CHAPTER 2
CLASSIFICATION OF PLANT
NUTRIENTS
THE ROLE OF ESSENTIAL ELEMENTS
IN CROP NUTRITION
NUTRIENT DEFICIENCY AND
TOXICITY SYMPTOMS
Prof. K. SÁRDI
NUTRIENT MANAGEMENT
Plant nutrients
Nutrition = Supply and absorption of chemical compounds and/or elements
elements (ions) needed for
plant growth and metabolism
Nutrition
→
metabolism ( = biochemical reactions i. the cell (plant)
During life processes (vegetation period) → Biomass production
Crops = plant species grown in agriculture for human use
Nutrients = elements or chemical compounds (ions)
ions) required by an organism (crop)
crop)
DEFINITION OF ESSENTIAL NUTRIENTS
Elements (nutrients) required by the plants for normal growth and developmenand not
replacable in their function by another are referred essential (Mengel, 1982).
Essential nutrients ← 3 criteria must be met
1.
2.
3.
A deficiency of the element makes it impossible for the plant to complete its life cycle
The deficiency is specific for the given element and not replaceable
replaceable by another
The element is a constituent of an essential metabolite or req
required for the action of an
anzyme system.
(Arnon and Stout 1939, Mengel 1982)
1982)
Classification of plant nutrients
Elements representing the mineral composition of plants =
Essential and Other Mineral Elements
Based on concentrations: macronutrients 0.02 – 6.0 %
micronutrients 0.01 – 500 mg/kg
Based on physiological functions:
1.
Constitutents of organic or inorganic compounds
N, S, P, Ca, B, Fe and Mg
2.
Activators of enzymes
3.
Components of redox systems and electron transport: P, S, Fe, Mn Cu, Mo
4.
Osmotic regulators and maintain ionic balance: K, Na and Cl
5.
Stimulating (beneficial) elements
6.
Toxic heavy metals and other elements:
K, Mg, Ca, Fe, Zn, Mn, Cu, Mo, Na and Cl
Co, Cr, Ni, V, Sn, Li, F, Se, Si etc.
Cd, Cr, Hg, Ni, Pb, As, Se, V
IMPORTANT
With the development of analytical methodologies and advances
in plant physiology, lowest measurable amounts of elements were
decreasing. Lowest measurable amount: pg (picogram= 10-12 g)
RECENT CONSIDERATION OF ESSENTIAL AND OTHER
(NONESSENTIAL AND TOXIC) NUTRIENT ELEMENTS IN
CROPS
a.) Excessive concentration of a mineral element – both macro- and
microelements - can cause nutrient imbalances, reduction in growth
and yield losses. The element has been considered as „toxic”.
b.) Plants may contain small amounts of elements with no evidence of
essentiality: Fluorine (F), Arsenic (As), Chromium
(Cr), Lithium (Li), Lead (Pb).
New terms were introduced by Epstein (1999), Epstein & Bloom (2005).
•
•
•
Instead of the term „nonessential”, it is suggested to use the term
„apparently nonessential” or not known to be essential.
The element is classified as „quasi-essential” when essentiality and
plant responses are different among plant species.
It is suggested to use the term „toxic concentration” rather then
„toxic element”.
c.) Other terms used by several authors: „beneficial” elements
(Pilon-Smits et al., 2009).
Aluminum (Al), cobalt (Co), sodium (Na), selenium (Se), and silicon
(Si) are considered „beneficial” elements for plants: they are not
required by all plants but can promote plant growth and may be
essential for several plant species.
d.) Silicon is considered a „quasi essential” element for plants
because its deficiency can cause various abnormalities with respect
to plant growth and development. This term was introduced by
Epstein (1999), Epstein & Bloom (2005).
Essential nutrients (Mengel 1982, Frageria et al. 1995)
Element
Chemical
symbol
Principal
form(s) taken
up by roots
Described as
essential
Year
Author
Macronutrients
Carbon
C
CO2
1882
Sachs, J.
Hydrogen
H
H2O
1882
Sachs, J.
Oxygen
O
H2O, O2
1804
De Saussure, T.
