxidation State NH3 ammonia -3 N
H4 ammonium -3 N2 diatomic N 0 N2O nitrous
oxide 1 NO nitric oxide 2 NO2- nitrite 3 NO3- n
itrate 5 H2S hydrogen sulfide -2 SO4 sulfate 6
N 5 electrons in the outer shell loses 5
electrons (5 oxidation state NO3) gains 3
electrons (-3 oxidation state NH3) O 6 electrons
in the outer shell is always being reduced (gains
2 electrons to fill the outer shell) H 1
electron in the outer shell N is losing electrons
to O because O is more electronegative N gains
electrons from H because H wants to give up
electrons
Reduction, Net Gain of ElectronsOxidation, Net
Loss of Electrons
8 is the Magical Number
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• oxidation state - the degree of oxidation of an
  atom or ion or molecule for simple atoms or ions
  the oxidation number is equal to the ionic
  charge "the oxidation number of hydrogen is 1
  and of oxygen is -2"
• The oxidation state or oxidation number is
  defined as the sum of negative and positive
  charges  in an atom , which indirectly indicates
  the number of electrons  it has accepted or
  donated.

Oxygen oxidation number -2Hydrogen
oxidation number 1Nitrogen oxidation
number 0 N Oxidation State H or O
NH3 Charge 0 3(1) 3 3-(0)) 3
-3 N gains 3 NO3 Charge -1 3(-2)
-6 -6- (-1)) -5 5 N loses 5NH4
Charge 1 4(1) 4 4 (1)) 3
-3 N gains 3
N is losing electrons to O because O is more
electronegative N gains electrons from H because
H wants to give up electrons
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Oxidation State

• Cr(OH)3, O has an oxidation number of -2 H has
  a state of 1
• So, the triple hydroxide  group has a charge of
  3(-2 1) -3. As the compound is neutral, Cr
  has to have a charge of 3.

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Using this information, we can determine the
charge of molecules or the oxidation state of
elements in a charged molecule Ex CO3-2, we
should be able to determine, by difference, that
the oxidation state of C is 4 (3-2-6) -2
showing 4 CaCl2 is an uncharged calcium
chloride molecule

• The chemical formula, name, and charge of each
  molecule should be carefully studied (memorized).
  Significance of each to soil fertility is
  presented and discussed in later chapters.

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General effect of ion charge on solubility

• Availability of nutrient ions to plants and the
  solubility of compounds they come from, or may
  react to form, can be discussed from the
  perspective of the general reaction

An Bm- ? ? AmBn
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• Reactant ions An and Bm- combine to form a
  compound (usually a solid) predicted by their
  electrical charges.
• The higher the charge of either the cation or
  anion, the greater is the tendency for the
  compound or solid to be formed.
• When the solid is easily formed, only small
  concentrations of the reactants are necessary
  for the reaction to take place. Because of this,
  the compound or solid that forms is also
  relatively insoluble (it will not easily dissolve
  in water), or it does not easily break apart
  (reaction to the left). Conversely, if the
  cation and anion are both single-charged, then
  the compound (solid) is not as easily formed, and
  if it does form, it is relatively soluble.

An Bm- ? ? AmBn
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Real life examples of charge-influenced
solubility

• A common compound that represents single charged
  ions is sodium chloride (NaCl, table salt), whose
  solubility is given by the equilibrium reaction,

An Bm- ? ? AmBn
Na Cl- ? ? NaCl
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Examples

• Common table salt is very soluble and easily
  dissolves in water. Once dissolved, the solid
  NaCl does not reform until the ions, Na Cl-,
  are present in high concentration.
• When water is lost from the solution by
  evaporation the solid finally reforms as NaCl
  precipitate.
• Iron oxide or rust, represents multiple charged
  ions forming a relatively insoluble material.
  When iron reacts with oxygen and water (a humid
  atmosphere), a very insoluble solid, rust or iron
  oxide, is formed

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How does all this relate to nutrient availability?

