CSP202 (Basic Soil Science) Past Paper PDF

CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE Lecturer in Charge: 1. Prof. B. S. Ewulo 2. Dr. A. J. Adeyemo 3. Dr. S.A. Adejoro 4. Miss O. Akingbola SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BA...

CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE Lecturer in Charge: 1. Prof. B. S. Ewulo 2. Dr. A. J. Adeyemo 3. Dr. S.A. Adejoro 4. Miss O. Akingbola SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE CONTENTS 1.0 ROCK 1.1 Rock Definition, Type and Properties 1.2 Rock minerals 1.3 Rock Weathering 1.3.1 Mechanical or physical weathering 1.3.2 Chemical weathering 2.0 SOIL FORMATION 2.1 Three Functions of Soil 2.2 Factors of Soil Formation 2.3 Soil Forming Processes 2.3.1 Simple Processes of Pedogenesis 2.3.2 Specific soil forming processes 2.4 Soil Profile 2.4.1 Master Horizon and its Designation 2.4.2 Suffixes to the Master Horizon Symbols 3.0 SOIL PHYSICAL PROPERTIES 3.1 Soil Texture 3.1.1 Importance of soil texture 3.2 Soil Structure 3.2.1 Types of soil structure 3.3 Soil Bulk Density 3.4 Soil Consistence 3.5 Soil Porosity 3.5.1 Determination of Total Soil Porosity SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE 3.5.2 Determination of Micro porosity 3.5.3 Determination of Macro Porosity 3.6 Soil Water 3.6.1 Determination of gravimetric moisture content 3.7 Soil Temperature 4.0 Soil Chemistry 4.1 Soil pH 4.2 Cation exchange 4.3 cation exchange capacity 4.3.1 Importance of Cation exchange capacity 4.3.2 Factors affecting cation exchange capacity 4.4 Base saturation 5.0 Soil Organism 5.1 Higher plants 5.2 Bacteria 5.3 Nitrogen-Fixing Bacteria 5.4 Fungi 5.5 Algae 5.6 Lichen 5.7 Arthropods 5.8 Nematode 6.0 Soil Classification 6.1 Types of Classification 6.2 USDA Soil Taxonomy ‘7th approximation’ SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE 6.2.1 Hierarchy of Categories in the Soil Taxonomy 6.3 FAO Classification system SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE 1.0 ROCK 1.1 ROCK DEFINITION, TYPE AND PROPERTIES Soil is formed from the weathering and disintegration of rock. A rock is an indefinite mixture of naturally occurring substances, mainly minerals. There are three major types of rock, namely; 1) igneous, 2) sedimentary and 3) metamorphic rock. The usual classification of rocks by geologist is genetic, relating to their modes of origin, and includes the following groups: (a) Igneous rocks formed from ascending hot liquid material arising deep in the Earth called magma which crystallizes into the solid state as the temperature falls. (b) Sedimentary rocks formed as a result of accumulation and compaction of: (i) pre-existing rock fragments disintegrated throughout erosive processes; (ii) organic debris such as shells; (iii) materials dissolved in surface of groundwater and later precipitated in conditions of oversaturation; (c) Metamorphic rocks formed from any pre-existing rock subjected to increases in pressure or temperature or both. Table 1: Major Rock Types, Their Origin and Properties Rock type Origin Example Properties Igneous Cooling of magma Granite basalt Light colour coarse grained dark colour fine grained Sedimentary Deposition and Shale Any colour, fined compaction Sandstone grained Any colour, limestone coarse grained Light coloured, shells or caco3 present Metamorphic Charge in igneous or Slate Any colour, hardened sedimentary marble shale Any colour, changed limestone SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE The rate and extent of rock weathering depends on; 1) the chemical composition of the minerals that comprise the rock or sediment, 2) the type, strength, and durability of the material that holds the mineral grains together, 3) the extent of rock flaws or fractures, 4) the rate of leaching through the material, and 5) the extent and type of vegetation at the surface 1.2 ROCK MINERALS The earth is composed of various kinds of elements. These elements are in solid form in the outer layer of the earth and in hot and molten form in the interior. The elements in the earth’s crust are rarely found exclusively but are usually combined with other elements to make various substances. These substances are recognized as minerals. Mminerals are therefore naturally occurring organic and inorganic substances, having an orderly atomic structure and a definite chemical composition and physical properties. A mineral is composed of two or more elements. But, sometimes single element minerals like sulphur, copper, silver, gold, graphite etc are found. Approximately 98 percent of the mass of the earth's crust is composed of eight elements like oxygen, silicon, aluminium, iron, calcium, sodium, potassium and magnesium (see table below) and the rest is constituted by titanium, hydrogen, phosphorus, manganese, sulphur, carbon, nickel and other elements. SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE Table 2: Elements of the Earth Crust Oxygen and silicon, compose 75 percent of it. Many of the elements important in the growth of plants and animals occur in very small quantities. Obviously, these elements and their compounds are not evenly distributed throughout the earth's surface. In some places, for example, phosphorus minerals (apatite) are so concentrated that they are mined; in other areas, there is a deficiency of phosphorus for plant growth. Most elements of the earth's crust have combined with one or more other elements to form the minerals. The minerals generally exist in mixtures to form rocks, such as the igneous rocks, granite and basalt. The mineralogical composition of igneous rocks, and the sedimentary rocks, shale and sandstone, are given in Table below; SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE Table 3: Mineralogical Composition of Rocks Primary minerals weathers to form secondary minerals. The weathering products of some minerals are given in the table below; Table 4: Weathering Product of Some Minerals SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE 1.3 ROCK WEATHERING Two classifications of weathering processes exists; 1) Mechanical or physical weathering, and 2) chemical weathering. However, chemical and physical weathering often goes hand in hand. For example, cracks exploited by mechanical weathering will increase the surface area exposed to chemical action. Furthermore, the chemical action at minerals in cracks can aid the disintegration process..1.3.1 Mechanical or physical weathering Mechanical or physical weathering involves the breakdown of rocks and soils through direct contact with atmospheric conditions such as heat, water, ice and