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soil

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soil

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  1. soil • Is defined as the top layer of the earth’s crust. • It is formed by mineral particles, organic matter, water, air and living organisms. It is in fact an extremely complex, variable and living medium.

  2. The interface between the earth, the air and the water, soil is a non-renewable resource which performs many vital functions: food and other biomass production, storage, filtration and transformation of many substances including water, carbon, nitrogen.  • Soil has a role as a habitat and gene pool, serves as a platform for human activities, landscape and heritage and acts as a provider of raw materials. • These functions are worthy of protection because of their socio-economic as well as environmental importance.

  3. Different Types of Soil • Sandy • Clay • Peat • Loam • Silt

  4. Sandy • Sand is a unique soil type in that it is composed of very large particles. • When comparing this type of soil to different soil types it is obvious that sand cannot carry water efficiently because of the spaces between these particles.

  5. Plants that are unlucky enough to be planted in sandy soil don’t quite receive the same amount of nutrients as the plants that are planted in other soil types such as loam. This prevents the seedlings or the plants from completely extracting everything it needs from the soil or the water. This is because the water that is poured over sandy soil will just pass through. This runoff of water will take the nutrients and the water with it.

  6. Sand could be thought of as a very fine mixture of gravel. Sand itself is composed of very fine limestone, granite and other rock types. Because of this composition, the use of sand extends to the building construction. Sand is a major component in concrete when it is mixed in with the cement. Other uses of sand involve glass and silicon chip manufacturing.

  7. Silty soil is much smoother than sandy soil because of its smaller particles. When silty soil is rolled between one’s finger it will leave behind dirt. When it is wet it will create a slippery surface. Silt, unlike sand, drains water poorly as it tends to retain moisture.

  8. Siltysoil is also considered to be similar to sand because of its composition. It is also composed of crystals and granules but the difference is with their drainage and their nutrients. Because it drains much slower than sand it could retain nutrients more efficiently. Using a lot of silt in the garden will require a lot of maintenance as this soil type will tend to compact easily. This will prevent proper aeration which will be harmful to one’s plants. This makes it ideal to use in gardens and other planting needs. It allows water to drain slower than sand does but it pales in comparison to clay in this regard.

  9. Clay • Clay just like sand, is formed from the gradual weathering of rocks. Clay is usually found in places that are downstream or below large formations of rocks because of the weathering. • In nature, clay is distinguished from other types of granular soil by its particle size. Though there are instances and there are locations where clay and silt are mixed in together.

  10. Loam Loam is an all time gardeners’ favourite. This type of soil is a mixture of sand, silt and clay. This means that it contains the best of each of these different soil types. This makes it ideal to be the base of seedlings and plants.

  11. The most fertile farm lands all over the world naturally contain a lot of loam for planting purposes. The agricultural industry owes a lot of its success to the use of loam. This is why loam is a favorite among farmers and gardeners alike. Loam is perfect for gardening and tree planting purposes as it is able to retain moisture enough for the nutrients to be extracted by the roots and it is able to provide proper drainage enough to prevent root rot. This is why those who are about to enter the world of planting and gardening would be right in picking loam as their base soil

  12. Peat • Peat is a unique type of soil in that one of its main uses is realized after it is burned. It is actually used as fuel in some parts of the world including Ireland and Finland. • Peat is usually found in areas near bogs and other marsh lands where trees are scarce. They are composed of some granular material that may be similar in size to the granules of sand and clay. These granules are typically composed of quartz and feldspar. • The physical characteristics of peat make it unfavourable for planting and gardening purposes. The consistency of peat makes it easy to be compressed. If there is enough pressure, the water that is suspended in peat can be forced out. This is why it is not really an ideal type of soil for planting as nutrients and moisture could easily escape.

  13. When peat is dried it could now fulfil one of its main functions. This is to be made into fuel. In areas where trees are scarce, peat is used in cooking and other forms of heating instead of firewood. • These are the different basic soil types that are found on earth. These different types of soil each have very different uses. This makes it necessary for anyone who wants to enter agriculture or gardening to really know which soil types are best for the different required reasons.