Nitrogen
N
NH4+, NO3-
1872
Rutherford, G.K.
Phosphorus
P
H2PO4-, HPO42-
1860
Ville
Potassium
K
K+
1860
Sachs, J., Knop
Calcium
Ca
Ca2+
1856
Salm-Horstmar,
F.
Magnesium
Mg
Mg2+
1906
Willstatter
Sulfur
S
SO42-
1865
Sachs, J. , Knop
Micronutrients
Iron
Fe
Fe2+, Fe3+
1860
Sachs, J., Knop
Zinc
Zn
Zn2+, Zn(OH)2
1926
Sommer and Lipman
Manganese
Mn
Mn2+
1922
McHargue
Copper
Cu
Cu2+
1931
Lipman and
MacKinney
Boron
B
B(OH)3
1923
Warington
Molybdenum
Mo
MoO42-
1938
Arnon and Stout
Silicon* *
Si
Si(OH)40
1980’s
Sodium*
Na
Na+
1980’s
Chlorine*
Cl
Cl-
1954
Broyer, Stout
Nickel
Ni
Ni2+
1983
Brown, Welsh &Cary
Cobalt
Co
Co2+
1980’s
Vanadium
V
V+
1987
* Macronutrients for several crops
* * ”Quasi-Essential Element”
Expressing plant nutrient content
Recently, nutrient content is expressed as element
content in dry matter (DM)
percentages in DM for macroelements:
N %, P %, K %, Ca %, Mg %, S %
mg per kg (mg kg-1 ) in DM for microelements (also
known as ppm= pars pro million, 1mg per 106)
Previously, element contents were commonly expressed
as oxides (e.g. P2O5 , K2O etc.)
Conversion factors:
P2O5 % x 0.436 = P % or P % x 2.29 = P2O5
K2O % x 0.83 = K%
or K % x 1.2 = K2O
AVERAGE CONCENTRATION RANGES OF ESSENTIAL NUTRIENT
ELEMENTS IN CROPS
Macroelements
Concentration range
percentages in DM
O
45
C
45
H
6
N
0.1 – 6.0
P
0.01 – 0.7
K
0.2 – 6.0
Ca
Microlements
Concentration
range mg per kg
in DM
Fe
50 – 250
Mn
20 – 500
Zn
25 – 150
Cu
2 – 20
0.2 – 1.0
B
6 – 60
Mg
0.1 – 0.4
Mo
± 1
S
0.1 – 0.4
Co
0.02 – 0.5
Si
0.2 - 2.0
Ni
0.05
Cl
0.2 – 2.0
V
± 1
Na
0.01 – 10
MECHANISMS OF ION TRANSPORT TO PLANT ROOTS
3 Mechanisms are known in which nutrients reach the root surface:
- Root interception
- Mass flow
- Diffusion movement
-
Rates of Root interception, Mass Flow and Diffusion in Ion Transport to Corn
Roots (Havlin et al. 2005)
Nutrient
Root
interception
Mass Flow
Diffusion
movement
Pecentages in Supply
Nitrogen N
1
99
0
Phosphorus P
2
4
94
Potassium K
2
20
78
Calcium Ca
12
88
0
Magnesium Mg
27
73
0
Sulphur S
4
94
2
Part 2
THE ROLE OF ESSENTIAL ELEMENTS
IN CROP NUTRITION
Functions of essential nutrients in plants
Nutrient
Carbon
Oxigen
Function
Basic molecular component of carbonydrates,
carbonydrates, proteins, lipids and nucleic acids.
Occurs in all organic compounds of living organisms.
Hydrogen
Plays a central role in plant metabolism. Important in ionic balance,
balance, as main
reducing agent, and plays a key role in energy relations of cells.
cells.
Nitrogen
Plays a significant role in the synthesis of important organic compounds,
amino acids,
acids, proteins,
proteins, nucleic acids (RNA, DNA), enzymes etc.
Phosphorus
Important component of proteins and enzymes,
enzymes, nucleic acids (DNA and
RNA) and phytin.
phytin. P is involved in various energy transfer reactions of
adenosine triphosphate and diphosphate (ATP and ADP).
