Soil as a natural resource

Soil is considered to be the “skin of the earth". Soil is capable of supporting plant life and all life on earth. Soils are complex mixtures of 5 major components. The importance of soils as natural resource are highlighted in this module.

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SOIL AS A NATURAL RESOURCE


by
Prof. A. Balasubramanian
Centre for Advanced Studies in Earth Science
University of Mysore
India

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The Skin of mother Earth:
Soil is considered to be the “skin of the
earth".

It is formed as a product of weathering from
various parent rocks or as transported
materials from far off places by the action of
water, wind, glaciers and other agents.

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Soil is capable of supporting plant life and all
life on earth.

Soil is an unconsolidated heterogenous,
mineral or organic natural medium, suitable
for the growth of natural vegetation and
crops.

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Soils are complex mixtures:
Soils are complex mixtures of 5 major
components. They are:
1. minerals,
2. water,
3. air,
4. organic matter, and
5. countless living organisms( microbial
life).

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Soils are loose mineral masses:
Soils are the loose mineral or organic
materials found on the earth's surface,
usually (or averagely) made up of about 25%
air, 25% water, 45% mineral and 5% organic
matter (humus, tiny living organisms and
sometimes plant residue).

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Pedology:
The scientific study of soils, particularly their
formation, morphology, distribution and
classification is called as Pedology.
Pedogenesis:
It is a branch which deals with the origin and
formation processes of soils and their
morphological characters.

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The soil is at the interface between
various spheres of the earth:
The soil is at the interface between the
atmosphere , lithosphere , hydrosphere and
biosphere.
Soils have been used for cultivation
intensively for at least 5500 years. About
2000 years ago some crude soil fertility
relationships were also proposed for crops.

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Because soil is important for cultivation and
agricultural production, soil fertility and
productivity are important issues to address.

Soil is always under the dynamic
influence of environmental factors:
This unconsolidated surface layer of the
earth is subjected to the action of various
environmental factors.

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The notable factors are:
1) climate (including water and temperature
effects), and
2) macro- and microorganisms,
conditioned by relief, acting on the parent
rocks over a period of time.

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Importance (Functions) of soils:
Soil performs 7 major functions in almost
many ecosystems:
They are:
1. Soils serve as a medium for the growth
of all kinds of plants.
2. Soils modify the atmosphere by emitting
and absorbing gases (carbon dioxide,
methane, water vapor, and the like) and
dust.

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3. Soils provide a suitable habitat for
animals that live in the soil (such as
groundhogs and mice) to organisms (such
as bacteria and fungi), that account for
most of the living things on Earth.
4. Soils absorb, hold, release, alter, and
purify most of the water received from
precipitation and snow melt, on land.

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5. Soils process recycled nutrients,
including carbon, so that living things can
use them over and over again.
6. Soils serve as engineering media for
construction of foundations, roadbeds,
dams and buildings, and artifacts of
human use.
7. Soils act as a living filter to clean water
before it moves into an aquifer.

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Soils and the earth's cyclic processes:
Soils play a dominant role in earth's
geomorphic processes in a cyclic manner.
The role of soil is prominent in
a) rock cycle,
b) geomorphic cycle
c) hydrologic cycle
d) geochemical cycles
e) Biogeochemical cycles and
f) Nutrient Cycles.

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Soils are characterised by many
properties:
In addition to the 5 major components, soils
are characterised by various
physical,
chemical,
engineering and
biological properties.

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They are:
(A) the following Physical Properties of soils:
(1) Soil separates and texture,
(2) Structure of soil,
(3) Weight and soil density,
(4) Porosity of soil,
(5) Permeability of soil,
(6) Soil colour,
(7) Temperature of soil, and

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(8) Engineering properties like Soil
Plasticity, Compressibility and Erodibility.
(B) Chemical Properties of Soils, including:
(1) Inorganic matters of soil,
(2) Organic matters in soil,
(3) Colloidal properties of soil particles,
and
(4) Soil reactions and Buffering action,
(5) Acidity/ Alkalinity/ salinity/ sodicity

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C) Soil moisture

D) Soil Profile( vertical distribution of soil
horizons)

E) Soil Air

F) Soil Morphology.

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Importance of Soils:

1. Soils are ecosystems:
Soils are a host of small, medium, and large
organisms.
Many mammals, birds, insects, and protozoa
live in soils. But the greatest biodiversity lies
in the soil microbes — the bacteria, fungi,
and archaea.

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A teaspoon of rich soil can contain one billion
bacteria.
Soil microbiologists apply advanced
molecular techniques to understand the
diversity and function of soil microbes.
It is an interesting field of exploration with
new biological taxa in soils.

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2. Soils are Need for plant growth:

Soils are the primary provider of nutrients
and water for much of the plant life on earth.
There are 18 elements considered essential
for plant growth, most of which are made
available to plants through root uptake from
soils.

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Soils retain nutrients:
Soils retain nutrients by several mechanisms.
Most nutrients are dissolved in soil water as
either positively or negatively charged ions;
soil particles are also charged and thereby
are able to electrically hold these ions.
Soils also hold nutrients by retaining the soil
water itself.

