Transcript Chapter 1 Introduction - SOIL 4234 Soil Nutrient Management

Chapter 2
NUTRIENT 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.
Form
Nutrient
Symbol Absorbed Primary Source*
Macronutrients (primary)
H
Hydrogen
H2 O
Rainfall / soil solution
O
Oxygen
H2 O, O2
Rainfall / soil solution
C
Atmosphere
Carbon
CO2
N
Nitrogen
NO3 - and Soil solution
NH4 +
K
Potassium
K+
Soil solution / soil exchange sites
2+
Ca
Calcium
Ca
Soil solution / soil exchange sites
2+
Magnesium
Mg
Mg
Soil solution / soil exchange sites
P
Phosphorus
H2 PO4 and Soil solution
HPO4 2Soil solution
2S
Sulfur
SO4 and
Soil solution
SO2
Atmosphere (minor source)
Micronutrients
Fe
Iron
Fe2+
and Soil solution (chelates)
3+
Fe
Soil solution (chelates)
Cl
Chlorine
ClSoil solution
B
Boron
H3 BO3
Soil solution
Mn
Manganese
Mn2+
Soil solution / soil exchange sites
2+
Zn
Zinc
Zn
Soil exchange sites / chelates
2+
Copper
Cu
Cu
Soil exchange sites / chelates
2Molybdenum Mo
MoO4
Soil solution
Soil
Mobility**
M
M
M and
I
I
I
I
I
I
M
I
I
M
M
I
I
I
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.
www.webelements.com
• 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
H+
Na+
K+
Mg2+
Ca2+
Al3+
Anions
ClO2WEB 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
Reduction, Net Gain of Electrons
Oxidation, Net Loss of Electrons
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
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.
Oxygen:
Hydrogen:
Nitrogen:
oxidation number = -2
oxidation number = +1
oxidation number = 0
H or O
NH3 Charge = 0 3(+1) = 3
NO3 Charge = -1 3(-2) = -6
NH4 Charge =+1 4(+1) = 4
3-(0))= +3
-6- (-1)) = -5
4 – (+1)) = 3
N Oxidation State
-3 N gains 3
+5 N loses 5
-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
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.
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.
NH4 + (ammonium)
NO3 - (nitrate)
NO2 - (nitrite)
NH3 0 (ammonia)
SO4 2- (sulfate)
PO4 3- (phosphate)
HPO4 2- (phosphate)
H2 PO4 - (phosphate)
CO3 2- (carbonate)
HCO3 - (bicarbonate)
MoO4 2- (molybdate)
H3 BO3 o (boric acid)
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 chargeinfluenced 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 =  Fe2 O3 . 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 Base
Strong Electrolyte
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 SO42-, CO32- (carbonate), HPO42-, and MoO42Trivalent cations Fe 3+ and Al 3+
Trivalent anion PO43When 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 (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 HPO42-).
Similarly, Ca3(PO4)2 has a charge sum of 5 (Ca 2+ and PO43-) and is less soluble
than CaHPO4.
Relative solubility of compounds formed
from the reaction of anions (An-) and
cations (Mn+) of different charges.
M 3+
M 2+
M+
A-
A 2-
A 3-
A 2-
A 3-
1. All compounds w ith a monovalent ion are soluble.
M 3+
M 2+
M+
A-
2. Compounds w ith both ions divalent are sparingly soluble.
M 3+
M 2+
M+
A-
A 2-
A 3-
3. Compounds w ith one divalent ion and one trivalent ion are moderately
insoluble.
M 3+
M 2+
M+
A-
4. Compounds with both ions trivalent are insoluble.
A 2-
A 3-
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 SO42and 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 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 crops
*Range of total amount in soil. From Chemical Equilibria
in Soils. W.L.Lindsay, 1979. Wiley & Sons.
Nutrient
Soil (lb/a)*
Crop
(lb/a)**
Nitrogen (N)
400 – 8,000
80
Potassium (K)
800 - 60,000
40
Phosphorus (P)
400 – 10,000
12
**Calculated for 2 ton crop yield (67 bushel wheat).
Secondary Nutrients Needed
by all Crops
* Range of total in soil. From Chemical Equilibria in Soils.
W.L.Lindsay, 1979. Wiley & Sons.
Nutrient
Soil (lb/a)*
Crop (lb/a)**
Calcium
14,000 – 1,000,000
16
Magnesium
1,200 - 12,000
8
Sulfur
60 – 20,000
6
**Calculated for 2 ton crop yield (67 bushel wheat).
Micronutrients Needed by all Crops
Nutrient
Soil (lb/a)*
Crop (lb/a)**
Iron
14,000 – 1,100,000
1
Manganese
40 – 6,000
0.8
Copper
4 - 200
0.08
Zinc
20 - 600
0.6
Boron
4 - 200
0.08
Chlorine
40 – 1,800
4
Molybdenum
0.4 - 10
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).
Nutrient take up is Crop spec.
Review: Nutrients Needed by
all Crops
Primary
Secondary
Micro
Nitrogen (N)
Calcium (Ca)
Iron (Fe)
Potassium (K)
Magnesium (Mg)
Zinc (Zn)
Phosphorus (P)
Sulfur (S)
Manganese (Mn)
Copper (Cu)
Chlorine (Cl)
Boron (B)
Molybdenum
(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
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.
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
leaf.
Nitrogen Deficiency in Corn.
Chlorosis continues to the
next 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



R-O-P-O-P-O-P-OH  energy +



OH OH OH
ATP
O


R-O-P-O-P-OH +


OH OH
ADP
O
O

O-P-OH

OH
Primary ortho phosphate (H2 PO4 -)
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.
CORN
purple coloring and sometimes
yellow on lower (oldest) leaves.
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.
b.
c.
d.
1/10 the amount of N
1/5 the amount of N
1/2 the amount of N
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.
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
Sulfur Deficiency in Corn.
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 inseason.
• 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.