pressure. (i) Thermal expansion Thermal expansion, also known as onion-skin weathering, exfoliation, insolation weathering or thermal shock, often occurs in areas, like deserts, where there is a large diurnal temperature range. The temperatures soar high in the day, while dipping greatly at night. As the rock heats up and expands by day, and cools and contracts by night, stress is often exerted on the outer layers. The stress causes the peeling off of the outer layers of rocks in thin sheets. Though this is caused mainly by temperature changes, thermal expansion is enhanced by the presence of moisture. (ii) Freeze thaw weathering This process can also be called frost shattering. This type of weathering is common in mountain areas where the temperature is around freezing point. Frost induced weathering, although often attributed to the expansion of freezing water captured in cracks, is generally independent of the water-to-ice expansion. It has long been known that moist soils expand or frost heave upon freezing as a result of water migrating along from unfrozen areas via thin films to collect at growing ice lenses. This same phenomena occurs within pore spaces of rocks. They grow larger as they attract liquid water from the surrounding pores. The ice crystal growth weakens the rocks which, in time, break up. The phenomenon is caused by the almost unique property of water in having its greatest density at 4 C, so ice is of greater volume than water at the same SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE temperature. When water freezes, then it expands and puts its surroundings under intense stress. Freeze induced weathering action occurs mainly in environments where there is a lot of moisture, and temperatures frequently fluctuate above and below freezing point—that is, mainly alpine and periglacial areas. An example of rocks susceptible to frost action is chalk, which has many pore spaces for the growth of ice crystals. When water that has entered the joints freezes, the ice formed strains the walls of the joints and causes the joints to deepen and widen. This is because the volume of water expands by 9% when it freezes. When the ice thaws, water can flow further into the rock. When the temperature drops below freezing point and the water freezes again, the ice enlarges the joints further. Repeated freeze- thaw action weakens the rocks which, over time, break up along the joints into angular pieces. The angular rock fragments gather at the foot of the slope to form a talus slope (or scree slope). The splitting of rocks along the joints into blocks is called block disintegration. The blocks of rocks that are detached are of various shapes depending on rock structure. (iii) Pressure release In pressure release, also known as unloading, overlying materials (not necessarily rocks) are removed (by erosion, or other processes), which causes underlying rocks to expand and fracture parallel to the surface. Often the overlying material is heavy, and the underlying rocks experience high pressure under them, for example, a moving glacier. Pressure release may also cause exfoliation to occur. Intrusive igneous rocks (e.g. granite) are formed deep beneath the earth's surface. They are under tremendous pressure because of the overlying rock material. When erosion removes the overlying rock material, these intrusive rocks are exposed and the pressure on them is released. The outer parts of the rocks then tend to expand. The expansion sets up stresses which cause fractures parallel to the rock surface to form. Over time, sheets of rock break away from the exposed rocks along the fractures. Pressure release is also known as "exfoliation" or "sheeting" SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE (iv) Hydraulic action This is when water (generally from powerful waves) rushes into cracks in the rock face rapidly. This traps a layer of air at the bottom of the crack, compressing it and weakening the rock. When the wave retreats, the trapped air is suddenly released with explosive force. The explosive release of highly pressurized air cracks away fragments at the rockface and widens the crack itself. (v) Salt weathering Salt crystallization causes disintegration of rocks when saline solutions seep into cracks and joints in the rocks and evaporate, leaving salt crystal behind. These salt crystals expand as they are heated up, exerting pressure on the confining rock. Salt crystallization may also take place when solutions decompose rocks (for example, limestone and chalk) to form salt solutions of sodium sulfate or sodium carbonate, of which the moisture evaporates to form their respective salt crystals. The salts which have proved most effective in disintegrating rocks are sodium sulfate, magnesium sulfate, and calcium chloride. Some of these salts can expand up to three times or even more. It is normally associated with arid climates where strong heating causes strong evaporation and therefore salt crystallisation. 1.3.2 Chemical weathering Chemical weathering involves the direct effect of atmospheric chemicals, or biologically produced chemicals (also known as biological weathering). Living organisms may contribute to mechanical weathering (as well as chemical weathering). Lichens and mosses grow on essentially bare rock surfaces and create a more humid chemical microenvironment. The attachment of these organisms to the rock surface enhances physical as well as chemical breakdown of the surface microlayer of the rock. On a larger scale seedlings sprouting in a crevice and plant roots exert physical pressure as well as providing a pathway for water and chemical infiltration. Burrowing animals and insects disturb the soil layer adjacent to the bedrock surface thus further increasing water and acid infiltration and exposure to oxidation processes. SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE The most common form of biological weathering is the release of chelating compounds, i.e acids, by plants so as to break down aluminum and iron containing compounds in the soils beneath them. Decaying remains of dead plants in soil may form organic acids which, when dissolved in water, cause chemical weathering. Chemical weathering involves the change in the composition of rocks, often leading to a 'break down' in its form. This is done through a combination of water and various chemicals to create an acid which directly breaks down the material. This type of weathering happens over a period of time. (i) Dissolution Rainfall is acidic because atmospheric carbon dioxide dissolves in the rainwater producing weak carbonic