Saturday, November 1, 2014


Soil is the thin covering over land that consists of a mixture of a mixture of minerals, organic material, living organisms, air and water that support life. The several factors that contribute to formation of soil from parent material are listed below:
-mechanical weathering of rocks due to temperature changes and abrasion
-wind, moving water, glaciers, chemical weathering activities and lichens
-Climate and time are important factors that contribute significantly in the development of soil.
          Extremely cold or dry climate result in slow development of soil
          Humid or warm climates result in rapid formation of soil

Soils are arranged in a series of zones called SOIL HORIZONS
Each horizon has a distinct texture and composition and this varies with different types of soils.
Cross sectional view of horizons in a soil is called SOIL PROFILE
Top layer (surface litter layer) called the 'O' horizon is composed of freshly fallen and partially decomposed leaves, twigs, animal waste, fungi and other organic matter. It is brown or black in colour.
Uppermost layer of soil is called 'A' horizon and it consists of partially decomposed organic matter (humus) and some inorganic mineral particles. It is darker and looser than deeper layers.
Roots of most plants are found in these two upper layers mentioned above.
When these layers are anchored by roots of vegetation, soil stores water and releases it slowly as a trickle.
These layers contain a large amount of bacteria, fungi, earthworms and other small insects that form complex food webs in soil and help recycle soil nutrients thereby contributing to soil fertility.

The 'B' horizon also called subsoil contains less organic material and fewer organisms than 'A' horizon

The area below the subsoil is called'C' horizon and is made-up of weathered parent material. This layer does not contain any organic matter and helps determine the pH of soil. It affects the soiil's rate of water absorption and retention

Soils vary in their content of clay, silt, sand, and gravel. Soils with approximately equal mixtures of clay, silt, sand and humus are called LOAMS.


EROSION: Erosion is defined as movement of surface litter and top soil from one place to another.
-It is a natural process caused by wind and flowing water
-It is accelerated by human activities like farming, construction, overgrazing by livestock, burning of grasses and deforestation
-It reduces fertility of soil and water holding capacity
-It contributes to water pollution
-It clogs lakes
-It increases turbidity of water
-It leads to loss of aquatic life
-If top soil erodes faster that it is formed, the soil becomes a non-renewable resource
-Water and soil are conserved by integrated treatment methods
-The types of treatment are:
-Area treatment and
-Drainage line treatment

EXCESSIVE USE OF FERTILIZERS: The use of chemical fertilizers has increased substantially over the past few decades.
-Fertilizers are valuable as they replace the nutrients used-up by plants
-Primary soil nutrients in short supply are Potassium (K), Phosphorus (P) and Nitrogen (N). They are also called macronutrients
-Boron (B), Zinc (Zn) and Manganese (Mn) are required in small amounts and are called micronutrients.
-When crops are harvested, large amounts of macronutrients and small amounts of micronutrients are removed with crops.
-On growing the same crops again, low amount of nutrients results in decreased yield
-Necessary nutrients are returned to soil by the application of fertilizers.

-Along with fertilizers, pesticides, herbicides, weedicides and fungicides are used to kill unwanted insects, plants and fungi. Rats and mice are killed by rodenticides and plant pests are killed using herbicides.
-Pesticides kill not only pests but also human beings (in sufficiently high doses)
-Persistent pesticides applied once are effective for a long time. They accumulate in the soil and in the bodies of animals in the food chain.
-Biomagnification of persistent pesticides (DDT - half-life = 10 to 15 years)
-Development of insect resistance to insecticides causes farmers to use higher concentration of the same pesticide or use of a different pesticide of higher toxicity
-Pesticides kill beneficial (natural predtors and pollinators) organisms as well as pest species
-Exposure to small quantities of pesticides over several years can cause mutations, cancers, etc.

Alternative agriculture is the broadest term used to describe all non-traditional agricultural methods. This includes:
-sustainable agriculture
-organic agriculture
-alternative methods raising crops
-alternative uses of traditional crops, etc

Irrigated lands produce crop yields much higher than those that use only rain water. Irrigation water contains dissolved salts and in dry climates, the water in the salt solution evaporates leaving salts (NaCl, MgCl2, Na2CO3, etc) in the top soil. The accumulation of salts in soil is called salinization. This leads to:
-stunted plant growth
-low yields
-eventually kill the crop.
Thus, salinization renders the land useless for agriculture.
Salts can be flushed out of soil by using more water. However, this wastes large amounts of water and increases salinity of irrigation water downstream.
If large amounts of water are used to leech salts deep into the soil and drainage is poor, water accumulates underground and gradually raises the water-table covering the roots of plants. This causes the plants to die.

Soil pollution is defined as the introduction of substances, biological organisms or energy into the soil resulting in a change in the quality of soil affecting the normal use of soil or endangering public health and the living environment.

-Accidents involving vehicles transporting waste from site of origin to site of disposal
-Accidents involving vehicles carrying fuel that contaminate the soil when spilled.
-Pollutant might be washed away by precipitation or evaporate if volatile.

Soil pollution is caused by the presence of man-made chemicals or other alteration in the natural soil environment. This type of contamination typically arises from the rupture of underground storage links, application of pesticides, percolation of contaminated surface water to subsurface strata, oil and fuel dumping, leaching of wastes from landfills or direct discharge of industrial wastes to the soil. The most common chemicals involved are petroleum hydrocarbons, solvents, pesticides, lead and other heavy metals. This occurrence of this phenomenon is correlated with the degree of industrialization and intensities of chemical usage.

A soil pollutant is any factor which deteriorates the quality, texture and mineral content of the soil or which disturbs the biological balance of the organisms in the soil. Pollution in soil has adverse effect on plant growth.

Since the metals are not degradable, their accumulation in the soil above their toxic levels due to excessive use of phosphate fertilizers, becomes an indestructible poison for crops.

-Food shortage: Soil pollution leads to water pollution and reduced food production leading to food shortage. This problem is aggravated by population growth.
-Desertification: Continuous exposure of eroded soil to sun for longer periods transforms land into sandy and rocky land. These are symptoms of desertification and render the soil unsuitable for cultivation
-Decrease in extent of agricultural land
-Top soil that is washed away contributes to water pollution by clogging of lakes and increasing turbidity of water leading to loss of aquatic life.
-Fertilizer run-off leads to eutrophication of waterways.

-Proper conservation measures to minimize loss of top soil
-Using Integrated Nutrient Management (INM) and Integrated Pest Management (IPM), bio-pesticides and integrated environment friendly agriculture to reduce dependence on synthetic fertilizers and pesticides.
-Appropriate water management practices in agriculture.
-Keeping soil surface covered with crop residues or crop cover
-Planting trees as part of afforestation
-Using trees as wind breakers or shelter belts
-Undertaking clean-up operations on polluted soils.


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