Chapter 2NUTRIENT GENERAL CHEMISTRY AND PLANT FUNCTION

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

plant’s 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.

Nutrient

Symbol

Form Absorbed

Primary Source*

Soil Mobility**

Macronutrients (primary) Hydrogen H H2O Rainfall / soil solution M Oxygen O H2O, O2 Rainfall / soil solution M Carbon C CO2 Atmosphere - Nitrogen N NO3

- and NH4

+ Soil solution M and

I Potassium K K+ Soil solution / soil exchange sites I Calcium Ca Ca2+ Soil solution / soil exchange sites I Magnesium Mg Mg2+ Soil solution / soil exchange sites I Phosphorus P H2PO4

- and

HPO42-

Soil solution Soil solution

I I

Sulfur S SO42- and

SO2 Soil solution Atmosphere (minor source)

M

Micronutrients Iron Fe Fe2+ and

Fe3+ Soil solution (chelates) Soil solution (chelates)

I I

Chlorine Cl Cl- Soil solution M Boron B H3BO3 Soil solution M Manganese Mn Mn2+ Soil solution / soil exchange sites I Zinc Zn Zn2+ Soil exchange sites / chelates I Copper Cu Cu2+ Soil exchange sites / chelates I Molybdenum Mo MoO4

2- Soil solution I

CHOPKNS CaFe MgB Mn ClCuZn Mo

•A 17th Nutrient has been “added”.

•Sodium Na

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.

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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• 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

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

Cations Anions H+ Cl- Na+ O2- K+

Mg2+ Ca2+ Al3+

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)

Ion/molecule Name Oxidation State

NH3 ammonia -3

NH4+ ammonium -3

N2 diatomic N 0

N2O nitrous oxide +1

NO nitric oxide +2

NO2- nitrite +3

NO3- nitrate +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

• 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.

N is losing electrons to O because O is more electronegativeN gains electrons from H because H wants to give up electrons

Oxygen: oxidation number = -2Hydrogen: oxidation number = +1Nitrogen: oxidation number = 0

N Oxidation StateH 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

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.

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.

NH4+ (ammonium) SO4

2- (sulfate) CO32- (carbonate)

NO3- (nitrate) PO4

3- (phosphate) HCO3- (bicarbonate)

NO2- (nitrite) HPO4

2- (phosphate) MoO42- (molybdate)

NH30 (ammonia) H2PO4

- (phosphate) H3BO3o (boric acid)

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

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

• 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

“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

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

2 Fe3+ + 3 O2- + 3 H2O = Fe2O3 . 3H2O (rust)

2 Fe(OH)3

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

Multiple charged ions• Divalent cations Mg 2+ , Ca2+ , Mn2+ , Fe2+ , Cu2+ , Zn2+ • Divalent anions SO4

2-, CO32- (carbonate), HPO4

2-, and MoO42-

• Trivalent cations Fe 3+ and Al 3+ • Trivalent anion PO4

3-

• 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-, CO3

2-, HPO42-, MoO4

2-, 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 (CaSO4*2H2O).• 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 ?

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 HPO4

2-). Similarly, Ca3(PO4)2 has a charge sum of 5 (Ca 2+ and PO4

3-) and is less soluble than CaHPO4.

Relative solubility of compounds formed from the reaction of anions (An-) and cations (Mn+) of different charges.

M3+ M2+ M+ A- A2- A3- 1. All compounds with a monovalent ion are soluble. M3+ M2+ M+ A- A2- A3- 2. Compounds with both ions divalent are sparingly soluble. M3+ M2+ M+ A- A2- A3- 3. Compounds with one divalent ion and one trivalent ion are moderately

insoluble. M3+ M2+ M+ A- A2- A3- 4. Compounds with both ions trivalent are insoluble.

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

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.

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 SO 42- and

cause it to be somewhat immobile. Although sulfate compounds, such as CaSO4 and MgSO4 are relatively insoluble, the equilibrium concentration of SO4

2- 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 Fe+3 . • 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

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 (1.18%N) Soybeans (5.2%N)• 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.

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.

What are the Primary Nutrients needed by all cropsWhat are the Primary Nutrients needed by all crops

Nutrient

Nitrogen (N)

Potassium (K)

Phosphorus (P)

Soil (lb/a)*

400 – 8,000

800 - 60,000

400 – 10,000

Crop (lb/a)**

80

40

12

*Range of total amount in soil. From Chemical Equilibria in Soils. W.L.Lindsay, 1979. Wiley & Sons.