acid. In unpolluted environments, the rainfall pH is around 5.6. Acid rain occurs when gases such as sulphur dioxide and nitrogen oxides are present in the atmosphere. These oxides react in the rain water to produce stronger acids and can lower the pH to 4.5 or even 3.0. Sulfur dioxide, SO2, comes from volcanic eruptions or from fossil fuels, can become sulfuric acid within rainwater, which can cause solution weathering to the rocks on which it falls. (ii) carbonation One of the most well-known solution weathering processes is carbonation, the process in which atmospheric carbon dioxide leads to solution weathering. Carbonation occurs on rocks which contain calcium carbonate such as limestone and chalk. This takes place when rain combines with carbon dioxide or an organic acid to form a weak carbonic acid which reacts with calcium carbonate (the limestone) and forms calcium bicarbonate. This process speeds up with a decrease in temperature and therefore is a large feature of glacial weathering. The reactions as follows: CO2 + H2O = H2CO3 carbon dioxide + water -> carbonic acid H2CO3 + CaCO3 = Ca(HCO3)2 Carbonic acid + calcium carbonate = calcium bicarbonate Carbonation on the surface of well-jointed limestone produces a dissected limestone pavement which is most effective along the joints, widening and deepening them. SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE (iii) Hydration Mineral hydration is a form of chemical weathering that involves the rigid attachment of H+ and OH- ions to the atoms and molecules of a mineral. When rock minerals take up water, the increased volume creates physical stresses within the rock. For example iron oxides are converted to iron hydroxides and the hydration of anhydrite forms gypsum. (iv) Hydrolysis Hydrolysis is a chemical weathering process affecting Silicate minerals. In such reactions, pure water ionizes slightly and reacts with silicate minerals. An example reaction: Mg2SiO4 + 4H+ + 4OH- = 2Mg2+ + 4OH- + H4SiO4 olivine (forsterite) + four ionized water molecules = ions in solution + silicic acid in solution This reaction results in complete dissolution of the original mineral, assuming enough water is available to drive the reaction. However, the above reaction is to a degree deceptive because pure water rarely acts as a H+ donor. Carbon dioxide, though, dissolves readily in water forming a weak acid and H+ donor. Mg2SiO4 + 4CO2 + 4H2O = 2Mg2+ + 4HCO3- + H4SiO4 olivine (forsterite) + carbon dioxide + water = Magnesium and bicarbonate ions in solution + silicic acid in solution This hydrolysis reaction is much more common. Carbonic acid is consumed by silicate weathering, resulting in more alkaline solutions because of the bicarbonate. This is an important reaction in controlling the amount of CO2 in the atmosphere and can affect climate. Aluminosilicates when subjected to the hydrolysis reaction produce a secondary mineral rather than simply releasing cations. 2KAlSi3O8 + 2H2CO3 + 9H2O = Al2Si2O5(OH)4 + 4H4SiO4 + 2K+ + 2HCO3- Orthoclase (aluminosilicate feldspar) + carbonic acid + water = Kaolinite (a clay mineral) + silicic acid in solution + potassium and bicarbonate ions in solution (v) Oxidation Within the weathering environment chemical oxidation of a variety of metals occurs. The most commonly observed is the oxidation of Fe2+ (iron) and combination with oxygen and water to SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE form Fe3+ hydroxides and oxides such as goethite, limonite, and hematite. This gives the affected rocks a reddish-brown coloration on the surface which crumbles easily and weakens the rock. This process is better known as 'rusting'. SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE 2.0 SOIL FORMATION Everything that affects formation, development, characteristics and geographic distribution of soils belongs to soil-forming factors. That´s why the Earth´s soil cover is very diverse. Impact of soil-forming factors results in soil forming processes. 2.1 Three Functions of Soil (i) Provides a medium for plant growth (ii) Regulates and partitions water flow through the environment (iii) Serves as an environmental filter 2.2 Factors of Soil Formation Dokuchaiev (1889) established that the soils develop as a result of the action of soil forming factors S = f (P, Cl, O) Further, Jenny (1941) formulated the following equation S = f (Cl, O, R, P, T, …) Where, Cl – environmental climate O – Organisms and vegetation (biosphere) R – Relief or topography P – Parent material T- Time … - additional unspecified factors The five soil forming factors, acting simultaneously at any point on the surface of the earth, to produce soil. (i) CLIMATE Climate is the most significant factor controlling the type and rate of soil formation. The dominant climates recognized are: SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE  Arid Climate: The precipitation here is far less than the water-need. Hence the soils remain dry for most of the time in a year.  Humid climate: The precipitation here is much more than the water need. The excess water results in leaching of salt and bases followed by translocation of clay colloids.  Oceanic climate: Moderate seasonal variation of rainfall and temperature.  Mediterranean climate: The moderate precipitation. Winters and summers are dry and hot.  Continental climate: Warm summers and extremely cool or cold winters.  Temperate climate: Cold humid conditions with warm summers.  Tropical and subtropical climate: Warm to hot humid with isothermal conditions in the tropical zone. Climate affects the soil formation directly and indirectly. Directly, climate affects the soil formation by supplying water and heat to react with parent material. Indirectly, it determines the fauna and flora activities which furnish a source of energy in the form of organic matter. This energy acts on the rocks and minerals in the form of acids, and salts are released. The indirect effects of climate on soil formation are most clearly seen in the relationship of soils to vegetation. Precipitation and temperature are the two major climatic elements which contribute most to soil formation. (a) Precipitation Precipitation is the most important among the climatic factors. As it percolates and moves from one part of the parent material to another. It carries with it substances in solution as well as in suspension. The substances so carried are re deposited in another part or completely removed from the material through percolation when the soil moisture at the surface evaporates causing an upward movement of water. The soluble substances move with it and are translocated to the upper layer. Thus rainfall brings about a redistribution of substances both soluble as well as in suspension in soil body. SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE (b) Temperature Temperature is another climatic agent influencing the process of soil formation.  