Soil Functions and Formation PDF

CHAPTER ONE: TUE SOIL AROUND US: 1.1 FUNCTIONS OF SOILS IN OUR ECOSYSTEM: Literature source: Title: The Nature and Properties of Soils, I led Nyle C.Brady & Raymond R. Weil. Page Reference: _pgs In any ecosystetn, whether you...

CHAPTER ONE: TUE SOIL AROUND US: 1.1 FUNCTIONS OF SOILS IN OUR ECOSYSTEM: Literature source: Title: The Nature and Properties of Soils, I led Nyle C.Brady & Raymond R. Weil. Page Reference: _pgs In any ecosystetn, whether your backyard, a farm yard, a forest, or your garden bed, soils have five key roles to play (Figure 1.3): 1.1.1 First. soils support the growth of higher plants mainly by providing a medium for plant roots and supplying nutrient elements that are essential to the entire plant. Properties of the soil often determine the nature of the vegetation present and, indirectly, and number and types of animals (including people) that the vegetation can support. 1.1.2 Second, soils properties are the principal factor controlling the fate of water in the hydrologic system. Water loss, utilization, contamination, and purification are all affected by the soil. 1.1.3 Third, the soil functions as nature's recycling system. Within the soil, waste products and dead bodies of plants, animals, and people are assimilated (absorbed into the plant). 1.1.4 Fourth, soils provide habitats for a myriad of living organisms, from small manunalsand reptiles to tiny insects to microscopiccells of unimaginable numbers and diversity. 1.1.5 Finally, in human-builtecosystems,soils plays an importantrole as an engineeringmedium. Soil is not only an important building material in the form of earth fill and bricks (baked soil material), but provides the foundation for virtually every road, airport. and house we build.  1.2 Medium For Plant Growth: ' ' What " things do plants obtainfrom the soils in which their roots proliferate? Plant roots depend on soils for the following re»sons: 1.2.I Plant roots depend on the process respiration to obtain energy. Since root Of important respiration, produces carbon dioxide (C02) and uses oxygen (02), an function of the soil is "ventilation" —allowing C02 to escape and fresh 02 to enter the root zone. This ventilationis accomplishedvia the net work of soil pore spaces. The spaces between each soil pore will determine the concentration (build-up) of any toxic gases in the soil. 1.2.2 Soil absorb rainwater, and hold it where it can be used by plants roots. While the leaves are exposed to sunlight, the plant requires a continuos stream of water to use in cooling, nutrient transport, turgor manitenance, and photosynthesis. The water-holding capacity is therefore essential for plants survival. 1.2.3 As soils moderatesmoisture levels in the root environment, soils also moderates temperature fluctuations. The insulating properties of soils protect the deeper portions of the root systems from the extremes of hot and cold that often occur at the soil surface. 1.2.4 A fundamentalrole of soils is to provide inorganicmineral nutrients such as nitrogen, sulphur and potassium as plant foods for plant growth. These minerals are supplied by the soil in a dissolved form to the plants 1.2.5 It is clear from our discussion that the soil mass provides physical support, anchoring the root system so that the plant does not fall over. Occasionally plants will fall over during windy conditions if the shallow soils or restrictive layers make the top-heavy. It is true that plants can be grown in nutrient solutions without soil (hydroponics), but then the plant-support functions of soils must be engineered into the system and maintained at a high cost of time, effort, and management.Although hydroponic production can be feasible on a small scale for a few high-valued plants, the production of the worlds food and fibre and the maintenanceof natural ecosystems will always depend on the use of millions of square kilometers of productive soils.  CHAPTER 2 FORMATION GENESIS) OF SOILS FROM PARENT MATERIALS: Literature source: Title: The Nature and Properties of Soils, 1led Authors: Nyle C.Brady & Raymond R. Weil. Page Reference: pg25 - pg52 2.1 Five maior factors control the formation of soils: 2.1.1 Parent materials (geological or organic addition to the soil) 2.1.2 Climate (primarily precipitation & temperature) 2.1.3 Biota (living orgainisms,especiallynative vegetation, microbes, soil animals, and human beings) 2.1.4 Topography (configuration of the soil surface) 2.1.5 Time the parent materials are subjected to soil formation. 