  14. The soil formation • The formation of soil happens over a very long period of time. It can take 1000 years or more. Soil is formed from the weathering of rocks and minerals. • The surface rocks break down into smaller pieces through a process of weathering and is then mixed with moss and organic matter.

  15. Over time this creates a thin layer of soil. Plants help the development of the soil. How? The plants attract animals, and when the animals die, their bodies decay. Decaying matter makes the soil thick and rich. This continues until the soil is fully formed. The soil then supports many different plants.

  16. Weathering Weathering is the process of the breaking down rocks. There are two different types of weathering. Physical weathering and chemical weathering. In physical weathering it breaks down the rocks, but what it's made of stays the same. In chemical weathering it still breaks down the rocks, but it may change what it's made of. For instance, a hard material may change to a soft material after chemical weathering.

  17. Soil Profile

  18. Soil Profile refers to the layers of soil; horizon A, B, and C. If you're wondering what horizon A is, here's your answer: horizon A refers to the upper layer of soil, nearest the surface. • It is commonly known as topsoil. In the woods or other areas that have not been plowed or tilled, this layer would probably include organic litter, such as fallen leaves and twigs . • The litter helps prevent erosion, holds moisture, and decays to form a very rich soil known as humus. Horizon A provides plants with nutrients they need for a great life.

  19. The layer below horizon A, of course, has to be horizon B. Litter is not present in horizon B and therefore there is much less humus. Horizon B does contain some elements from horizon A because of the process of leaching. Leaching resembles what happens in a coffee pot as the water drips through the coffee grounds. Leaching may also bring some minerals from horizon B down to horizon C. • If horizon B is below horizon A, then horizon C must be below horizon B. Horizon C consists mostly of weatherized big rocks. This solid rock, as you discovered in Soil Formation, gave rise to the horizons above it. • Soil profiles look different in different areas of the world. They are affected by climate and other things.

  20. temperate desert prairie

  21. Soil formation begins first with the break down of rock into regolith. Continued weathering and soil horizon development process leads to the development of a soil profile, the vertical display of soil horizons.

  22. A Typical Soil Profile (after Oberlander & Muller, 1987) O Horizon At the top of the profile is the O horizon. The O horizon is primarily composed of organic matter. Fresh litter is found at the surface, while at depth all signs of vegetation structure has been destroyed by decomposition. The decomposed organic matter, or humus, enriches the soil with nutrients (nitrogen, potassium, etc.), aids soil structure (acts to bind particles), and enhances soil moisture retention.

  23. A Horizon Beneath the O horizon is the A horizon. The A horizon marks the beginning of the true mineral soil. In this horizon organic material mixes with inorganic products of weathering. The A horizon typically is dark colored horizon due to the presence organic matter. Eluviation, the removal of inorganic and organic substances from a horizon by leaching occurs in the A horizon. Eluviation is driven by the downward movement of soil water. E Horizon The E horizon generally is a light-colored horizon with eluviation being the dominant process. Leaching, or the removal of clay particles, organic matter, and/or oxides of iron and aluminum is active in this horizon. Under coniferous forests, the E horizon often has a high concentration of quartz giving the horizon an ashy-gray appearance.

  24. B Horizon Beneath the E horizon lies the B horizon. The B horizon is a zone of illuviation where downward moving, especially fine material, is accumulated. The accumulation of fine material leads to the creation of a dense layer in the soil. In some soils the B horizon is enriched with calcium carbonate in the form of nodules or as a layer. This occurs when the carbonate precipitates out of downward moving soil water or from capillary action.

  25. The diagram below illustrates the effect of climate on eluviation and illuviation. Eluviation is significant in humid climates where ample precipitation exists and a surplus in the water balance occurs. Illuvial layers are found low in the soil profile. Illuvial zones are found closer to the surface in semiarid and arid climates where precipitation is scarce. Capillary action brings cations like calcium and sodium dissolved in soil water upwards where they precipitate from the water.