High temperature hinders the process of leaching and causes an upward movement of soluble salts.  High temperature favors rapid decomposition of organic matter and increase microbial activities in soil while low temperatures induce leaching by reducing evaporation and there by favour the accumulation of organic matter by slowing down the process of decomposition. Temperature thus controls the rate of chemical and biological reactions taking place in the parent material. Jenney (1941} computed that in the tropical regions the rate of weathering proceeds three times faster than in temperate regions and nine times faster than in arctic. Chemical and biological reaction rates double for every 10 ºC increase (ii) ORGANISMS AND VEGETATION (BIOSPHERE) (a) ORGANISM The active components of soil ecosystem are plants, animals, microorganisms and man. The role of microorganisms in soil formation is related to the humification and mineralization of vegetation. The action of animals especially burrowing animals to dig and mix-up the soil mass and thus disturb the parent material Man influences the soil formation through his manipulation of natural vegetation, agricultural practices etc. Compaction by traffic of man and animals decrease the rate of water infiltration into the soil and thereby increase the rate of runoff and erosion. (b) VEGETATION The roots of the plants penetrate into the parent material and act both mechanically and chemically. They facilitate percolation and drainage and bring about greater dissolution of minerals through the action of CO2 and acidic substances secreted by them. The decomposition and humification of the materials further adds to the solubilization of minerals SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE Forests – reduces temperature, increases humidity, reduce evaporation and increases precipitation. Grasses reduce runoff and result greater penetration of water in to the parent material. (iii) RELIEF OR TOPOGRAPHY The relief and topography sometimes are used as synonymous terms. They denote the configuration of the land surface. The topography refers to the differences in elevation of the land surface on a broad scale. The prominent types of topography designations, as given in FAO Guidelines (1990) are: Land Surface with slopes of 1 Flat to Almost flat 0–2% 2 Gently undulating 2-5% 3 Undulating 5 – 10 % 4 Rolling 10 – 15 % 5 Hilly 15 –3 0 % 6 Steeply dissect > 30 % with moderate range of elevation ( 30% with great range of elevation (>300 m) (a) Soil formation on flat to almost flat position On level topographic positions, almost the entire water received through rain percolates through the soil. Under such conditions, the soils formed may be considered as representative of the regional climate. They have normal solum with distinct horizons. But vast and monotonous level land with little gradient often has impaired drainage conditions. (b) Soil formation on undulating topography The soils on steep slopes are generally shallow, stony and have weakly- developed profiles with less distinct horizonation. It is due to accelerated erosion, which removes surface material before it has the time to develop. Reduced percolation of water through soil is because of SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE surface runoff, and lack of water for the growth of plants, which are responsible for checking of erosion and promote soil formation. (c) Soil formation in depression The depression areas in semi-arid and sub humid regions reflect more moist conditions than actually observed on level topographic positions due to the additional water received as runoff. Such conditions favour more vegetative growth and slower rate of decay of organic remains. This results in the formation of comparatively dark- coloured soils rich in organic matter (Mollisols). (d) Soil formation and Exposure Aspect Topography affects soil formation by affecting temperature and vegetative growth through slope exposures (aspect}. The southern exposures (facing the sun) are warmer and subject to marked fluctuations in temperature and moisture. The northern exposures, on the other hand are cooler and more humid. The eastern and western exposures occupy intermediate position in this respect. (iv) PARENT MATERIALS Parent materials can vary from solid rock to deposits like alluvium and boulder clay. It has been defined as ‘the initial state of the soil system’, the mass (consolidated material) from which the soil is formed. The parent material can influence or impact soil in a number of ways namely; 1) c olour, 2) texture, 3) mineral composition, 4) permeability/drainage, 5) pH, 6) innate soil fertility Parent materials are classified into two groups namely; a) Residual parent materials b) Transported parent materials (a) Residual parent materials – Soils develop from underlying bedrock (Igneous, sedimentary, metamorphic) insitu. The parent material differ as widely as the rocks. Type of rock strongly influences type of soil i.e – Limestone → clayey soils, – Sandstone → coarse, acidic soils, – Granite → coarse, acidic soils, – Slate, shale → clayey soils SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE (b) Transported parent materials – soils develop on transported parent materials, the materials are distinguished according to its mode of transportation viz;  Colluvial debris  Alluvial deposits  Marine sediments  Lacustrine sediments  Eolian deposits  Glacial deposits (i) Colluvial Massive to moderately well stratified, nonsorted to poorly sorted sediments with any range of particle sizes from clay to boulders and blocks that have reached their present position by direct, gravity-induced movement. They are restricted to products of mass-wasting whereby the debris is not carried by wind, water, or ice (except snow avalanches). (ii) Alluvial deposits Transport by water on land produces alluvial, terrace and footslope deposits, during flooding, water spreads and slows, and fine sediment is deposited. Usually very fertile soils and important for agriculture, forestry, wildlife, poor choice for homes and other urban development (iii) Marine sediments marine deposits under the sea. Sediments build up over time, Exposed by changes in elevation of earth’s crust, materials are gravely, sandy, clayey depending on