• With regard to solubility of inorganic compounds,
  we may expect that when both the cation and
  anion are single charged, the resulting compound
  is usually very soluble.
• Examples are compounds formed from the cations
  H, NH4, Na, K and the anions OH-, Cl-, NO3-,
  H2PO4-, and HCO3- (bicarbonate). Note that NH4,
  K, Cl-, NO3-, and H2PO4- are nutrient ions.
• Because monovalent ions are very soluble, when a
  monovalent cation reacts with OH- to form a
  base, the base is very strong (e.g. NaOH, KOH).
• Strong Acid Strong ElectrolyteStrong Base
  Weak Electrolyte
• Similarly, when a monovalent anion reacts with H
  to form an acid, the acid is a strong acid (e.g.
  HCl, HNO3). The monovalent molecules H2PO4-, and
  HCO3-, which are products of multi-charged ions
  that have already reacted with H, are
  exceptions.
• Except for H and OH-, whenever either the cation
  or anion is single charged and reacts with a
  multiple charged ion, the resulting compound is
  usually very soluble. Another exception to this
  rule is for F-, which reacts with Al to form
  insoluble AlF3, a reaction important to soil
  test extractants of P in acid soils

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Multiple charged ions

• Divalent cations Mg 2 , Ca2 , Mn2 , Fe2 ,
  Cu2 , Zn2
• Divalent anions SO42-, CO32- (carbonate), HPO42-,
  and MoO42-
• Trivalent cations Fe 3 and Al 3
• Trivalent anion PO43-
• When monovalent anions Cl- or NO3- react with any
  of the multi-charged cations Mg 2 , Ca2 , Mn2
  , Fe2 , Cu2 , Zn2 Fe 3 and Al 3 the solid
  compounds are all quite soluble.
• Similarly, when any of the monovalent cations
  NH4, Na, or K reacts with any of the
  multi-charged anions SO42-, CO32-, HPO42-,
  MoO42-, or PO43-, the solids are all quite
  soluble.
• If both the cation and anion are divalent, the
  resulting compound will be only sparingly
  soluble. An example is gypsum (CaSO42H2O).
• If one of the ions is divalent and the other is
  trivalent, the compound will be moderately
  insoluble. An example is tricalcium phosphate,
  Ca3(PO4)2.
• If both the anion and cation are trivalent, the
  compound is very insoluble. An example is iron
  (ferric) phosphate, FePO4

AlPO4 ?
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How can these general rules be simplified?

• Once charges of the ions in a compound are known,
  we can get some idea of the compound solubility
  by simply adding the charges.
• For example, if the sum of the anion and cation
  charges is 2, then the compound is very soluble
  (e.g. NaCl).
• As the sum of the charges increases, the
  solubility of the compound decreases.
• Whenever one of the ions is monovalent the
  compound is usually very soluble (e.g. KCl,
  CaCl2, and FeCl3 are all soluble even though the
  sum of charges is 2, 3, and 4, respectively).
• Many examples where these simple rules are a good
  predictor of solubility. The sum of charges in
  CaSO4 is 4, and it is less soluble than CaCl2.
• The sum of charges in Ca(H2PO4)2 is 3 (Ca 2 and
  H2PO4-) and it is more soluble than CaHPO4 where
  the sum of charges is 4 (Ca 2 and HPO42-).
  Similarly, Ca3(PO4)2 has a charge sum of 5 (Ca 2
  and PO43-) and is less soluble than CaHPO4.

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Relative solubility of compounds formed from the
reaction of anions (An-) and cations (Mn) of
different charges.
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Why are some nutrients mobile and some immobile
in the soil?

• With a general understanding of nutrient ion
  solubility, it is now easier to examine the
  relative nutrient mobility in soils.
• Bray Nutrient management is closely linked to
  how mobile the nutrients are in the soil.
• Relative mobility of nutrients in soils is
  governed primarily by
• inorganic solubility
• ionic charge
• ionic adsorption (e.g., cations on the soil
  cation exchange sites), and
• biological immobilization

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Are all highly soluble nutrients mobile in the
soil?