**Calculated for 2 ton crop yield (67 bushel wheat).

Secondary Nutrients Neededby all CropsSecondary Nutrients Neededby all Crops

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

* Range of total in soil. From Chemical Equilibria in Soils. W.L.Lindsay, 1979. Wiley & Sons.

**Calculated for 2 ton crop yield (67 bushel wheat).

Micronutrients Needed by all CropsMicronutrients 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*Range of total in soils. From Chemical Equilibria in Soils. W.L.Lindsay, 1979. Wiley & Sons.

Crop (lb/a)**

1

0.8

0.08

0.6

0.08

4

0.0008

**Calculated for 2 ton crop yield (67 bushel wheat).

Nutrient take up is Crop spec.

Review: Nutrients Needed by all CropsReview: Nutrients Needed by all Crops

PrimaryPrimary

Nitrogen (N)Nitrogen (N)

Potassium (K)Potassium (K)

Phosphorus (P)Phosphorus (P)

SecondarySecondary

Calcium (Ca)Calcium (Ca)

Magnesium (Mg)Magnesium (Mg)

Sulfur (S)Sulfur (S)

MicroMicro

Iron (Fe)Iron (Fe)

Zinc (Zn)Zinc (Zn)

Manganese (Mn)Manganese (Mn)

Copper (Cu)Copper (Cu)

Chlorine (Cl)Chlorine (Cl)

Boron (B)Boron (B)

Molybdenum Molybdenum (Mo)(Mo)

Nutrients not commonly found deficient in Oklahoma crops.• Calcium.

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

Nutrients seldom found deficient in Oklahoma crops.• Magnesium.• Sulfur.• Iron.• Zinc.• Boron.• Chlorine.

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).

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.htm

NitrogenIf 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.

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.

Nitrogen Deficiency in Corn.

chlorosis (yellowing) at the tip of the oldest chlorosis (yellowing) at the tip of the oldest leaf.leaf.

Nitrogen Deficiency in Corn.

Chlorosis continues to the Chlorosis continues to the next oldest leafnext oldest leaf

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

ATP• Biochemical reaction illustrating the release of energy and

primary orthophosphate when ATP is converted to ADP (R denotes adenosine).

O O O O O O R-O-P-O-P-O-P-OH energy + R-O-P-O-P-OH + O-P-OH OH OH OH OH OH OH ATP ADP Primary ortho phosphate (H2PO4

-)

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.

Phosphorus Deficiency.

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

CORN

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.

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

a. 1/10 the amount of Nb. 1/5 the amount of Nc. 1/2 the amount of Nd. Doesn’t matter, Bray said so

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.

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.

Potassium Deficiency.• Common in crops grown in weathered soils developed under high

rainfall.

                                                                

                                                      

K Usually adequate

K Usually deficient

Potassium Deficiency.• Chlorosis at the tip of the oldest leaf progressing toward

the base along the leaf margins (corn, alfalfa).

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.

N N Mg N N R

R

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.

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?)

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).

Magnesium Deficiency in Alfalfa.

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.

SulfurSulfur 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

Sulfur Deficiency in Corn.Overall light green color, worse on new leaves during rapid growth.

Overall light green color, worse on new leaves during rapid growth.

Sulfur Deficiency in Wheat.

Overall light green color, worse on new leaves during rapid growth.

Zinc Deficiency in Corn (Kansas).

Note short internodes (stunted plants).

Note “bronze” coloring of leaf.

Zinc Deficiency in Cotton (Mississippi)

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.

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.

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.

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

Iron Deficiency in Corn.

Note yellowing (chlorosis) between veins.

Iron Deficiency in Peanuts

Note yellowing (chlorosis) between veins of newest leaves.

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.

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.

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 (> 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)

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

Boron Deficiencies.

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

Chlorine• Since its discovery as an essential plant nutrient in the mid 1950’s, 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

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

soils.

Chlorine Deficiencies.• Symptoms are yellow “blotches’ on mature leaves.

Chlorine Deficiencies.• Limited to areas where potassium (K) fertilizer is not used.

• K fertilizer is usually potassium chloride.• Soil test Cl is < 20 lb/acre in top 2 feet.