Mineral nutrition

1. MINERAL NUTRITION, MANURES AND FERTILIZERS
Mineral nutrition:
It is known that roots of terrestrial plants obtain nourishment
from the soil. It was observed that the plant meet certain
chemical elements refer to as essential elements and that
elements are absorbed by roots as inorganic ions. The process
of absorption, translocation and assimilation of nutrients by
the plants is known as mineral nutrients.
ESSENTIAL ELEMENTS
Plants need 16 elements for their growth and completion of life
cycle. These elements are grouped into two categories as macro
and micro elements. In addition to those 16 essential elements
four more elements viz. sodium, cobalt, vanadium and silicon
are absorbed by some plants for special purposes.

2. Criteria for essentiality:
Arnon and Stout (1939) proposed criteria of essentiality which
was refined by arnon (1954) and element is considered as
essential, when plants cannot complete vegetative or
reproductive stage of life cycle due to its deficiency and this
deficiency can be corrected or prevented only by supplying
that particular element which is directly involved in
metabolism of the plant.
Classification of essential elements:
Elements can be classified based on the amount required,
their mobility in the plants and soil, their chemical nature and
function inside the plant.

3. 1. Basic nutrients: the basic nutrients like C,H,O constitute
96% of total dry matter of plants. Among them, carbon and
oxygen constitute 45% each.
2. Macronutrients:
The nutrients required in large quantities are known as
macronutrients. They are N, P, K, Ca, Mg and S. among
these N,P and K are called primary nutrients Ca, Mg and S
are known as secondary nutrients.
3. Micro nutrients:
The nutrients required in small quantities are known as
micro nutrients or trace elements. They are Fe, Zn, Cu, B,
Mo and Cl. These elements are very efficient and minute
quantities produce optimum effects. On the other hand,
even a slight deficiency in harmful to the plants.

4. Functions in plants:
Based on the functions, nutrients are group into four classes.
1. Elements that provides basic structure to the plant- C,H
and O
2. Elements useful in energy storage, transfer and bonding-
N, S and P
3. Elements necessary for charge balance- K, Ca and Mg
4. Elements involved in enzyme activation and electron
transport- Fe, Mn, Zn, Co, B, Mo and Cl

5. Mobility in soil:
Based on the mobility in soil the nutrient ions can be grouped
as mobile, less mobile and immobile. The mobile nutrients are
highly soluble and are not adsorbed on clay complex eg. NO3
- ,
SO4
= , BO3
=, Cl-, Mn2+ .
Less mobile nutrients are also soluble, but they are adsorbed
on clay complex and so their mobility is reduced.eg. NH4
+
K+ Ca- + Mg2+ Cu2+
Immobile nutrient ions are highly reactive and get fixed in the
soil example H2PO4
-, HPO4
- -
, Zn2+

6. Mobility in plants:
Knowledge of mobility of nutrients in plants helps in finding
what nutrient is deficient. A mobile nutrient in the plant,
moves to the growing points in case of deficiency. Deficiency
symptoms, therefore, appear on the lower leaves.
1. N, P and K are highly mobile
2. Zn is moderately mobile
3. S, Fe, Mn, Cu, Mo and Cl are less mobile
4. Ca and B are immobile.

7. Factors influencing nutrient availability
1. Natural supply of nutrients in the soil which is closely tied up
to parent material of that soil and vegetation under which it is
developed.
2. Soil pH as it affects nutrient release
3. Relative activity of microorganism which play a vital role in
nutrient release and may as in case of micorrhiza directly
function in nutrient uptake.
4. Fertility addition in the form of commercial fertilizer, animal
manure and green manure.
5. Soil temperature, moisture and aeration.

8. TRANSLOCATION
The nutrients absorbed by root hair enter the cortex region
where they are accumulated against the concentration
gradients. From the cortex, they enter xylem vessels and reach
the leaves by mass flow along with transpiration stream. With
regard to nitrogen, a portion of absorbed nitrate- nitrogen (NO3
–N) is reduced to ammonical – nitrogen (NH4 – N) and
glutamine in roots. These compounds along with remaining
portion of NO3 –N passes through the symplast (living
connection between cells) and enters the xylems. From the
xylem vessels, they move upwards by mass flow in the
transpiration stream. They end up in leaves where nitrate
reduction takes place. The reduced compounds enter phloem
vessels and are translocated to growing points like leaves, roots,
fruits etc.

9. ASSIMILATION
Metabolic transformation of inorganic plant nutrient into
organic plants constituents is known as assimilation.
Assimilation laterally means to ‘to make similar’ i.e. the
dissimilar carbon dioxide, water, nitrate etc., are made
similar to compounds found in plants. Carbon dioxide is
metabolically transformed into carbohydrates by
photosynthetic process. Water is assimilated in a few
metabolic reactions, but bulk of it is lost in transpiration.
Some nutrients undergo intensive metabolic transformation
during their conversation from organic form whereas others
do not. A fraction of the absorbed nutrients may be stored in
vacuoles without being assimilated.