area. (iv) Lacustrine sediments Descriptive of materials that have either settled from suspension in bodies of standing fresh water or have accumulated at their margins through wave action. Sediments generally consisting of either stratified fine sand, silt, and clay deposited on the lake bed; or moderately well sorted and stratified sand and coarser materials that are beach and other near-shore sediments transported and deposited by wave action. SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE (v) `Eolian deposits Descriptive of materials transported and deposited by wind. Sediments, generally consisting of medium to fine sand and coarse silt particle sizes, that are well sorted, poorly compacted and may show internal structures such as cross-bedding or ripple laminae, or may be massive. Individual grains may be rounded and show signs of frosting. (vi) Glacial deposits a thick mass of flowing/moving ice, They are generated in areas favored by a climate in which seasonal snow accumulation is greater than seasonal melting i.e (1) polar regions (2) high altitude/mountainous regions (v) TIME Soil formation is a very slow process requiring thousands of years to develop a mature pedon. The period taken by a given soil from the stage of weathered rock (i.e. regolith) up to the stage of maturity is considered as time. The matured soils mean the soils with fully developed horizons (A, B, C). It takes hundreds of years to develop an inch of soil. The time that nature devotes to the formation of soils is termed as Pedologic Time. It has been observed that rocks and minerals disintegrate and/or decompose at different rates; the coarse particles of limestone are more resistant to disintegration than those of sandstone. However, in general, limestone decomposes more readily than sandstone (by chemical weathering). Table 5: Weathering Stage in Soil Formation Stages Characteristic 1 Initial Un weathered parent material 2 Juvenile Weathering started but much of the original material still un weathered 3 Virile Easily weatherable minerals fairly decomposed; clay content increased, slowly weatherable minerals still appreciable 4 Senile Decomposition reaches at a final stage; only most resistant minerals survive 5 Final Soil development completed under prevailing environments SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE 2.3 SOIL FORMING PROCESSES Soil forming processes are determined by climate and organisms (both plants and animals) acting on the local geological surface materials over time under the influence of the slope of the land and human activities. The interaction between these factors initiates a variety of processes. Elementary processes of soil formation (EPP) are the processes that results in the transformation of the mineral mass of soil forming rocks into horizons with differing composition and properties which are typical for various stages of soil formation and reflecting the totality of phenomena governing the evolution of soils. The EPP despite their differences can be divided into four (4) main groups; 1. Accumulation 2. Transfer process in soil (Migration) 3. Transformation 4. losses from the soil Accumulation The main addition into the soil are organic matter from the surface vegetation with the element they contain, addition by rainfall or runoff, e.g. soluble compound and sediments they contain, and addition of particles carried by wind. Transfer process in soil (Migration) Transfer processes involve the vertical and horizontal transport of materials within the soil. These include the following;  Movement of ions and substances by water moving up and down the profile  Transfer effected by microbial action, earthworm and other micro fauna  Transfer effected by cycling of ions by plant Transformation SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE Transformation processes within the soil are; Organic compounds that are formed during inorganic matter decomposition  Organic compounds that are formed during inorganic matter decomposition  Weathering of primary minerals  Formation of secondary minerals losses from the soil Losses from the soil indicate the removal of substances out from the soil surface by erosion and also washing off of soluble materials down into the deeper layers of the soil by leaching All these processes combined together leads to differentiation of soil different horizon. Depending on the complexities of these processes and the restrictiveness of their area of occurrence, these processes can still be classified into simple and complex processes. Simple processes include humification, eluviation, illuviation, leaching, mineralization, amminization, ammonification, nitrification and Denitrification. The processes are noted not only for their simplicity but also for operating in specific part of the soil profile. The complex processes of pedogenesis are combinations of many of the simple processes depending on the prevailing bioclimatic conditions of a particular area, two or more of the simple processes may operate together. Examples of complex processes of pedogenesis are Lateritization, Podzolization, Calcification, Salinization, Gleization and Solonization. 2.3.1 SIMPLE PROCESSES OF PEDOGENESIS humification, mineralization, eluviation, illuviation, leaching, ammonification, nitrification and Denitrification. 1. HUMIFICATION Humification is the process of transformation of raw organic matter into humus. It is extremely a complex process involving various organisms. First, simple compounds such as sugars and SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE starches are attacked followed by proteins and cellulose and finally very resistant compounds, such as tannins, are decomposed and the dark coloured substance, known as humus, is formed. Humification occurs in three phases, namely: 1. rapid initial decomposition of primary plant residues; 2. slow decomposition of plant structural components; 3. alteration of soil organic carbon, Humic Substance genesis. Rapid initial decomposition of primary plant residues The first phase in humification involves the decomposition of labile, plant-derived carbon (litter, or ‘primary resources’). Decomposition of terrestrial plant litter is the mechanism by which carbon and nutrients are returned to either the atmosphere or to a plant available state. Degrading organisms immobilize nutrients such as nitrogen, phosphorus, or calcium in their biomass during this first phase of decomposition. Degradation rate is fast, and bacteria are active at this stage. The utilizable soluble compound at this stage are plant labile C, sugar, amino