• Monovalent nutrient ions have a good chance of
  being mobile in soils.
• Monovalent anions, Cl- and NO3-, are mobile in
  the soil because they are not adsorbed on ion
  exchange sites.
• They have the wrong charge (-) for adsorption on
  cation exchange sites and they are too weakly
  charged, compared to SO4 -- for example, to be
  adsorbed on anion exchange sites.
• Furthermore, most soils have limited anion
  exchange capacity (tropical soils are an
  exception).
• Monovalent cation nutrients, K and NH4, are
  highly water soluble, but relatively immobile in
  soils because they are adsorbed on cation
  exchange sites. These nutrient ions become more
  mobile in sandy, low organic matter soils that
  have extremely low cation exchange capacity.
• Plants absorb B as the uncharged, undissociated,
  boric acid molecule (H3BO3). Since this form of
  B is highly water-soluble and has no charge, it
  is mobile in soils.

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Are all divalent and trivalent nutrient ions
immobile in the soil?

• Divalent and trivalent nutrient ions are immobile
  in soils (exception SO42-)
• In tropical soils, are enough anion exchange
  sites to provide significant adsorption of SO42-
  and cause it to be somewhat immobile. Although
  sulfate compounds, such as CaSO4 and MgSO4 are
  relatively insoluble, the equilibrium
  concentration of SO42- with these solid compounds
  is far greater than that needed for plant growth.
  Phosphate is immobile in soils because it tends
  to form insoluble compounds with Ca in neutral
  and calcareous soils and Al and Fe in acidic
  soils (described in more detail in the chapter on
  P). Molybdate (MoO4 --) reacts to from insoluble
  solids similar to the solid-forming reactions
  described for phosphate.
• The divalent cation nutrients, Ca 2 , Mg2 ,
  Cu2 , Mn2 , and Zn2 are adsorbed on cation
  exchange sites in soils, which prevents them from
  being mobile. In addition, when divalent and
  trivalent anions are present, these cations will
  react to form sparingly soluble and insoluble
  solids (e.g. Ca3(PO4)2).
• Iron absorption by plants involves both Fe2 and
  Fe3 .
• Both are immobile in soils.
• Reduced form is usually not present in
  significant amounts, but could be absorbed on
  cation exchange sites.
• Trivalent iron forms insoluble solid oxides
  (rust) that prevent the ion from being mobile.
• Reduced (Fe) Oxidized (Fe)gains electrons
  loss of electrons
• Ferrous Ferric

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What are the plant concentrations, functions and
deficiency symptoms of the essential nutrients?

• Plant concentration of nutrients is helpful in
  managing nutrients that are mobile in the soil.
• For these nutrients, the crop requirement can be
  estimated by multiplying yield times plant
  concentration.
• Nitrogen
• Nitrogen component of all amino acids
• part of all proteins and enzymes
• Plants contain from 1 to 5 N
• Wheat (2.35) Corn (1.18N) Soybeans (5.2N)
• Young legumes contain about 4 N (25 crude
  protein) and recently fertilized turf may contain
  5 N.
• Nitrogen is a structural component of many plant
  compounds including chlorophyll and DNA.
• Deficiencies of N are the most common, worldwide,
  of any of the nutrients.

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Nutrients are grouped according to crop removal.

• Primary (N, P, K).
• Removed in largest amount by crop.
• Most commonly deficient.
• Secondary.
• Removed in moderate amount by crop.
• Micro.
• Removed in minute amount by crop.