2.2.1 Parent Material: Geological processeshave brought to the earth's surface numerous parent materilas in which soils have formed. As the upper layers of rock are exposed they are subjectedto weathering.The weathered rock give rise to various soils, which consist of varying textures. Organic Deposits: The organic material accumulates in wet places where plant growth exceeds the rate of residue decomposition. For centuries, residues accumulated from water-loving plants such as pondweeds, cattails, sedges, reeds, mosses, shrubs, and certain trees. These residues sank into the water, where their oxidation was curtailed. As a result, organic deposits of up to several meters in depth are common. Collectively these organic deposits are called peat.  of peat are Based on the nature of the parent materials, four kinds recognized: (fig 2.19) Moss peat, the remains of mosses such as sphagnum. as Telmatic or herbaceous peat, residues of herbaceous plants such sedges, reeds, and cattails. Terresticor woodypeat, from the remains of woody plants, including trees and shrubs. Limnic or sedimentarypeat, remains of aquatic plants (e.g., algae) and of fecal material of aquatic animals. 2.1.2 Climate: It is the most influential of the four factors acting on parent material because it determines the nature of the weathering that occurs. Temperature and precipitation affect the rates of chemical, physical, and biological processes responsible for profile development. For every 10 degrees celcius rise in temperature the rates of biological chemical reaction doubles. Soil organisms are sensitive to temperature and moisture. Temperature and moisture relations influence the organic matter content in the soil. Climate also influences the natural vegetation. In humid regions plentiful rainfall provides an environment favourable for growth of trees. In contrast, grasslands are the dominant native vegetation in semiarid regions, and shrubs and brush of various kinds dominate in arid areas. 2.2.3 Biota: Living Organisms: (fig 2.23 & 2.24) Soil organismplay a major role in profile differentiation.Their actions are responsible for the following: Organic matter accumulation. Profile mixing. Nutrient cycling. Structural stability. Higher organic content gives the soil the following characteristic: Darker colour. Higher moisture. Higher cation exchange capacity (CEC). Other effects: Coniferous trees (eg. Pines, firs) arc low in metallic cations (calcium, magnesium, potassium) and encourages acid JcvcJs in soils. The recycling of plant litter falling from trees is low in cvcrgrccnscompared to deciduous trees. The removal of base-formingcations by leachingunder coniferoustrees is rapid. Azotobacter —bacteria that can fix atmospheric nitrogen into usable componds for plant growth. Earthworms and burrowing organism aerate and stir the soil thereby increasing soil stability and water infiltration. Ants anf termites build mounds and transports soil from one horizon to another. 2.2.4 Topography: It can hasten or delay the work of climatic forces. In smooth, flat country, excess water is removed less rapidly than in rolling areas. Rolling to hilly topography encouragesnatural erosion of the surface layers, which reduces the possibility of deep soil. On the other hand if water stands for part or the entire year, the climate is less effective in regulating soil development. 2.2.5 Time: The length of time that materials are subjected to weathering influences soil formation. The time required for the development of a horizon will be influenced by the parent material, climate and vegetation.  2.3 THE SOIL PROFILE: Literature source: Title: The Nature and Properties of Soils, I led Authors: Nyle C.Brady & Raymond R. Weil. Page Reference: pg52 - pg53 Introduction: The layering or hofizon development described in the previous section gradually gives rise to natural bodies called soils. Each soil is characterizedby a given sequenceof these horizons. A vertical exposure of this sequenceis termed a soil profile. Attentionwill now be given to the major horizons making up soil profile and the terminology used to describe them. (fig 2.26) 2.3.1 The Master Horizons and layers: Five master horizons are recognized and are designatedusing the capital letters O, A, E, B, and C. 2.3.1.1 O Horizon (organic): The O group is comprised of organic horizons that form above the mineral soil. They result from litter derived from dead plants and animals. O horizons usually occur in forested areas and generallyabsent in grassland regions. The specific horizons are: Oi Organic horizons of the original plant and animal residues, only slightly decomposed (fibric). Oe Organic horizon, residues intermediately decomposed (hemic). Oa Organic horizons, residues highly decomposed (sapric). 