Potassium
Helps in osmotic and ionic regulation. Potassium is a cofactor or activator for
many enzymes of carbohydrate and protein metabolism.
Calcium
Involved in cell division and plays a major role in the maintenance of membrane
membrane
integrity.
Magnesium
Sulfur
Component of chlorophyll and cofactor for many enzymatic reactions.
reactions.
Somewhat like phosphorus,
phosphorus, it is involved in plant cell energetics.
energetics. Plays an
important role in plant lipid synthesis.
synthesis.
Iron
An essential component of many heme nonheme Fe enzymes and carrires,
carrires,
including the cytochromes (respiratory election carriers) and these ferredoxins.
ferredoxins.
The latter are involved in key metabolic functions such as N fixation,
fixation,
photosynthesis and electron transfer.
Zinc
Essential component of several enzyme systems (dehydrogenases
(dehydrogenases,, proteinases
and peptidases including carbonic anhydrase,
anhydrase, alcohol dehydrogenase and
others).
Manganese
Involved in the O2O2-evolving system of photosynthesis and is a component of
the enzymes arginase and photosphotransferase.
photosphotransferase.
Copper
Constituent of a number of important enzymes, including cyctochrome oxidase.
oxidase.
Ascorbic acid oxidase and lactase.
Boron
The specific biochemical function of boron is unknown, but it may
may be involved
in carbonydrate metabolism and sythesis of cell wall components.
Molybdenum
Required for the normal assimilation of N in plants. An essential
essential component on
nitrate reductase as well as nitrogen (N2 fixation enzyme).
Vanadium
Stimulates biological N fixation of bacteria (Azotobacter
(Azotobacter,, Rhizobium sp.)
similarly to Molybdenum.
V has an important role in the food chain (essential for animals and humans)
Chlorine
Essential for photosynthesis and as an activator of enzymes involved
involved in
splitting water. It also functions in osmoregulation of plants growing on saline
soils.
NITROGEN
N
Elemental N (N2) constitutes 99.8 % of global N and
78 % of the atmosphere is N2.
Available forms and usual concentrations in plants
Available forms for roots: ammonium (NH4+) and nitrate (NO3-)
Concentration range in plants: 0.8-6.0 % in DM weight
Nitrogen is found in both inorganic and organic forms in the plant.
Forms of N in the environment:
a.) gaseous: nitrous oxide (N2O), nitric oxides (NOx), ammonia
(NH3)
b.) inorganic compounds and ions: ammonium (NH4+) and nitrate
(NO3-)
c.) organic forms: urea CO(NH2)2, amino acids, proteins, enzymes,
etc.
Effects of ammonium-N and nitrate-N supply
1.) NO3- reduction is an energy-requiring process (reduction of each
NO3- ion requires 2 molecules of NO3- reductase for protein
synthesis.
2.) When plants take up high levels of NO3 –N, an increase in cation
(K+, Ca++, Mg++) absorption will occur.
3.) High levels of NH4+ -N may be toxic for cells and retard growth.
Due to the ion antagonism, restricts K uptake.
4.) Cerals, corn, rice, pineapple use both forms of N while potato,
tomato and other solanaceae crops prefer a high nitrate/ammonium
ratio for optimum growh.
PHOSPHORUS
P
Available forms and usual concentrations in plants
P exist in most soils in organic forms (about 50-70 % of total P) and
inorganic forms (about 30-50 % of total P).
The main available anion forms of P for roots are orthophosphates:
Dihydrogen phosphate
H2PO4-
Monohydrogen phosphate
HPO42-
Their ratio is depending on soil pH: at pH 6.0 and about 90 % of
phosphates exist as H2PO4- whereas at pH 8.0 the ratio is just the
reverse.
Concentration range in plants: 0.15 – 0.7 % P in DM weight of crops,
depending
on species and plant parts.
