This document discusses essential plant nutrients and how they are classified. It outlines that 17 elements are considered essential for plant growth according to specific criteria. These elements can be classified based on their concentration in plants as either macronutrients, which are needed in larger quantities, or micronutrients, which are needed in smaller amounts. They can also be classified into four groups based on their biochemical behavior and physiological functions in plants. The four groups include elements that are major constituents of organic materials, involved in biochemical reactions, present in free ionic states or adsorbed to organic anions, or predominantly present as chelates.

1. By Dilip Kumar Chandra

2. Introduction
• The element is involved directly in the nutrition of the plant quite apart
from its possible effects in correcting some unfavourable
microbiological or chemical condition of the soil or other culture
medium.
Essential plant nutrients
A total of only 17 elements are essential for the growth and full
development of higher green plants according to the criteria laid down
by Arnon and Stout (1939). These criteria are:
• A deficiency of an essential nutrient makes it impossible for the plant
to complete the vegetative or reproductive stage of its life cycle.
• Such deficiency is specific to the element in question and can be
prevented or corrected only by supplying this element.

3. However, this list may not be considered as final
and it is probable that more elements may prove to
be essential in future. The chronology of
discoveries of essential nutrient elements is given
in Table (see next slide).
Introduction
The essentiality of most micronutrients for
higher plants was established between
1922 and 1954.
The essentiality of nickel (Ni) was established in 1987
by Brown et al., although there is no unanimity among
the scientists as to whether Ni is essential or beneficial.
Essential plant nutrients

4. Element Discoverer of
Essentiality
Year
Carbon (C)
Hydrogen (H)
Oxygen (O)
Nitrogen (N)
Phosphorus (P)
Potassium (K)
Sulphur (S)
Calcium (Ca)
Magnesium (Mg)
DeSaussure
DeSaussure
DeSaussure
DeSaussure
Ville
von Sachs, Knop
von Sachs, Knop
von Sachs, Knop
von Sachs, Knop
1804
1804
1804
1804
1860
1860
1865
1860
1860
(Glass, 1989; Marschner, 1997)
Chronology of discoveries of essential nutrient elements for higher plants
Essential plant nutrients

5. Element Discoverer of
Essentiality
Year
Iron (Fe)
Manganese (Mn)
Copper (Cu)
Zinc (Zn)
Molybdenum (Mo)
Boron (B)
Chlorine (Cl)
Nickel (Ni)
von Sachs, Knop
McHargue
Lipman and
MacKinney
Sommer and Lipman
Arnon and Stout
Warington
Broyer et al.
1860
1922
1931
1926
1938
1923
1954
1987
(Glass, 1989; Marschner, 1997)
Chronology of discoveries of essential nutrient elements for higher plants
Essential plant nutrients

6. Classification of essential plant nutrients
Essential plant nutrients

7. Oxygen, carbon and hydrogen make
up 95 percent of plant biomass, and
the remaining 5 percent is made up by
all other elements.
Frame-work nutrient elements
Carbon (C) and oxygen (O) are obtained
from the gas CO2, and hydrogen (H) is
obtained from water (H2O).
These three elements are required in
large quantities for the production of
plant constituents such as cellulose or
starch.
Hence, many times referred as frame-
work elements.
Essential plant nutrients

8. Mineral nutrient elements
The difference in plant concentration between
macronutrients and micronutrients is enormous. The
relative contents of N and molybdenum (Mo) in
plants is in the ratio of 10,000:1. Plants need about
40 times more magnesium (Mg) than Fe.
14 elements are called mineral nutrients because they
are taken up in mineral (inorganic) forms. They are
traditionally divided into two groups, macronutrients
and micronutrients, according to the relative amounts
required.
The 14 mineral elements are taken up by plants in
specific chemical forms regardless of their source.
Essential plant nutrients

9. Ca, Mg, and S are referred to as secondary
nutrients and are also found in fertilizers and soil
amendments.
Macronutrients
Macronutrients are nitrogen (N), phosphorus (P), potassium
(K), calcium (Ca), magnesium (Mg), and sulphur (S).
The one or two letter symbol in parentheses is the universal
chemical symbol for that nutrient.
N, P, and K are often referred to as primary nutrients and
are the most common elements found in commercial
fertilizers.
Essential plant nutrients

