Soil Science Presentation PDF

SOIL SCIENCE (LAT 406) CONCEPTS OF SOIL  Pedology and Edaphology of soil have evolved throuh two centuries of scientific studies  Pedology (scientific study of soil) - considers soil as a natural entity, a biochemically weathered and synthesized product of nature. - It deals with aspec...

SOIL SCIENCE (LAT 406) CONCEPTS OF SOIL  Pedology and Edaphology of soil have evolved throuh two centuries of scientific studies  Pedology (scientific study of soil) - considers soil as a natural entity, a biochemically weathered and synthesized product of nature. - It deals with aspects such as:  origin of the soil, its classification, and its description. Pedologist defines soil as the natural product formed from weathered rocks by the action of climate and living organisms. Edaphology (study of soil from the standpoint of higher plants) - conceive the soil as a natural habitat for plant. - it considers the various properties in relation to plant growth and production Edaphologist may define soil as mixture of mineral and organic matter that is capable of supporting plant life. Soil The origin of the word soil comes from the Latin word solum, which means floor.  The French word sol and the Spanish word suelo are still used to mean either soil or floor. Soil (General definitions)  It is the naturally occurring, unconsolidated or loose covering of weathered/broken rock particles and decaying organic matter (humus) on the surface of the earth, capable of supporting life.  The part of the earth’s surface consisting of humus and disintegrated rock. In general, soil is unconsolidated, or loose combination of inorganic and organic materials supporting life. The inorganic components of the soil are principally the product of rocks and minerals that have been gradually broken down by WEATHER and other NATURAL PROCESSES. The organic materials are composed of debris from PLANTS and from the decomposition of the many tiny life forms that inhabit the soil  SOIL, LAND AND EARTH NB: There is distinction between soil and land. - Whilst soil refers essentially to the synthesized product of weathered rocks (inorganic materials) plus organic matter at different stages of decomposition, including humus - Land includes all conditions of the physical environment of which the soil constitute only one component. Other factors include: i) The underlying geology ii)The hydrology iii)The relief or topography iv)The plant and animal population, and v)The result of human activities – both past and present EARTH - It is one of the eight planets of the universe known to man, which consist of concentric layers of geochemically and geophysically different kinds of materials including water and land masses.  MAJOR COMPONENTS OF SOIL A well formed soil is composed of: i. Organic materials in various stages of decomposition, including humus. ii. Mineral/inorganic particles (matter) iii. Air and iv. Water NB: - The 4 components cannot be separated with much satisfaction because they are present very ultimately mixed with each other. - Physically, the soil consist of stones, large pebbles, dead plants, twigs, roots, leaves and other parts of the plants, fine sand, clay, silt, clay and humus – derived from the decomposition of the organic matter. - The organic and mineral particles are intimately associated in the topsoil. - In the organic matter portion of the soil, about ½ of the total organic matter comprised of dead remains of the soil life in all stages of decomposition and the remaining ½ of the organic matter in the soil is alive ½ (dead remains) Thus, Organic matter ½ (living part) - The living part of the organic matter consist of plant roots, bacteria, earthworms, algae, fungi, nematodes, actinomycetes and many other living organisms. - The mineral particles of the soil can be divided conveniently according to the diameter of the particles. These are: - Clay: < 0.002 mm in diameter. - Silt: between 0.002 – 0.02 mm in diameter. - Sand: between 0.02 – 2.00 mm in diameter NB: VOLUME COMPOSITION OF SOIL - The volume composition of soil in optimum condition for the crop growth are as follows:  mineral matter - 45% solid space  organic matter - 5%  soil water - 25% pore space  soil air - 25% NB: - There are 3 phase system in the soil  the mineral and organic matter form the solid phase.  the water containing salts and some gases in solution, the liquid phase,  the various gases constitute the gaseous phase. Morphological properties (simply referred to as physical properties)  are those which can be detected by sight and feel, NB it is something of an accident that our fingers are not sensitive to pH differences within the range encountered in soils. Analytical properties (simply referred to as Chemical properties)  can be divided broadly into - chemical and - biological properties.  