Main functions of PHOSPHORUS in
plants
a.) P is a constituent of nucleic acids (RNA and DNA),
phospholipids, phosphoproteins, nucleotids and
membrane biochemistry.
b.) Almost every metabolic reaction requires and involves
phosphates.
c.) As energy obtained from photosynthesis and
carbohydrate metabolism is stored in P compounds,
growth and reproduction functions are strongly
depending on the level of P supply.
Potassium K
Available forms and usual concentrations in plants
Available forms of potassium for plant uptake: K+ in soil solution
and exchangeable K+ adsorbed on soil colloids.
An equilibrium exists between K forms: exchangeable K,
nonexchangeable K (fixed in the clay minerals).
Adequate K concentration range of plants: 1.0 - 6.0 %, highest
concentrations: in young leaves and plant stems.
Excess absorption of plants is referred to as „luxury
consumption”. Nutrient ratios (balanced nutrition!) of either K/Ca
or K/Mg are important in crops.
Main functions of POTASSIUM in plants
Unlike N and P, K is not a component of biochemical compounds:
exists as K+ ion.
K is required in a wide range of physiological functions:
- for the normal water status of plants: regulates the osmotic
pressure in cells and across membranes (K/Ca interaction),
- in maintaining the turgor pressure of cells,
- for the opening and closing of stomata
Plays a significant role in the accumulation and translocation of
carbohydrates (sugars and starch)
Plays a key role in enzyme activation: involved in the function
and activity of more than 60 enzymes
K is required for the translocation of assimilates, ATP and protein
synthesis
K stimulates resistance to pests and diseases (cell walls are
thicker in good K status), color, taste, vitamins and other quality
parameters in fruit and vegetable crops
Calcium Ca
Functions in plants
Plays an important role in
•maintaining membrane permeability
•enhances pollen germination and growth
•activates a member of enzymes for cell mitosis and elongation
•Ca is required in avoiding the toxicity effects of heavy metals in plants.
Available forms and usual concentrations in plants
Calcium exists as Ca++ cation in the soil. In soils with high pH values,
Ca++ has the highest concentrations among cations, in both soluble and
exchangeable forms.
Ca is taken up by plants as Ca++ (availability is affected by soil pH and
moisture)
Calcium content in the DM of plants ranges between 0.20 to 5.00 %.
Critical values of Ca vary considerably among crop species.
Magnesium
Mg
Functions in plants
Magnesium is a component of the cholorphyll molecule, serves as a cofactor
in most enzymes that activate phosphorylation processes – as a bridge
between pyrophosphate structures of ATP or ADP and the enzyme molecule.
Available forms and usual concentrations in plants
Magnesium can be found in the soil solution as Mg++ cation and as
exchangeable Mg++ on soil colloids.
Magnesium content in plant DM ranges between 0.15% and 1.00%. The Mg
content in leaves increases with age.
The relationship between Mg and K is well kown, as is the relationship
between mg and Ca.
I.Microelements
B, Cu, Fe, Mn, Mo, Zn
Functions in plants
Micronutrients Cu, Fe and Mn are involved in various processes related
to photosynthesis. Cu, Fe and Zn are associated with various enzyme
sysmtes, Mo is specific for nitrate reductase only.
Boron is associated with the carbonydrate metabolism of plants and the
pollen germination.
Available forms and usual concentrations in plants
Elements
Available forms
Concentration mg/kg
Boron
B
H3Bo3
6-60
Copper
Cu
Cu2+
2-20
Iron
Fe
Fe2+, Fe3+
5050-250
Manganese
Mn
Mn2+
2020-500
Molybdenum
Mo
MoO42-
~1
Zinc
Zn
Zn2+
2525-150
Critical values of microelement concentrations vary considerably among
crop species.
Part 3
NUTRIENT DEFICIENCY AND TOXICITY
SYMPTOMS
NUTRIENT DEFICIENCY AND TOXICITY
SYMPTOMS OF CROPS
General description of deficiency and
toxicity
Concentration ranges used in plant
analysis and interpretation
Visual symptoms of deficiencies
Visual symptoms of toxicities
Concentration Ranges:
Deficient, Critical, Sufficient or Normal, Excessive or Toxic are
known and used for laboratory results interpretation.