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3. Soils are Clay Factories:

Clay and silt particles are the primary
mineral components in soils that retain
water — these small particles slow the
drainage of water and, like a sponge,
physically hold water through capillary
forces.

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Clay provides such strong force that plants
can't pull all the water away from it, which
makes silt particles the ultimate ingredient
for plant-available water storage.

Among the most important functions
performed by soils is to provide the ideal
conditions for clay synthesis.

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Clays are chemically reactive with ions,
water, and other particles. These reactions
are critical for the provision of many
ecosystem services.
Clays are often the most active mineral
particles. They have unique chemical
characteristics like much surface area which
makes them a hot spot for chemical
reactions.

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4. Soils are Service Providers:

Soils are the among the great ecosystem
service providers on earth.
They store and provide water for plants.
They prevent floods by transferring water
slowly to streams and groundwater.
They filter and remediate pollutants.

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Soils cycle and recycle nutrients :
Soils cycle and recycle nutrients and wastes
— transforming them into biologically
available forms,
---storing them away for later use, and
---preventing their leaching to ground and
surface waters.
Soils provide habitat for a vast diversity of
life.

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Soils take up and release important gases,
including oxygen and greenhouse gases, a
service called gas regulation.

5. Medium for plant growth:

Soils support roots and keep them upright
for growth.
Soils provide plants with essential minerals
and nutrients.

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Soils provide air for gaseous exchange
between roots and atmosphere.
Soils protect plants from erosion and other
destructive physical, biological and chemical
activity.
Soils hold water (moisture) and maintain
adequate aeration.

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6. Habitat for many insects and other
organisms:
Insects and microbes (very tiny single celled
organisms) live in the soils and depend on
soils for food and air.
Soils are homes to a diverse range of
organisms such as worms and termites.
They provide the needed moisture and air
for breakdown of organic matter.

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They provide a home for many organisms
such as insects to lay and hatch eggs and
rodents to give birth to new off springs.

7. Filtration system for surface water:
After rainfall and snowmelts, water flows on
the earth’s surface to water bodies, but much
of it soaks and gets infiltrated into the
ground.

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As it continues its way downwards through
the many layers in the ground, it is filtered
from dust, chemicals and other
contaminants.
This is why aquifers (underground water)
are one of the purest sources of water.
Filtered water also provides plants with
clean, unpolluted water needed for growth.

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8. Carbon store and maintenance of
atmospheric gases:
Soils help regulate atmospheric Carbon
dioxide by acting as a carbon store.
During humification (a process where soil
organisms form complex and stable organic
matter) some organic matter breakdown do
not occur completely, especially in soils like
peat, owing to its high acid and water
content.

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On a global scale, soils contain about twice as
much carbon as the atmosphere and about
three times as much as vegetation .
This results in the accumulation of organic
matter in the soil which are high in carbon
content.
Nitrogen, phosphorus, and many other
nutrients are stored, transformed, and cycled
in the soil.

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9. Soils may get degraded and Polluted:

Many human activities degrade and pollute
soils.
Erosion is among the great causes of soil
degradation.
Salinization and desertification are major
causes of soil degradation in arid areas.

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Salinization is the buildup of salts in soils to
a point that they destroy the physical and
chemical properties of soil and make it
impossible for plants to take up water from
the soil.
Salinization is often associated with
improper irrigation.
Desertification is caused by a combination
of climate changes and human-induced soil
degradation(such as through overgrazing).

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Soils have a great capacity to filter
and remediate pollutants, but applications
of pollutants to soils often exceed this
capacity.

10. Human Pressure on Soils:
The increasing human population is placing
greater pressure on soil and water resources
and threatening our ability to produce
sufficient food, feed, and fiber.

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As a result, there is a growing consensus
within our global community that the
protection of natural resources and
implementation of environmentally and
economically sound agriculture practices is
of the utmost priority.

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TYPES OF SOILS:
There are many types of soils, usually placed
in classes (types) based on their color,
profile, texture, composition or structure.
Each soil type is formed differently, and can
be found in specific places on the earth’s
immediate surface, mid and deep under the
surface.
Sand, silt, and clay are the basic particles in a
soil.

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Most soils are made up of a combination of
the three.
The texture of the soil, how it looks and
feels, depends upon the amount of each
particle in that particular soil.

The type of soil varies from place to place on
our planet and can even vary from one place
to another in your own backyard.

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Importance of Soil Conservation:

Soil erosion, caused by wind and rain, can
change land by wearing down mountains,
creating valleys, making rivers appear and
disappear.
It is a slow and gradual process that takes
thousands, even millions of years.

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But erosion may be speeded up greatly by
human activities such as farming and mining.

Soil develops very slowly over a long period
of time but can be lost very quickly.

The clearing of land for farming, residential,
and commercial use can quickly destroy soil.

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It speeds up the process of erosion by
leaving soil exposed and also prevents
development of new soil by removing the
plants and animals that help build humus.