acids, organic acids. Slow decomposition of plant structural components Degradation rate slows once labile sources of carbon have been utilized, and primarily lignin-encrusted cellulose and hemicelluloses remain. Many fungi and eubacteria, such as actinomycetes, are important during this phase of humification. They are capable of producing a variety of cellulolytic and lignolytic enzymes. Alteration of soil organic carbon, Humic Substance genesis Microbial contribution to this phase is not only through metabolic activity, but also through incorporation of metabolites and biomass components into Humic Substances (HS). Microbial metabolites and cell components can condense abiotically to form Humic Substances (HS). For example, phenolic compounds that are released into the soil from litter or microbial activity are highly reactive and spontaneously undergo nonenzymatic chemical reactions to form more complex molecular structures. Humic Substances (HS) Humified matter represents more than half soil total organic carbon and can be classified in two main types, 1. humic and SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE 2. non-humic substances Humic Substances – These are generally classified into three main groups according to the solubility of each fraction in water adjusted to different acid alkaline (pH levels) conditions: (1) HUMIN, (2) HUMIC ACIDS (HAs), and (3) FULVIC ACIDS (FAs). Non-humic substances – non-humic substances e.g. carbohydrates, proteins, peptides, amino acids, lipids, waxes and organic acids of low molecular weight (1) HUMIN – They are the fraction of humic substances which are not soluble in alkali (high pH) and are not soluble in acid (low pH). Humins are not soluble in water at any pH Humin complexes are considered macro organic (very large) substances because their molecular weights (MW) range from approximately 100,000 to 10,000,000. Functions of Humin 1. improve the soil's water holding capacity, 2. improve soil structure, 3. maintain soil stability, 4. function as an cation exchange system, and generally improve soil fertility. Because of these important functions humin is a key component of fertile soils. 2. HUMIC ACIDS (HAs) --- comprise a mixture of weak aliphatic (carbon chains) and aromatic (carbon rings) organic acids which are not soluble in water under acid conditions but are soluble in water under alkaline conditions. Humic acids consist of that fraction of humic substances that are precipitated from aqueous solution when the pH is decreased below 2. The molecular size of humic acids (HAs) range from approximately 10,000 to 100,000 Functions of Humic Acid 1. Humic acid (HA) polymers readily bind clay minerals to form stable organic clay complexes 2. It readily form salts with inorganic trace mineral elements. SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE 3. These trace elements are bound to humic acid molecules in a form that can be readily utilized by various living organisms. 4. As a result humic acids (HAs) function as important ion exchange and metal complexing (chelating) systems. 3. FULVIC ACIDS (FAs)---They are a mixture of weak aliphatic and aromatic organic acids which are soluble in water at all pH conditions (acidic, neutral and alkaline). Their composition and shape is quite variable. The size of fulvic acids (HFs) are smaller than humic adds (HAs), with molecular weights which range from approximately 1,000 to 10,000. Fulvic acids (FAs) have an oxygen content twice that of humic acids (HAs). They have many carboxyl ( COOH) and hydroxyl ( COH) groups, thus fulvic acids (FAs) are much more chemically reactive. The exchange capacity of fulvic acids (FAs) is more than double that of humic acids (HAs). This high exchange capacity is due to the total number of carboxyl ( COOH) groups present. Functions Because of the relatively small size of fulvic acid (FA) molecules they can readily enter plant roots, stems, and leaves. As they enter these plant parts they carry trace minerals from plant surfaces into plant tissues. Fulvic acids (FAs) are key ingredients of high quality foliar fertilizers. Foliar spray applications containing fulvic acid (FA) mineral chelates Fulvic acids (FAs) are the most effective carbon containing chelating compounds known. They are plant compatible, thus non toxic, when applied at relatively low concentrations. ELUVIATION, It is the mobilization and translocation of certain constituent’s viz. Clay, Fe, humus, CaCO, other salts etc. from one point of soil body to another. Eluviation means washing out. It is the process of removal of constituents in suspension or solution by the percolating water from the upper to lower layers. The eluviation encompasses mobilization and translocation of mobile SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE constituents resulting in textural differences. The horizon formed by the process of eluviation is termed as eluvial horizon (A or E horizon). Translocation depends upon relative mobility of elements and depth of percolation. ILLUVIATION, The process of deposition of soil materials (removed from the eluvial horizon) in the lower layer (or horizon of gains having the property of stabilizing translocated clay materials) is termed as Illuviation. The horizons formed by this process are termed as illuvial horizons (B-horizons, especially Bt) The process leads to textural contrast between E and Bt horizons, and higher fine: total clay ratio in the Bt horizon. LEACHING, Wherever rainfall exceeds evaporation and there is free downward movement of water through the soil pore system, soluble minerals are leached or removed from the soil profile. Continual leaching tends to impoverish the upper mineral horizons by removal of basic cations (cations are ions having a a positive electrical charge e.g. Ca2+. Leaching is most active in sandy soils with high porosity and is least in fine-textured soils such as clays which have restricted pore spaces. MINERALIZATION -- This process of decomposition and liberation of mineral materials from organic material. Aminization and ammonification are performed by heterotrophic microorganisms and nitrification is brought about mainly by autotrophic soil bacteria. Heterotrophs require organic carbon compounds for their energy source. Autotrophic organisms get their energy from the oxidation of organic salts and their carbon from the carbon dioxide in the air. AMINIZATION Simple proteins are hydrolyzed (bonds are broken and water molecules added) to form amines and amino acids. The process can be represented as follows: SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE proteins = R-NH2 + CO2 + energy + other products AMMONIFICATION The amines and amino acids released by aminization are used by other soil heterotrophs and broken down further to ammoniacal compounds. This process, called ammonification, can be represented as follows: R-NH2 + HOH = NH3 + R-OH + energy The ammonia produced by this process may be used in several ways in the soil. 1. Be converted to nitrite and nitrate by the process of nitrification. 