2.3.1.2 A Horizons: These are the top most mineral horizons. They generallycontain enough partially decomposed (humified) organic matter to darken the soil colour more than that of the lower horizons.A horizonsare often coarser in texture, having lost some of the finer materials to the lower horizons. The A horizon is sometimes referred to the topsoil.  2.3.1.3 E Ilorizons: These are zones of tna.\ltnutll leaching or eluviation (lion) laitn oc c. out, and lavere, to wash)jots clay, iron, and alutnttutltn oxides, which leaves-a concentration of resistant tninerals, such as in the sand and sill sizes. horizon is generally lighter in colour than the A horizon and is Il)tjnd underneath theg\ horizon. 2.3.1.4 B Horizon (Illuvial): These are subsurface hortzons in the accutnulation of tuaterials by illuviation (from Latin il, in, and laverc', to wash) has taken place, In humid regions the B horizons are the layers of acctltnulation of materials such as iron and alutlltnitltn oxides and silicate clays, sotne of which may have been formed in place. In arid & semiarid regions, calcium carbonate, calctutn sulphate, and other salts may accumulate in the B horizon. The B horizons are sometimes refer-redto as the subsoil. 2.3.1.5 C Horizon: The C horizon is unconsolidated material underlying the solutn (A & B horizons). The C horizons is outside the zones of tuajor biological activities and is generally little affected by the process that fortned the horizons above it. Its upper layers may in time to become a part of the solum as weathering and erosion continue. 2.3.1.6 These are underlying consolidated rock, with little evidence of weathering. 2.3.1.7 Transitional Horizons: These horizons are transitional between the tuaster horizons and C). They may be dominated by properties of one horizon but have protuinent characteristics of another. The two applicable capital letters are used to designate the transition horizons (e.g., AE, IEB, BE, and BC). The dotninant horizon being listed before the subordinate.  2.3.1.8 Regolith: Literature source: Title: The Nature and Properties of Soils, 1led Authors: Nyle C.Brady & Raymond R. Weil. Page Reference: pg9 —pg13 It is the unconsolidated debris found above the bedrock (R horizon). May be shallow or hundreds of feet deep. It may be material that has weathered from the underlying rock or it may have been transportedby the action of wind, water, or ice and deposited upon the bedrock.Thus all or part of the regolithmay or may not be related to the rock now found below it. The upper part of the regolith, usually the upper 1 to 2 meters, has been affected by the activitiesof living organisms,and is different from the deeper layers. Can often been seen in road cuts and other excavations. (fig 1.9) 2.3.1 Topsoil & Subsoils: Literature source: Title: The Nature and Properties of Soils, 1led Authors: Nyle C.Brady & Raymond R. Weil. Page Reference: pg12 —pg13 2.3.2.1 Topsoils (Horizons Oi —A): Organically enriched layers. The upper 12 to 25 centimetersof soil is modified when plowed and cultivated, therefore also referred as the plow layer. In cultivated soils the majority of plant roots are found in the topsoil. It contains a large part of nutrients and water needed by plants. The chemical properties of the topsoil may be easily altered by mixing in organic and inorganic amendments. The physical structure of the topsoil, especially the part nearest the surface is readily affected by management operations such as tillage and the application of organic materials. A loose (not being compacted)topsoil structureis importantto avoid excessive water runoff, and to encourage air & water movement into the  soil. It will also facilitate for removal of toxic gases out of the soil environment. The use of topsoil is common to provide a rooting medium suitable for lawns, groundcovers, annuals, perennials and shrubs, and fine grading of the landscape for sport field construction. 2.3.2.2 Subsoil (Horizons E —C): It is the soil layers that underlie the topsoil. Not normally seen from the surface and is usually below the depth of tillage. Much of the water needed by plants is stored in the subsoil. Supplies important quantities of certain plant nutrients (foods) required by plants. In certain soils the upper parts of the subsoilmay be the similar to the lower parts of the topsoils Impermeable subsoil layers can impede root penetration, as can very acid subsoils. Poor drainage in subsoils can result in waterlogged conditions in the topsoil. Good fertilization of the topsoil can produce vigorous plants whose roots are capable of greater exploration in subsoil layers. for the planting of large landscape trees, rough grading of the landscape, construction of sport fields, building of greenhouses, potting sheds, Conservatories, and roadways