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🧫 Forms of nutrients

Forms of nutrients.

This lesson introduces essential plant nutrients, their categories, concentration ranges, and absorbable ionic forms relevant to soil fertility management.

Learning objective

To know the functions of each nutrient in plant

Primary or major nutrients: are those nutrients required relatively in large quantities by the plants for its growth and development. Ex: N, P and K.

Secondary nutrients: are those nutrients which are required by plants in moderate amounts and given secondary importance in its supply and management.

Ex: Ca, Mg and S.

Micronutrients: The nutrients which are utilized by plants in relatively smaller quantities for their growth and development, but these are equally important & essential to plants as macronutrients.

Ex: Fe, Mn, Zn, Cu, B, Mo, Cl and Ni.

Plant Nutrients

Sixteen elements are considered essential for plants. They are grouped based on their

relative abundance in plants.

Many non-essential elements are also found in plants that account for over 60

elements. Al is absorbed when soil solution is rich in Al ions. When plant materials is

burned, the remaining plant ash contains all the essential and non-essential elements

except C, H, O, N, S. Macro nutrients are absorbed in 30-100 times in proportion to that of

micronutrients.

Essential Nutrients

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Non- mineral Nutrients	Macronutrients	Col3	Micronutrients	Col5
Non- mineral Nutrients	Primar y	Secondary	By all plants	Some

C	N	Ca	Fe	B	Na
H	P	Mg	Mn	Cl	Co
O	K	S	Zn	Mo	Va
			Cu		Ni
					Si

Chemical nature

Metals	K, Ca, Mg, Fe, Mn, Zn, Cu,
Non-metals	C, H, O, N, P, S, Cl

The plant content of mineral elements is affected by many factors and their

concentration in crops varies considerably.

Nutrient	Col2	Relative concentration (Times)	Concentration (%)
Primary	N, K	400-1000	1-1.5
	P	30	0.1-0.3
Secondar y	Ca, Mg	100-200	0.2-0.5
	S	30	0.1
Micro	Fe, Mn, B	1-2	0.002-0.01
	Others	<1	<0.002

2 Plant Nutrients

Concentration, Mobility, forms, functions

A mineral element is considered essential to plant growth and development if the element

is involved in plant metabolic functions and the plant cannot complete its life cycle without the

element. Terms commonly used to describe level of nutrients in plants are

Deficient

When the concentration of an essential element is low enough to limit yield severely and distinct

deficiency symptoms are visible then that element is said to be deficient. Extreme deficiencies

can result in plant death. With moderate or slight deficiencies, symptoms may not be visible, but

yields will still be reduced.

Critical range

The nutrient concentration in the plant below which a yield response to added nutrient occurs.

Critical level or ranges vary among plants and nutrients but occur somewhere in the transition

between nutrient deficiency and sufficiency.

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PLANT YIELD

NUTRIENT CONCENTRATION IN TISSUE

Sufficient

Concentration range in which added nutrients will not increase yield but can increase nutrient

concentration. The term luxury consumption is used to describe nutrient absorption by the plant

that does not influence yield.

Excessive or toxic

When the concentration of essential or other elements is high enough to reduce plant growth and

yield then it is said to be toxic. Excessive nutrient concentration can cause an imbalance in other

essential nutrients, which also can reduce yield

Concentration and plants yield

Yield is severely affected when a nutrient

is deficient. When deficiency is corrected, growth

increases more rapidly. Under severe deficiency,

rapid increase in growth with added nutrient can

cause a small decrease in nutrient concentration

due to dilution effect. This is called the

Steenberg effect

Luxury consumption

Nutrient sufficiency occurs over a wide

concentration range, wherein yield is unaffected.

Increase in nutrient concentration above the

critical range indicates that the plant is absorbing

nutrient above that needed for maximum yield.

Forms of nutrients for Plant absorption	Col2
N	NH4 +, NO3 -, organic N
P	H2PO4 - (Primary) and HPO4 2- (Secondary) Orthophosphates
K	K+
Ca	Ca++
Mg	Mg++
S	SO3 - (Sulphite) and SO4 -
Fe	Fe++ (Ferrous), Fe+++ (Ferric)
Mn	Mn++(Manganous) and Mn+++ (Manganic) 1 (2/
Zn	Zn++
Cu	Cu+ (Cuprous) and Cu++ (Cupric)
B	BO3 - and other forms
Mo	MoO4 -- (Molybdate)
Cl	Cl-

This luxury consumption is common in most plants. Elements absorbed in excessive quantities

can reduce plant yield directly through toxicity or indirectly by reducing concentration of other

nutrient below critical ranges.