PROPERTIES OF SOIL  Physical (Mechanical)  Chemical  Biological Physical Properties of soil The physical properties of a soil are those characteristics which can be:  seen with the eye or  felt between the thumb and fingers. They are the result of soil parent materials being acted upon by : 1. climatic factors (such as rainfall and temperature), 2. affected by topography (slope and direction), and 3. life forms (kind and amount, such as forest, grass, or soil animals) over a period of time. A change in any one of these influences usually results in a difference in the type of soil formed. PHYSICAL PROPERTIES OF SOIL -It greatly influences its use and behaviour towards plant growth. Thus, plant support, root penetration, drainage, aeration, retention of moisture, and plant nutrients. NB: Physical properties also influence chemical and biological behaviour of all soils Physical properties depend upon: Size of soil, Shape, Arrangement, Mineral composition, Nature, Amount and decomposition of organic matter, Volume and form of pore-space in between soil particles, and Relative amount of air and water present in pore- space. Important physical properties of soils: - Soil colour - Soil texture - Soil structure - Soil density - Soil porosity - Soil consistence - Soil temperature 1. SOIL COLOUR  When soil is examined, colour is one of the first things noticed.  It indicates extremely important soil conditions.  In general, colour is determined by: - organic matter content, - drainage conditions, and - degree of oxidation (extent of weathering).  colour is of no direct agricultural significance, and yet the most easily observed property in soil survey. has no known effect on plant growth  colour is the easily observable characteristic and Important criterion in description and classification of soils Colour of soil is inherited from its parent rock material, which is termed LITHOCHROMIC. Eg. Red soils developed from red sand stone.  Soil colour resulting from soil forming process is termed ACQUIRED or PEDOCHROMIC. Soil colour and Composition Surface soil colours vary from almost white, through shades of brown and grey, to black.  Light colours indicate a low organic matter content  dark colours can indicate a high organic matter content.  Light or pale colours in the surface soil are frequently associated with relatively - coarse texture, - highly leached conditions, and - high annual temperatures. - Dark colours may result from high water table conditions (poor drainage), low annual temperatures, or other conditions that induce high organic matter content and, at the same time, slow the oxidation of organic materials - However, soil colouration may be due to the colours imparted by the parent material. - Shades of red or yellow, particularly were associated with relatively fine textures, usually indicate that subsoil material has been incorporated in the surface layer. - Red, yellowish red and yellow colours are mainly caused by iron products in the clay fraction Colour Indications of Subsoils  Red & Brown coloured - Good Drainage - Red-to-brown colour of subsoils come from iron coatings under well-aerated conditions.  Yellow coloured - Some Drainage  Grey coloured - Poor Drainage 2. SOIL TEXTURE  It refers to the relative proportion/amount of differently sized particles in a given soil. OR the fineness/coarseness of the mineral particles in the soil.  It depends on the relative proportions/ percentage of sand, silt, and clay.  In each textural class there is a range in the amount of sand, silt, and clay that class contains. Classification of soil separates  There are number of systems of naming soil separates. These include: i) The American system developed by United States Department of Agriculture (USDA) ii) The English system, and iii) The International system International system of naming soil separates SOIL SEPARATES DIAMETER RANGE (MM) 1. Coarse sand 2.00 – 0.20 2. Fine sand 0.20 – 0.02 3. Silt 0.02 – 0.002 4. Clay Below 0.002 Soil textured designation ranging from coarse to fine Texture Designation Coarse textured Sand Loamy sand Sandy loam Fine sandy loam Loam Silty loam Silt Silty clay loam Clay loam Fine textured Clay Soil separates: Mineral particles ranges between specified size limits. The names and size limits of major categories of separates recognized in the USA are: SOIL SEPARATION SIZE RANGE FRACTION Very coarse sand 2.0 to 1.0mm Coarse sand 1.0 to 0.5mm Medium sand 0.5 to 0.25mm Fine sand 0.25 to 0.10mm Very fine sand 0.10 to 0.05mm Silt 0.05 to 0.002mm Clay