2. INTRODUCTION
• Soil - covers most of the earth’s land surface
• Soil - natural medium for the growth of plants
• Soils - unconsolidated material of the earth crust in which plants can grow
• According to Joffe (1949) the soil is a natural body of mineral and organic materials
differentiated into horizons
3. CONCEPTS AND VIEW POINTS OF SOIL
• To the mining engineer, the soil is the debris covering the rocks or minerals for
quarry
• To the highway engineer the soil may be the material on which road bed is to be
placed
• To a house owner the soil as seed bed for a flower garden
• To the former soil as a habitat for plants
• To a soil chemist - soil is a store house for planet nutrients
• To geologist soil is weathered rock
• To all of us soil is the source form which produces our food clothing and shelter.
Our existence depends on soil
4. • The word soil comes from the Latin word
• ‘Solum’ means floor. The French word ‘sol’ and Spanish word ‘Suelo’ still used to
mean either ‘soil’ or ‘floor’
• Materials composing the bottom of streams, lakes and ponds are known as
sediments, mud or soil
• The original pond bottom is made of terrestrial soil
• A mixture of solid material and water is called ‘mud’
• Solids settle from the water and cover the pond bottoms with sediment
• Thus, the term sediment after referred to the solids in the pond bottom
5. DEFINITION OF SOIL
• An edaphologist consider “soil as a mixture of mineral and organic matter that is
capable of supporting plant life”
• A pedologist defines “soil as the natural product formed from weathered rock by
the action of climate and living iorganisms”
• The concept of life is vital in this definition
6. MODERN CONCEPT OF SOIL
• Soil - three-dimensional dynamic natural body occurring on the surface of the
earth
• Soil material is properly termed weathered rock and is sometimes called “soil
parent material”
• The word regolith is used as an inclusive term for all the loose material above the
rock bed
The soil
Regolith
Bed rock
7. FUNCTIONS OF SOIL
• It act as natural medium for plant growth
• It provides mechanical support to plants
• It supplies essential nutrients and water to plants.
PARENT MATERIAL
• The consolidated material which is more or less chemically weathered mineral or
organic matter from which the soils is developed by the weathering process
REGOLITH
• Above the bedrock formation there is unconsolidated debris, which is a loose
earth material - regolith
8. SOIL AND MINERAL SOIL
• Soil is different from regolith materials
i. Soil has relatively higher organic matter
ii. It has abundance of plant roots and soil microorganism
iii. It experiences intense weathering
iv. It has characteristic soil horizons and soil profiles
9. SOIL PROFILE
• A vertical section of the soil layers is called soil profile
• The upper layer of the soil contains high organic matter
and darker in color- ‘A horizon or top soil
• The middle part - contains more clay and has a brighter
color than the topsoil - B horizon or Subsoil
• The A and B horizons together are referred to as the
Solum or True Soil
• The C horizon referred to as the soil parent material -
occurs beneath the solum and extends downwards to the
bed rock
10. TOP SOIL OR SURFACE SOIL
• Top soil - major zone of roof development of plants, accumulated with organic
matter
• Is subjected to physical disintegration and chemical decomposition and most
exposed to weathering action
• Topsoil - loose and opens to ensure balanced air and water
11. • Subsoil: The sub soil layer lies underneath the topsoil.
• Bedrock: The solid rock underlines soils and the regolith.
• Mineral soil: A soil usually contains less than 20% of organic matter
• Organic soil: Organic soils contains more than 20% of organic matter
Fig : Composition of an ideal soil (By volume)
12. MAJOR COMPONENTS OF SOIL
Soil has four major components
– Mineral matter
– Organic matter
– Soil water
– Soil air
13. • An ideal soil - 50% solid space and 50% pore space
• Mineral matter and organic matter occupy the total solid space of the soil by about
45% and 5% respectively.
• The total pore space of the soil is occupied by air and water on 50:50
• The proportion of water in the soil will vary under natural conditions depending
upon the weather condition and environmental factors
14. MINERAL SOIL
• An inorganic portion of soil which is variable in size and composition
• Composed of small rock fragments to minerals of various kinds
• Mineral matter - stone, gravel sand, silt and clay
• Stones and gravel - inert - less useful for plant growth
• Clay - chemically active than sand and silt
• The available plant nutrients are stored by the clay and the soil organic matter.
15. ORGANIC COMPONENTS OF SOILS
• Soil organic matter - the partly alive and partly dead and decomposed residues of
plants and animals
• Constitutes 1 and 6% of the topsoil weight
(upland -6%; desert -1%)
• Soils with more than 20 to 30% of organic matter
are called organic soils
16. • Decomposing of organic matter - an important source of phosphorus and sulfur
• Supplies plant nutrients is one of the important functions of organic matter in soil
• Binds mineral particles into soil aggregates providing a more open structure with
adequate pore space for good aeration
• The decomposed organic residues that present in soil are called humus
17. • Water in soil is vital to plant growth - for physiological processes and supplies
plant nutrients in solution
• The amount of water that a soil can store is known as water holding capacity
• Most soil profiles can store between 2.0 and 10.0 inches (5 to 25 cm) of available
water
• Soil water with its dissolved salts called ‘soil solution’
• The water held with in the soil pores is the soil poracity
18. CALCULATION SOIL WATER
Weight of moist soil = 75g
Weight of over dry soil 60Kg
Weight of water presents 15g
Percent of water present 15g x 100= 25%
= 60g
19. SOIL AIR
• Soil air differs from that of the atmosphere
• Soil air is not continuous due to soil composition
• Soil air generally has higher moisture content than the atmosphere
• The carbon dioxide concentration is generally higher than oxygen found in the
atmosphere
• The content and composition of soil air is determined to a large degree by soil
water relationship
20. Generally the soil air occupies the large pores and as the soil dries the pore sizes
decreases
Important gases in the soil are:
• Dissolved oxygen
• Carbon dioxide
• Methane
• Hydrogen Sulfide
• Nitrogen