2. Be used directly by plants. 3. Be used by soil microorganisms. 4. Be tied up by certain types of soil clays. NITRIFICATION The conversion of ammonium to nitrate is called nitrification. It is an oxidation process and releases energy for the use of soil microorganisms. The conversion is a two step process in which ammonium is first converted to nitrite (NO2) and nitrite is converted to nitrate (NO3). The conversion of ammonium to nitrite is performed by an obligate autotrophic bacterium known as NITROSOMONAS. This process can be represented as follows: 2 NH4+ + 3 O2 = 2 NO2- + 2 H2O + 4 H+ The conversion of nitrite to nitrate is also performed by a number of soil microorganisms but is performed mainly by another group of obligate autotrophic bacteria known as NITROBACTER. This process can be represented as follows: 2 NO2- + O2 = 2 NO3- SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE The resulting NO3- is highly mobile in soils and is easily lost from the soil with water that moves downward laterally through a soil profile. This NO3- is a potential pollutant if it reaches surface and ground water supplies. It is important to remember that these processes require molecular oxygen; that is, they take place most rapidly in well-aerated soils. Poor aeration due to soil wetness or lack of pore space will slow or stop the mineralization process. Also, since living soil microorganisms are responsible for the processes, the rate of reaction is very dependent on soil environmental conditions. These include soil temperature, soil moisture, soil pH, tillage system, cropping system, and the presence of other nutrients. This has practical implications when organic wastes are soil-applied as fertilizers. The rate at which N is released by organic wastes is dependent on the soil environment as well as the characteristics of the waste itself. DENITRIFICATION. Denitrification is the biological reduction of soil nitrates (NO3) under anaerobic conditions. If nitrates are present in the soil and the soil is waterlogged, nitrates can be transformed into N 2 and N2O gases. These gases can then escape to the atmosphere. 2.3.2 SPECIFIC SOIL FORMING PROCESS The basic pedologic processes discuss above provide a framework for later operation of more specific processes such as; Lateritization, Podzolization, Calcification, Salinization, Gleization. 1. Laterization Laterization is a pedogenic process common to soils found in tropical and subtropical environments. High temperatures and heavy precipitation result in the rapid weathering of rocks and minerals, mineralisation of organic matter is complete and rapid. Movements of large amounts of water through the soil cause eluviations and leaching to occur. Almost all of the by products of weathering, very simple small compounds or nutrient ions, are translocated out of the soil profile by leaching if not taken up by plants for nutrition. The two exceptions to this process are iron and aluminum compounds. Desilication (the removal of combined silica in preference to the Fe and Al which generally accumulate and oxidize to sesquoxide (trivalent SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE oxides)) occurs. Iron oxides give tropical soils their unique reddish coloring. Heavy leaching also causes these soils to have an acidic pH because of the net loss of base cation. Depending on the water situation, the process of lateritization may produce stratified or unstratified soil profile, in the former case, a marked or fluctuating water facilitates the formation of an indurated (hard) zone above the water table. A mottled zone in the area of fluctuation and a pallied zone under the water table or zone of complete or permanent saturation. SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE 2. Podzolization Podzolization is associated with humid cold mid-latitude climates and coniferous vegetation. Decomposition of coniferous litter and heavy summer precipitation create a soil solution that is strongly acidic. This acidic soil solution enhances the processes of eluviation and leaching causing the removal of soluble base cations and aluminum and iron compounds from the A horizon. This process creates a sub-layer in the A horizon that is white to gray in color and composed of silica sand. SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE Podzols (from the Russian, pod, meaning under, and zola, meaning ash) SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE 3. Calcification Calcification occurs when evapotranspiration exceeds precipitation causing the upward movement of dissolved alkaline salts from the groundwater. At the same time, the movement of rain water causes a downward movement of the salts. The net result is the deposition of the translocated cations in the B horizon. In some cases, these deposits can form a hard layer called caliche. The most common substance involved in this process is calcium carbonate. Calcification is common in the prairie grasslands. SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE 4. Salinization Salinization is a process that functions in the similar way to calcification. It differs from calcification in that the salt deposits occur at or very near the soil surface. Salinization also takes place in much drier climates. Saline soil occur where saline groundwater comes near to the surface or where the evapo- transpiration is considerably higher than precipitation, at least during a large part of the year. Salts dissolved in the soil moisture remain behind after evaporation of the water and accumulate at or near the surface. Their morphology, characteristics and limitations to plant growth depend on the amount, depth and composition of the salts. SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE SOLONCHAKS: Strongly saline soil (from the Russian, sol, meaning salt and chak, meaning salty area). 