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What are the Primary Nutrients needed by all
crops
Range of total amount in soil. From Chemical
Equilibria in Soils. W.L.Lindsay, 1979. Wiley
Sons.
Nutrient
Nitrogen (N)
Potassium (K)
Phosphorus (P)
Soil (lb/a)
400 8,000
800 - 60,000
400 10,000
Crop (lb/a)
80
40
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Calculated for 2 ton crop yield (67 bushel
wheat).
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Secondary Nutrients Neededby all Crops
Range of total in soil. From Chemical
Equilibria in Soils. W.L.Lindsay, 1979. Wiley
Sons.
Nutrient
Calcium
Magnesium
Sulfur
Soil (lb/a)
14,000 1,000,000
1,200 - 12,000
60 20,000
Crop (lb/a)
16
8
6
Calculated for 2 ton crop yield (67 bushel
wheat).
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Micronutrients Needed by all Crops
Nutrient
Iron
Manganese
Copper
Zinc
Boron
Chlorine
Molybdenum
Soil (lb/a)
14,000 1,100,000
40 6,000
4 - 200
20 - 600
4 - 200
40 1,800
0.4 - 10
Crop (lb/a)
1
0.8
0.08
0.6
0.08
4
0.0008
Range of total in soils. From Chemical
Equilibria in Soils. W.L.Lindsay, 1979. Wiley
Sons.
Calculated for 2 ton crop yield (67 bushel
wheat).
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Nutrient take up is Crop spec.
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Review Nutrients Needed by all Crops
Primary
Nitrogen (N)
Potassium (K)
Phosphorus (P)
Secondary
Calcium (Ca)
Magnesium (Mg)
Sulfur (S)
Micro
Iron (Fe)
Zinc (Zn)
Manganese (Mn)
Copper (Cu)
Chlorine (Cl)
Boron (B)
Molybdenum (Mo)
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Nutrients not commonly found deficient in
Oklahoma crops.

• Calcium.
• Liming prevents Ca deficiency.
• Manganese.
• Copper.
• Molybdenum.

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Nutrients seldom found deficient in Oklahoma
crops.

• Magnesium.
• Sulfur.
• Iron.
• Zinc.
• Boron.
• Chlorine.

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Nutrients often Deficient in Oklahoma crops.

• Nitrogen (N).
• Legumes like soybeans and alfalfa get their N
  from microorganisms (rhizobium) that fix N from
  the atmosphere.
• Phosphorus (P).
• Potassium (K).

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Nitrogen

• Wherever non-legumes are grown in a high-yielding
  monoculture system, and the crop is removed in
  harvest as a part of the farming enterprise, N
  deficiencies occur within a few years. (Straw,
  Residues)
• Deficient plants are stunted
• Low protein content
• develop chlorosis (yellowing) at the tip,
  progressing along the mid-rib toward the base of
  the oldest leaf.

http//www.nue.okstate.edu/Spatial_N_Variability.h
tm
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Nitrogen

• If the deficiency persists, the oldest leaf
  becomes completely chlorotic, eventually dying,
  while the pattern of chlorosis begins developing
  in the next to oldest leaf. The pattern of
  chlorosis develops as N is translocated to newly
  developing tissue (N is mobile in plants).
  Nitrogen deficiency reduces yield and hastens
  maturity in many plants.

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Nitrogen Deficiency.

• Shows up as chlorosis (yellowing) at the tip of
  the oldest leaf.
• Progresses toward the base of the leaf along the
  midrib (corn).
• Chlorosis continues to the next oldest leaf,
  after the oldest leaf becomes almost completely
  chlorotic, if deficiency continues.

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Nitrogen Deficiency in Corn.
chlorosis (yellowing) at the tip of the oldest
leaf.
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Nitrogen Deficiency in Corn.
Chlorosis continues to the next oldest leaf
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Phosphorus

• The P content of plants ranges from about 0.1 to
  0.4 , and is thus about 1/10th the concentration
  of N in plants.
• Storage and transfer of energy as ADP (adenosine
  di-phosphate) and ATP (adenosine tri-phosphate).
  High-energy phosphate bonds (ester linkage of
  phosphate groups) are involved

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ATP

• Biochemical reaction illustrating the release of
  energy and primary orthophosphate when ATP is
  converted to ADP (R denotes adenosine).

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Phosphorus

• Plant symptoms of P deficiency include poor root
  and seed development, and a purple discoloration
  of oldest (lower) leaves. Purple discoloration
  at the base of plant stalks (corn) and leaf
  petioles (cotton) is sometimes a genetic trait
  that may be incorrectly diagnosed as P
  deficiency.

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Phosphorus Deficiency.
purple coloring and sometimes yellow on lower
(oldest) leaves.
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Phosphorus Deficiency.