Example: K and P % concentration ranges for corn
Deficient
Critical
Sufficient
K
< 1.25
1.26-1.5
2.1-4.0
P
<0.15
0.32
0.4-0.8
High
Toxic
2.45
Relationship between plant nutrient concentration and plant
growth/yield
Souce: (Havlin et al.
al. 2005)
Steenberg effect: under extreme deficiency, rapid yield increase can
cause some decreases in nutrient concentration.l
General Deficiency symptoms of N
In nitrogen deficiency, the most typical symtoms are: leaf chlorosis,
leaves turn brown and die
Excess (toxiticy) symptoms
Excess nitrogen : vigorous vegetative growth, dark green colour,
prolonged vegetative growth, delayed crop maturitiy.
Important: nutrient ratios in plants!
N/P
N/K
N/S
Imbalances of these ratios may depress yield levels and quality
SYMPTOMS OF
NITROGEN DEFICIENCIES
Wheat
Sunflower
Potatoes
Grapevine
Peach
Deficiency symptoms of P
Slow-growing, weak plants. A typical dark green colour on older
leaves showing a purple pigmentation (anthocyanes).
Since P is mobile in the plant, deficiency symptoms initially occur
in the older tissue (indicating the ability for reutilization)
Excess (toxiticy) symptoms
Excess of P appears mainly in the form of micronutrient deficieny
mostly for Fe, Zn and Mn.
Excess P may also cause typical Ca deficieny symptoms.
SYMPTOMS OF P DEFICIENCIES
MAIZE
Wheat
K
Sunflower
SYMPTOMS OF P DEFICIENCIES
Sweet Melon
Sweet cherrry
P deficiency on pepper
Root beet
Deficiency symptoms of K
Crops deficient in K are sensitive to diseases. Fruit yield and quality
will be reduced. Leaves show symptoms of being burned.
Excess (toxiticy) symptoms
Plants show typical symptoms of Mg and possibly Ca deficiency due
to a cation imbalance in the plant.
SYMPTOMS OF POTASSIUM DEFICIENCIES
Trofolium
sp.
Plum
Oilseed
rape
Grapevine
Maize
Deficiency symptoms of Ca
• The growing tips of leaves and roots turn brown and die.
• Reduced structural stability of cell membranes.
• Reduced root hair function in nutrient and water uptake.
Excess (toxiticy) symptoms
Excessive Ca content will produce Mg or K deficiency in plants,
depending on the concentration of these elements.
Ca toxiticy symptoms have not been reported for crops under field
conditions.
SYMPTOMS OF Ca
DEFICIENCIES
Apple
Cabbage
Deficiency symptoms of Mg
Mg deficiency causes intervenial chlorosis
reduced chlorophyll
synthesis in leaves.
Mg deficiency begins on older leaves as mg is a mobile element in
plants.
Excess (toxiticy) symptoms
No specific toxiticy symptoms are known for Mg.
Imbalances among K, Ca, and mg may induce reduced growth when
mg content growth when Mg content is extremeley high.
SYMPTOMS OF Mg DEFICIENCIES
Oilseed
rape
Wheat
Grapevine
Plum
SZŐLŐ
SYMPTOMS OF SULFUR DEFICIENCIES
Oilsedd
rape
Maize
Deficiency symptoms of micronutrients
Symptoms of micronutrient deficiency are: reduced or abnormal
growth, bleaching and necrosis of leaves, intervenial chlorosis and
other symptoms typical for the given crop.
Excess (toxiticy) symptoms
Excess or toxic amounts of micronutrients may result a premature
yellowing and burning of the leaves, as well as leaf abcission. Root
growth may be reduced, restricting the uptake of water and several
nutrients from the soil.
Typical symptoms of both deficiencies and toxicities are described in
nutrition manuals and other books.
SYMPTOMS OF IRON DEFICIENCIES
Grapevine
Soybean
SYMPTOMS OF Zn DEFICIENCIES
Onion
Maize
SYMPTOMS OF
BORON DEFICIENCIES
Sugarbeet
Sunflower