10. Micronutrients
Micronutrients are required in relatively minute
quantities and rarely limit plant growth in the
environment.
Note: Cobalt (Co), sodium (Na), vanadium (V) and silicon (Si) are
sometimes called as beneficial plant nutrients. They are not
required by all plants but appear to benefit certain plants. Cobalt is
required for nitrogen fixation in legumes. Silicon is found in plant cell
walls and appears to produce tougher cells. This increases the
resistance of these plants to piercing and sucking insects and
decreases the spread of fungal diseases.
Micronutrients include iron (Fe), manganese (Mn),
zinc (Zn), boron (B), copper (Cu), chloride (Cl),
molybdenum (Mo), and nickel (Ni).
Essential plant nutrients

11. Element Symbol mg/kg percent
Relative
number
of atoms
Nitrogen N 15,000 1.5 1,000,000
Potassium K 10,000 1.0 250,000
Calcium Ca 5,000 0.5 125,000
Magnesium Mg 2,000 0.2 80,000
Phosphorus P 2,000 0.2 60,000
Sulphur S 1,000 0.1 30,000
(Epstein, 1965; Epstein and Bloom, 2005)
Typical concentrations of nutrient elements sufficient for plant growth
Essential plant nutrients

12. Relative concentration of essential elements in plants
Aluminium and manganese toxicity are the most
frequent ones, in direct relation with acid soils. The
concentration of different essential elements
sufficient for plant growth are given in Table (Next
slide).
Some microelements can be toxic for plants at
levels only somewhat higher than normal. In
the majority of the cases this happens when
the pH is low to very low.
Essential plant nutrients

13. Element Symbol mg/kg percent
Relative
number
of atoms
Chlorine Cl 100 -- 3,000
Iron Fe 100 -- 2,000
Boron B 20 -- 2,000
Manganese Mn 50 -- 1,000
Zinc Zn 20 -- 300
Copper Cu 6 -- 100
Molybdenum Mo 0.1 -- 1
Nickel Ni 0.1 -- 1
Typical concentrations of nutrient elements sufficient for plant growth
Essential plant nutrients
(Epstein, 1965; Epstein and Bloom, 2005)

14. Classification of plant nutrients based on biochemical
behaviour and physiological functions
Group IV includes Fe, Cu, Zn and Mo. These
elements are predominantly presented as
chelates in the plant.
Mengel and Kirkby (1987) have divided essential plant nutrients into
four groups (pl. see Table on the next slide).
Group I includes C, H, O, N and S, which are major constituents
of the organic plant materials (carbohydrates, proteins, fats, etc.).
Group II includes P and B, which are involved in
biochemical reactions such as esterification.
Group III includes K, Ca, Mg, Mn and Cl. These elements are
present in the free ionic state or are adsorbed to indiffusible
organic anions (e.g. absorption of Ca2+
by the carboxylic
group of pectins).
Essential plant nutrients

15. Group Nutrients Form in which
taken up by plants
Biochemical/physiological functions
I C CO2, HCO3
-
Major constituents of organic material, essential
elements of atomic groups which are involved in
enzymatic process, etc.
H H2O
O O2
N NH4
+
, NO3
-
, N2 (in
fixation)
S SO4
-2
, SO2
(gaseous absorption
in leaves
II P H2PO4
-1
, HPO4
-2
Esterification with native plant alcohol. Phosphate
esters are involved in energy transfer.B B(OH)3
Classification of essential plant nutrients on the basis
of biochemical and physiological functions in plants
Essential plant nutrients

16. Group Nutrients Form in which
taken up by plants
Biochemical/physiological functions
III K K+
Nonspecific functions, involved in establishing
osmotic potential. Ca is a component of plant
structural parts.
Mg Mg+2
Ca Ca+2
Mn Mn+2
Cl Cl-1
IV Fe Fe+2
Present predominantly in a chelated form in
prosthetic group, enable electron transport by
valency change
Cu Cu+2
Classification of essential plant nutrients on the basis
of biochemical and physiological functions in plants
Essential plant nutrients

17. Let Us Sum Up
Plant nutrients can also be classified
based on their biochemical behaviour
and physiological functions in plants.
Seventeen elements are considered
as essential plant nutrients for higher
plants.
They are generally classified based
upon their relative concentration in
plants.
They are also classified based upon
their biochemical behaviour and
physiological functions.
Mineral nutrients (14) are taken up by
plants in ionic forms.
Essential plant nutrients