• Deficiency in Oklahoma cultivated soils is
  related to historical use of P-fertilizers.
• P builds up in soils when high-P, low-N
  fertilizers are the only input.
• 10-20-10 and 18-46-0.

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Rate of P Applied

• So, we know that plants have 1/10 the amount of P
  as N
• If both N and P were deficient, would we apply
• 1/10 the amount of N
• 1/5 the amount of N
• 1/2 the amount of N
• Doesnt matter, Bray said so

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Potassium.

• The content of K in plants is almost as high as
  for N, ranging from about 1 to 5 . Potassium
  functions as a co-factor (stimulator) for several
  enzyme reactions and is involved in the
  regulation of water in plants by influencing
  turgor pressure of stomatal guard cells.
• Potassium is mobile in plants and the deficiency
  symptoms are similar to those for N, except the
  chlorosis progresses from the tip, along the leaf
  margins (instead of the midrib), toward the base
  of the oldest leaf.
• Leaf margins usually die soon after chlorosis
  develops, resulting in a condition referred to as
  firing or leaf burn. Deficiencies are related
  to soil parent material, fertilizer use and
  cropping histories.

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Potassium Deficiency.

• Common in crops grown in weathered soils
  developed under high rainfall.
• Symptoms are chlorosis at the tip of the oldest
  leaf (like N), that progresses toward the base
  along the leaf margins.

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Potassium Deficiency.

• Common in crops grown in weathered soils
  developed under high rainfall.

K Usually adequate
K Usually deficient
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Potassium Deficiency.

• Chlorosis at the tip of the oldest leaf
  progressing toward the base along the leaf
  margins (corn, alfalfa).

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Calcium and Magnesium

• Calcium deficiencies are rare, although the
  concentration of Ca is relatively high (0.5 ) in
  plants. The primary function is in the formation
  and differentiation of cells. Deficiency results
  in development of a gelatinous mass in the region
  of the apical meristem where new cells would
  normally form.

Chlorophyll, showing the importance of N (apex of
four pyrrole rings) and Mg (centrally coordinated
atom in the porphyrin type structure). R
indicates carbon-chain groups.
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Mg cont.

• Magnesium is present at about 0.2, or one-half
  the concentration of Ca in plant tissue.
• Soil Mg levels are considerably lower than for
  Ca, and Mg deficiency does occasionally occur.
• Magnesium functions as a co-factor for several
  enzyme reactions and is the centrally coordinated
  metal atom in the chlorophyll molecule
• Intermediately mobile in plants, leading to
  deficiency symptoms of interveinal chlorosis in
  lower leaves.
• Deficiencies may be expected in deep,
  well-drained soils developed under high rainfall
  that are managed to produce and remove high
  forage yields (Example?)

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Magnesium and Sulfur additions.

• Lime, especially dolomitic, adds Mg.
• Rainfall adds 6 lb/acre/yr of S.
• Like 120 lb of N (crop needs 1 lb S for every 20
  lb N).

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Magnesium Deficiency in Alfalfa.
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Magnesium and Sulfur deficiencies.

• Occur on deep, sandy, low organic matter soils in
  high rainfall regions with high yielding forage
  production.
• Storage capacity for Mg and S is low.
• Large annual removal of nutrients.

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Sulfur

• Sulfur is present in plant tissue in
  concentrations ranging from 0.1 to 0.2 , similar
  to that for Mg. The function of S in plants is
  similar to that for N, component of three amino
  acids, cystine, cysteine, and methionine, which
  are important in the structural changes and
  shapes of enzymes

Sulfur NCSU
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Sulfur Deficiency in Corn.
Overall light green color, worse on new leaves
during rapid growth.
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Sulfur Deficiency in Wheat.
Overall light green color, worse on new leaves
during rapid growth.
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Zinc Deficiency in Corn (Kansas).
Note short internodes (stunted plants).
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Zinc Deficiency in Cotton (Mississippi)
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Zinc deficiencies.

• Usually found in high pH, low organic matter
  soils, and sensitive crops.
• Pecans, corn, soybeans and cotton.
• Crop symptoms are shortened internodes and bronze
  coloring.

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Correcting Zinc Deficiency in Crops.