Functions of nutrients in plants:

Nutrient	Col2	Functions
Major nutrients	Major nutrients	Major nutrients
Nitrogen		Basic component of proteins and chlorophyll (the pigment that gives plants their green colour). Plays an essential role in plant growth. Also feeds microorganisms in the soil
Phosphorus		Plays an important role in root growth and promotes the establishment of young plants, flowering, fruiting and ripening, photosynthesis, respiration and overall plant growth.
Potassium		Moves through the plant. Promotes the movement of sugars, turgor and stem rigidity. Also increases the plant’s overall resistance to cold, diseases, insect pests, etc. Promotes the formation of flower buds, the hardening-off of woody plants and fruiting.
Secondary nutrients	Secondary nutrients	Secondary nutrients
Calcium		Plays a vital role in plant structure, because it is part of cell walls and holds them together. Promotes the development of the root system and the ripening of fruit and seeds. Found in the growing parts of plants (apex and buds).
Magnesium		An important part of chlorophyll. Helps fruit ripen and seeds germinate. Reinforces cell walls and promotes the absorption of phosphorous, nitrogen and sulphur by plants
Sulphur		A component of several proteins, enzymes and vitamins. Contributes to chlorophyll production. Helps plants absorb potassium, calcium and magnesium.
Micronutrients	Micronutrients	Micronutrients

Iron	Col2	Essential to chlorophyll production. Also contributes to the formation of some enzymes and amino acids.
Boron		Essential to overall plant health and tissue growth. Promotes the formation of fruit and the absorption of water.
Manganese		Promotes seed germination and speeds plant maturity. Plays an important role in photosynthesis by contributing to chlorophyll production. Essential for nitrogen assimilation and protein formation.
Molybdenum		Essential for nitrogen assimilation by plants and nitrogen fixation by bacteria. This means that it is needed for the production of nitrogen-based proteins.
Chlorine		Stimulates photosynthesis.
Copper		Activates various enzymes. Also plays a role in chlorophyll production
Zinc		Plays an important role in the synthesis of proteins, enzymes and growth hormones.
Nickel		Key component of selected enzymes involved in N metabolism and biological N fixation.
Beneficial elements	Beneficial elements	Beneficial elements
Silicon		Strengthens cell walls, energy transfer & drought resistance Reduces water loss & prevents fungal infection.
Cobalt		Essential in N fixation
Sodium		Na replaces K in certain functions in halophytes plants For C4 plants having dicarboxylic photosynthetic pathway
Vanadium		Essential for green algae

Forms of elements in Mineral soil

Macro elements are available in (1) Solid (2) Cations (3) Cations in soil solution

Nutrients	Mineral / solid	Cations	Soil solution as ions
N	Organic compounds and Amino acids	NH4 +	NH4 +, NO2 -, NO3 -
P	Organic compounds, nucleic acid and inorganic compounds. Ca, Fe, Al, PO4’s	-	H2PO4 -, HPO4 -
K	Feldspar, mica, silicate clays	K+	K+
Ca	Feldspar, hornblende, lime stone	Ca2+	Ca2+
Mg	Mica, Hornblende, lime stone	Mg2+	Mg2+
S	Organic sources – protein, amino acids inorganic sources – Gypsum, pyrites .	- -	HSO4 -, SO3 2- SO4 2-

Forms of nutrient element absorbed by plants

Nutrient element Forms absorbed

C Mainly through leaves - CO2

H HOH (Hydrogen from H2O) – H [+ ]

2-,,OH-, CO3

O CO2 mainly through leaves – O4

N NH4

K K [+]

+, NO3

Ca Ca [2+ ]

Mg Mg [2+ ]

S SO4

Fe Fe [2+] (Ferrous), Fe [3+] (ferric)

Mn Mn [2+] (Manganous), Mn [4+] (Manganic)

Zn Zn [2+ ]

Cu Cu [+] (cuprous), Cu [2+] (Cupric)

Co CO [2+ ]

Na Na [+ ]

Si Si (OH)4

Cl Cl [-]

B H3BO3 (Boric acid) H2 BO3

(Borate)

Mo Mo O4

References: Tisdale,S.L.,Nelson,W.L.,Beaton,J.D.,Havlin,J.L.1997.Soil fertility and Fertilizers.Fifth edition, Prentice hall of India Pvt.Ltd,New Delhi.

http://edis.ifas.ufl.edu/hs1191

Questions to ponder

1)How will you differentiate between N and K deficiencies of corn visually?

What is luxury consumption?

3)Which element is absorbed both in anionic and cationic forms?

Which element is specifically involved in nitrate reduction in plants?

5)Name the nutrients whos deficiencies are first exhibited in the apical region of the growing plant?

Summary Cheat Sheet

Key Recall Points

Forms of nutrients is exam-relevant for SSAC122 and objective questions in soil science.
Use soil-test based interpretation with focus on pH, CEC, and nutrient availability.
Apply the 4R principle: right source, right rate, right time, and right method.

Exam Traps

Do not mix up soil fertility concepts with fertilizer quantity alone.
Numerical and term-based questions often test definitions, units, and threshold values.
In problem-solving, interpretation must follow soil reaction, crop stage, and management context.

References

3 sources • [1] [2] [3]

[1]

ICAR e-Course: Soil Chemistry, Soil Fertility and Nutrient Management

Official

[2]

Brady and Weil, The Nature and Properties of Soils

Book

[3]

Indian Council of Agricultural Research