  26. Figure 11.8 Eluviation and illuviation under humid, semiarid and arid conditions. (after Marsh, 1987)

  27. C Horizon The C horizon represents the soil parent material, either created in situ or transported into its present location. Beneath the C horizon lies bedrock. Figure 11.9Glacial till exposed in a moraine; a typical parent material for soils in the central United States.(Image Source: Agriculture Agri-Food Canada. Used with permission)

  28. The preceding paragraphs describe a generic soil profile, yet not all soils have each one of the horizons, nor are they all the same with respect to thickness composition and structure. Newly formed "immature" soils may only have an O-A-C sequence while older more "mature" soils display the full profile of horizons as described above. The particular compositional, structural and chemical composition of the soil depends on the various factors that influence soil formation.

  29. Soil typically consists of layers of material, called horizons, which differ in both texture and appearance. A soil profile is a cross section of these layers, and it measures the different characteristics of each layer. Although every soil from around the world has a different soil profile, most soils consist of three or more layers, including the topsoil, subsoil, and bedrock. The top layer is generally finer and contains less rocks than the deeper layers.

  30. Topsoil is the uppermost part of a soil profile, and it is the ground on which people and animals walk. Plants will also typically lay the majority of their roots in the topsoil. It can be as thin as two inches (5.1 cm) or as thick as 5 feet (1.5 m), and it is often a dark color, sometimes even black. In uncultivated areas, it may be littered with such organic matter as leaves, twigs, or dead animals that serve to help prevent erosion, hold moisture, and produce nutrient-rich soil. When organic matter decays, it is often referred to as humus, and it contains vital nutrients. It is this layer of the soil profile from which plants get most of their nutrients.

  31. The subsoil is the layer of the soil profile that lies directly beneath the topsoil. There is usually no litter or debris present in this soil layer, and it is often lighter in colour. Subsoil often consists of clay, silt, pebbles, and sand, depending on the area, and it generally contains an abundance of minerals that have leached down from the upper layers of the soil. As a person digs deeper and deeper into the soil, he will find that it gets rockier and rockier. Some scientists consider the next layer of the soil profile, called the regolith, to be part of the subsoil, while others consider it to be a completely separate layer.

  32. This layer almost never contains plant roots or other organic matter, but is made up primarily of soil and small, weathered rocks. The bedrock layer is present in just about every different type of soil profile. This layer is made of hard, solid rock, which is eroded and weathered to produce most of the soil above it. Bedrock can be as little as 5 feet (1.5 m) below the surface, or it can even be exposed in some areas. In situations where much of the upper soil has been deposited from somewhere else, however, the bedrock can lay hundreds of feet beneath the surface.

  33. Soil erosion Soil erosion is one form of soil degradation along with soil compaction, low organic matter, loss of soil structure, poor internal drainage, salinisation, and soil acidity problems. These other forms of soil degradation, serious in themselves, usually contribute to accelerated soil erosion.

  34. Soil erosion is a naturally occurring process on all land. The agents of soil erosion are water and wind, Soil erosion may be a slow process that continues relatively unnoticed, or it may occur at an alarming rate causing serious loss of topsoil. The loss of soil from farmland may be reflected in reduced crop production potential, lower surface water quality and damaged drainage networks.

  35. Erosion by Water The rate and magnitude of soil erosion by water is controlled by the following factors:

  36. Rainfall Intensity and Runoff Both rainfall and runoff factors must be considered in assessing a water erosion problem. The impact of raindrops on the soil surface can break down soil aggregates and disperse the aggregate material. Lighter aggregate materials such as very fine sand, silt, clay and organic matter can be easily removed by the raindrop splash and runoff water; greater raindrop energy or runoff amounts might be required to move the larger sand and gravel particles.

  37. Soil Erodibility Soil erodibility is an estimate of the ability of soils to resist erosion, based on the physical characteristics of each soil. Generally, soils with faster infiltration rates, higher levels of organic matter and improved soil structure have a greater resistance to erosion. Sand, sandy loam and loam textured soils tend to be less erodible than silt, very fine sand, and certain clay textured soils.

  38. Slope Gradient and Length Naturally, the steeper the slope of a field, the greater the amount of soil loss from erosion by water. Soil erosion by water also increases as the slope length increases due to the greater accumulation of runoff. Consolidation of small fields into larger ones often results in longer slope lengths with increased erosion potential, due to increased velocity of water which permits a greater degree of scouring (carrying capacity for sediment).