• Broadcast and incorporate 6 to 10 lb of Zn as
  zinc sulfate preplant.
• This rate should eliminate the deficiency for 3
  to 4 years as compared to 1 to 2 lb applied
  annually.
• Foliar apply low rate to pecans annually.

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Micronutrient cation elements

• Immobile in plants and function as co-factors in
  enzyme reactions (Mn and Zn) or
  oxidation-reduction reactions
• Deficiency symptoms are found on the newest
  leaves.
• For Fe deficiency, the symptoms are a dramatic
  interveinal chlorosis (yellowing) of the newest
  leaves.

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Iron deficiencies.

• Limited to high pH soils and sensitive crops.
• West-central and western Oklahoma.
• Grain sorghum, sorghum sudan, and wheat (also pin
  oak, blueberries and azaleas).
• Crop symptoms are chlorosis between veins of
  newest leaves

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Iron Deficiency in Corn.
Note yellowing (chlorosis) between veins.
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Iron Deficiency in Peanuts
Note yellowing (chlorosis) between veins of
newest leaves.
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Correcting and Minimizing Iron Deficiency in
Crops.

• Select tolerant varieties and crops.
• Incorporate several tons of rotted organic matter
  per acre of affected soil.
• Use a foliar spray of 1 Fe as iron sulfate.
• Usually will require repeat spraying and will not
  be economical.

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Molybdenum

• Plants require Mo at tissue concentrations of
  about 0.1 to 0.2 ppm. It functions in critical
  enzymes related to N metabolism nitrate
  reductase, which reduces nitrate to amino-N, and
  nitrogenase, which is required for N2 fixation by
  legumes.
• Deficiency symptoms are similar to that described
  for N deficiency. Molybdenum appears to be
  mobile in plants (translocated from old to new
  tissue). Deficiencies are rare and are
  associated with very acid soils and soils that
  have a high content of iron oxides.

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Boron

• Of the remaining micronutrients, B is the most
  commonly deficient. However, even its deficiency
  is somewhat rare and most common in regions of
  relatively high rainfall (gt 40 inches per year).
  
• It is found at tissue concentrations of about 20
  ppm and is believed to function in sugar
  translocation, although it is extremely immobile
  in plants. Deficiency symptoms include poor root
  and internal seed development (hollow heart in
  peanuts)

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Correcting Boron Deficiency in Crops.

• Apply ½ to 1 lb B according to soil test.
• May be applied as addition to N-P-K blend or
  foliar spray in-season.
• Excessive rates may kill crop.
• Applications may be needed each year.

BORAX
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Boron Deficiencies.

• Occasionally found in peanuts grown in sandy, low
  organic matter soils.
• Responsible for hollow heart.

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Chlorine

• Since its discovery as an essential plant
  nutrient in the mid 1950s, the function of Cl in
  plants has been somewhat of a mystery.
• Required in plant tissue at concentrations of
  only about 100 ppm (1 lb Cl/10,000 lb plant
  material).
• Yield response associated with application rates
  20 to 50 times higher than that required to
  supply plant concentration requirements.
• Believed to function in internal water
  regulations and as a counter ion associated with
  excess cation uptake.
• Deficiencies have been reported in small grains
  (wheat and barley) grown in the central Great
  Plains (far from Cl containing ocean sprays and
  hurricanes) in soils that do not require annual K
  fertilization.
• The most common K fertilizer is KCl. Some crops
  also show a positive response to Cl fertilizer
  because of disease suppression (not a nutritional
  response). Chloride deficiency symptoms appear
  as chlorotic, leaf-spot lesions on older leaves
  (chloride is mobile in plants).

Chloride Research-Kansas State University
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Chlorine Deficiency.

• Occasionally found in wheat grown in sandy, low
  organic matter soils.

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Chlorine Deficiencies.

• Symptoms are yellow blotches on mature leaves.

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Chlorine Deficiencies.

• Limited to areas where potassium (K) fertilizer
  is not used.
• K fertilizer is usually potassium chloride.
• Soil test Cl is lt 20 lb/acre in top 2 feet.