5. Gleization Gleization is a pedogenic process associated with poor drainage. This process involves the accumulations of organic matter in the upper layers of the soil. In lower horizons, mineral layers are stained blue-gray because of the chemical reduction of iron. iron can be present in bivalent (Fe2+, the ferrous ion) and in trivalent forms (Fe3+, the ferric ion respectively). SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE Fe2+, the ferrous ion Fe3+, the ferric ion (commonly called rust The ferrous form is soluble, whereas the ferric form is not. The more oxidized the soil becomes, the more the ferric forms dominate SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE 2.4 SOIL PROFILE The vertical cross section of the soil is called the soil profile. It is seldom uniform in depth, and typically consists of a succession of more-or-less distinct layers or strata. Such layers results from the pattern of deposition, or sedimentation, as can be observed in wind-deposit (aeolian) soils and particularly in water deposit (alluvial) soils. If however the layers form in place by internal soil forming (pedogenic) processes, they are called horizons. 2.4.1 Master Horizon and its Designation The top layer, A horizon, is the zone of major biological activity and is therefore generally enriched with organic matter and often darker in colour than the underlying soil. The B horizon SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE is where some of the materials migrating from the A horizon (such as clay or carbonates) tends to accumulate. Under the B horizon lays the C horizon, which is the soil parent material. In the case of a residual soil formed in place from the bedrock, the C horizon consists of the weathered and fragmented rock material. In other case, the C horizon consists of alluvial, Aeolian or glacial sediment. The A, B, C sequence of horizons is clearly recognizable in some cases as for example in a typical zonal soil such as podsol. In other cases, no clearly discernable B horizon may be discernible, the soil is then characterised by A,C profile, in still some other cases, as in some very recent alluvium, hardly any profile differentiation is apparent. The character of the profile depends primarily on the climate, and secondarily on the parent materials, the vegetation, the topography and time. SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE Master Horizon Designation 01 – Undecomposed litter 02 – Partly decomposed litter A1 – Zone of humus accumulation A2 (E)– Zone of strongest leaching (eluviation), also called albic horizon A3 – Transitional to B horizon, has properties more like A than B B1 – Transitional, more like B than A horizon (sometime absent) B2 -- Zone of maximum accumulation of clay particles, Fe and Al oxides and humus (illuviation). It is referred to as argillic horizons SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE B3 – Transitional to C horizon C – Unconsolidated rock R – Consolidaterd rock An important aspect of soil formation and profile development are the twin processes of eluviation and illuviation, wherein clay and other substances emigrate from the overlying eluvial A horizon and accumulate the underlying illuvial B horizon. In arid regions, salts such as calcium sulphate and calcium carbonate dissolved from upper part of the soil, may precipitate at some at some depth to form a cemented pan. 2.4.2 Suffixes to the Master Horizon Symbols Lower case letters can be added as suffixes to the master horizon symbols. Some of the symbols and what they stand for are as follows a – highly decomposed e – OM of intermediate decomposition g – Shinning gleying, evident by mottled appearance of the horizon due to the precipitation of Fe compounds. It is an indication of poor drainage. h – illuvial accumulation of humus i – slightly decomposed organic matter k – accumulation of carbonates m – strong cementation p – Plow larger or a mechanically disturbed zone q – accumulation of silica s – illuvial accumulation of sesquoxide t – illuvial accumulation of clay i.e argillic y – accumulation of gypsum SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE 3.0 SOIL PHYSICAL PROPERTIES Soil is a heterogeneous, polyphasic, particulate, dispersed and porous system. The three phases of ordinary nature are represented in the soil as follows; 1. The solid phase which constitute the soil matrix 2. The liquid phase consists of soil water, which always contain dissolved substances so that it should properly be called the soil solution; and 3. The gaseous phase, the soil atmosphere. The solid matrix of the soil includes particles which vary in chemical and mineralogical composition as well as size, shape, and orientation. It also contains amorphous substances, particularly organic matter which is attached to the mineral grains and often binds them together to form aggregates. The organisation of the solid components of the soil determines the geometric characteristics of the pore spaces in which water and air are transmitted and retained. Soil air and water vary in composition, both in time and space. The relative proportion of the three phases in soil varies continuously, and depends upon such variables as weather, vegetation and management 3.1 SOIL TEXTURE This is a stable and an easily determined soil characteristic and refers to the size range of particles in the soil and carries both qualitative and quantitative connotations. Qualitatively it SCHOOL OF AGRICULTURE AND AGRICULTURAL TECHNOLOGY (SAAT) CSP202 (BASIC SOIL SCIENCE) CROP, SOIL AND PEST MANAGEMENT DEPARTMENT, FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE represents the ‘feel’ of the soil materials, whether coarse and gritty or fine and smooth. Quantitatively it denotes the measured distribution of particles sizes or the proportion of the various sizes range of particles which occur in a given soil. It is therefore estimated by feeling and manipulating a moist sample, or more accurately by laboratory analysis By feel, Soil texture depends on the amount of each size of particle in the soil. Sand, silt and clay are names that describe the size of individual particles in the soil. Sand are the largest particles and they feel "gritty." Silt are medium sized, and they feel soft, silky or "floury." Clay is the smallest sized particles, and they feel "sticky" and they are hard to squeeze. It is more or less conventional to define soil materials as particles smaller than 2 mm in diameter. Larger particles are generally referred to as gravel, and still larger rock fragments, several centimeters in diameters are variously called stones, cobbles, or if very large, boulders. Soil particle sizes are traditionally characterised into three different conveniently separable size range known as textural fractions or separates namely; Sand (2 to 0.05 mm) USDA, Sand (2 to 0.02 mm) ISSS, Silt (0.05 to 0.002 mm) and Clay (