  39. Vegetation Soil erosion potential is increased if the soil has no or very little vegetative cover of plants and/or crop residues. Plant and residue cover protects the soil from raindrop impact and splash, tends to slow down the movement of surface runoff and allows excess surface water to infiltrate.

  40. The erosion-reducing effectiveness of plant and/or residue covers depends on the type, extent and quantity of cover. Vegetation and residue combinations that completely cover the soil, and which intercept all falling raindrops at and close to the surface and the most efficient in controlling soil (e.g. forests, permanent grasses ). Partially incorporated residues and residual roots are also important as these provide channels that allow surface water to move into the soil.

  41. Conservation Measures Certain conservation measures can reduce soil erosion by both water and wind. Tillage and cropping practices, as well a land management practices, directly affect the overall soil erosion problem and solutions on a farm. Certain conservation measures can reduce soil erosion by both water and wind. Tillage and cropping practices, as well a land management practices, directly affect the overall soil erosion problem and solutions on a farm. When crop rotations or changing tillage practices are not enough to control erosion on a field, a combination of approaches or more extreme measures might be necessary. For example, contour plowing, strip cropping, or terracing may be considered. When crop rotations or changing tillage practices are not enough to control erosion on a field, a combination of approaches or more extreme measures might be necessary. For example, contour plowing, strip cropping, or terracing may be considered.

  42. Effects Sheet and Rill Erosion Sheet erosion is soil movement from raindrop splash resulting in the breakdown of soil surface structure and surface runoff; it occurs rather uniformly over the slope and may go unnoticed until most of the productive topsoil has been lost. Rill erosion results when surface runoff concentrates forming small yet well-defined channels (Figure 1). These channels are called rills when they are small enough to not interfere with field machinery operations. The same eroded channels are known as gullies when they become a nuisance factor in normal tillage. Figure 1. Both sheet and rill erosion are occurring on this field.

  43. Gully Erosion There are farms in Ontario that are losing large quantities of topsoil and subsoil each year due to fully erosion (Figure 2). Surface runoff, causing gull formation or the enlarging of existing gullies, is usually the result of improper outlet design for local surface and subsurface drainage systems. The soil instability of fully banks, usually associated with seepage of ground water, leads to sloughing and slumping (caving-in) of bank slopes. Such failures usually occur during spring months when the soil water conditions are most conducive to the problem. Figure 2. Gullying like this can be stopped by employing proper control measures.

  44. Gully formations can be difficult to control if remedial measures are not designed and properly constructed. Control measures have to consider the cause of the increased flow of water across the landscape. This where the multitude of conservation measures come into play. Operations with farm machinery adjacent to gullies can be quite hazardous when cropping or attempting to reclaim lost land.

  45. Stream and Ditch Bank Erosion Poor construction, or inadequate maintenance, of surface drainage systems, uncontrolled livestock access, and cropping too close to both stream banks has led to bank erosion problems. Figure 3. Reshaping and vegetating this ditch bank would stabilize this soil erosion problem.

  46. The direct damages from bank erosion include: • The loss of productive farmland. • The undermining of structures such as bridges. • The washing out of lanes, roads and fence rows. • Poorly constructed tile outlets may also contribute to stream and ditch bank erosion. Some do not function properly because they have no rigid outlet pipe, or have outlet pipes that have been damaged by erosion, machinery, inadequate or no splash pads, and bank cave-ins.

  47. Erosion by Wind The rate and magnitude of soil erosion by wind is controlled by the following factors:

  48. Erodibility of Soil Very fine particles can be suspended by the wind and then transported great distances. Fine and medium size particles can be lifted and deposited, while coarse particles can be blown along the surface (commonly known as the saltation effect). The abrasion that results can reduce soil particle size and further increase the soil erodibility. Soil Surface Roughness Soil surfaces that are not rough or ridged offer little resistance to the wind. However, over time, ridges can be filled in and the roughness broken down by abrasion to produce a smoother surface susceptible to the wind. Excess tillage can contribute to soil structure breakdown and increased erosion.