1. Soil concepts and characteristics of soils

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 soil60Kg 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