Soil Science Important Points Mid Semester II

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Contents :-

Profile soil

Soil pollution

Soil Genesis

Classification of soil water important

Factor affecting of soil water

Soil air important

Humus

Soil organic matter

Soil temperature important and control

Benefit of soil organism and harmful effect . ?

SOIL PROFILE

The soil profile may be defined as a vertical section of soil from the surface down to the hard rock from which the soil is formed (or the vertical section of the soil showing the various layers from the surface to the

unaffected parent material (bed rock) is known as a soil profile).

SOIL POLLUTION

Soil pollution is defined as the presence of toxic chemicals (pollutants or contaminants) in soil, in high enough concentrations to pose a risk to human health and/or the ecosystem.

Causes of Soil Pollution :-

Seepage from landfill .

discharge of industrial waste into soil

Rupture of underground storage tanks

Access application of pesticides herbicides of fertilizers solid wastes

deforestation and soil erosion.

Types of soil Pollution :-

Agriculture soil pollution :-

pollution of surface soil

pollution of underground soil

Agricultural effect of soil pollution :-

Reduce soil fertility

reduced nitrogen fixation

increase erodibility

large loss of soil and nutrients.

Reduce crop yield.

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Classification of soil water :-

Soil water has been classified from a physical and biological point of view as a physical classification of soil water and biological classification of soil water.

Physical classification

Gravitational Water

Gravitational water is free water moving through soil by the force of gravity.

Capillary Water

Capillary water is water held in the micropores of the soil, and is the water that composes the soil solution. Capillary water is held in the soil because the surface tension properties (cohesion and adhesion) of the soil micropores are stronger than the force of gravity.

Hygroscopic Water :-

Hygroscopic water forms as a very thin film surrounding soil particles and is generally not available to the plant.

Biological classification

a. available water

b. unavailable water

C. Super Available water

Importance of soil water ;-

- Water itself act as a principal constituent for plant growth.

- IT act as a solvent

It act a carrier for carrying essential plant.

It regulate soil temperature

It is also control soil forming processes.

It is essential for microbial activity.

Factor affecting soil water ;-

Density of soil :-

Higher the density of soil lower the moisture content.

Temperature:-

Cooler the temperature higher is the moisture retention.

Salt contain :-

More the salt content in the soil less is the water available to the plant.

Organic matter:-

Higher the organic matter more is the water retention in the soil.

There are three main types of soil water -

gravitational water,

capillary water

hygroscopic water

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SOIL GENESIS

Genesis (origin) of soils is a formation of them from mountain rocks and their further (following) development under influence of soil-forming factors in natural and anthropogenic ecosystems of the Earth.

It is absent in the soil-forming rock, and it appears as a result of the soil-forming process.

Soil Air

Air present in between the pore space of soil is called the soil air. This soil air helps in the growth of the aerobic organisms present in the soil.

A well-aerated soil is the one in which gases are available for the growth of plants and the macro or microorganisms present in it.

Definition of soil aeration :

The constant movement of air in the soil mass resulting in the renewal of gases is known as soil aeration

Composition of soil air :-

Soil air contains gases like nitrogen, oxygen, carbon dioxide, water vapour and

others.The composition of soil air is different from atmospheric air. Soil air contains more

carbon dioxide and less oxygen than atmospheric air

Importance of soil air in plant growth and biological activities in soil ;-

1.)

Growth of plants and the development of roots :

The growth of plants are adversely affected by poor aeration namely.

2.)

Adaptations of plant :

The ability of different plant species to grow in soils with low soil air porosity varies greatly.

3.) Microorganisms population and activity :

The microorganisms living in the soil also

require oxygen for respiration and metabolism.

4.) Formation of toxic material :

Poor aeration results in the development of toxin and other injurious substances such as ferrous oxides, H2S, Gas, CO2 gas etc., in the soil.

Factors Affecting Soil Aeration

Amount of air space:

Soil organic matter:

Soil moisture

Seasonal differences

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HUMUS

Humus is dark, organic material that forms in soil when plant and animal matter decays.

The thick brown or black substance that remains after most of the organic litter has decomposed is called humus.

What do you mean by Soil Organic Matter?

Soil organic component of soil, consisting of three primary parts including

small (fresh) plant residues

and small living soil organisms,

decomposing (active) organic matter,

and stable organic matter (humus).

Soil organic matter (SOM) is the portion of soil that is composed of living and dead things in various states of decomposition, such as plant roots and microbes.

SOIL TEMPERATURE🌡️

Soil temperature is simply the measurement of the warmth in the soil.

Soil temperature is the factor that drives germination of seeds. Soil temperature directly affects plant growth. Most soil organisms function best at an optimum soil temperature. (18-24 C.).

Importance of Soil Temperature:

1. In affects plant growth directly, that is all crops practically slow down their growth below the soil temperature of about 90C and above the soil temperature of above 50 0C.

2. For germination of different seeds requires different ranges of soil temperature e.g. maize begins to germinate at soil temp of 7 to 100C.

3. Most of the soil organisms function best at an optimum soil temperature of 25 to 350C

4. The optimum soil temperature for nitrification is about 320C.

5. It also influences soil moisture content, aeration and availability of plant nutrients.

Controlling Soil Temperature -

Effect of soil temperature on plant growth. Plants grow best in a certain range of temperatures.

Mulch. Mulch acts as an insulation.

Compaction. Loose soil contains air spaces that insulate the soil, acting a little like a much.

Moisture. Water in the soil conducts heat rapidly.

Benefits of Microbes in Soil :-

Decompose organic matter.

Foster soil aggregate stability.

Recycle and regulate carbon, nitrogen and phosphorous.

Fix nitrogen for plant uptake.

Increase the available plant root area for nutrient uptake.

Degrade pesticides.

Improve soil structure.

Help control diseases.

Harmful effect of soil organisms :-

Some soil fauna such as snails and slugs damage and destroy crops.

Ants transfer aphids to certain crops.

Some crop roots are infested with nematodes sometimes seriously enough to affect the growth of these crops adversely.