Unit 3

• Soil is our life support system. Soils provide anchorage for roots, hold water and nutrients. Soils are home to myriad micro-organisms that fix nitrogen and decompose organic matter, and armies of microscopic animals as well as earthworms and termites. We build on soil as well as with it and in it.
• Soil plays a vital role in the Earth's ecosystem. Without soil human life would be very difficult. Soil provides plants with foothold for their roots and holds the necessary nutrients for plants to grow; it filters the rainwater and regulates the discharge of excess rainwater, preventing flooding; it is capable of storing large amounts of organic carbon; it buffers against pollutants, thus protecting groundwater quality; it provides Man with some essential construction and manufacturing materials, we build our houses with bricks made from clay, we drink coffee from a cup that is essentially backed soil (clay); it also presents a record of past environmental conditions.
• Soil functions


  • Food and other biomass production
  • Environmental Interaction: storage, filtering, and transformation
  • Biological habitat and gene pool
  • Source of raw materials
  • Physical and cultural heritage
  • Platform for man-made structures: buildings, highways
• Soil


  The unconsolidated mineral or organic material on the immediate surface of the earth that serves as a natural medium for the growth of land plants
• Soil


  The unconsolidated mineral or organic matter on the surface of the earth that has been subjected to and shows effects of genetic and environmental factors of: climate (including water and temperature effects), and macro- and microorganisms, conditioned by relief, acting on parent material over a period of time
• Soil chemistry


  Discipline embracing all chemical and mineralogical compounds and reactions occurring in soils and soil-forming processes
• Pedology


  Scientific discipline concerned with all aspects of soils, including their physical and chemical properties, the role of organisms in soil production and in relation to soil character, the description and mapping of soil units, and the origin and formation of soils
• Dirt


  Soil that is out of place in our world – whether tracked inside by shoes or on our clothes. Dirt is also soil that has lost the characteristics that give it the ability to support life – it is "dead"
• Roles of soil


  • Serve as media for growth of all kinds of plants
  • Modify the atmosphere by emitting and absorbing gases (carbon dioxide, methane, water vapor, and the like) and dust
  • Provide habitat for animals that live in the soil (such as groundhogs and mice) to organisms (such as bacteria and fungi), that account for most of the living things on Earth
  • Absorb, hold, release, alter, and purify most of the water in terrestrial systems
  • Process recycled nutrients, including carbon, so that living things can use them over and over again
  • Serve as engineering media for construction of foundations, roadbeds, dams and buildings, and preserve or destroy artifacts of human endeavors
  • Act as a living filter to clean water before it moves into an aquifer
• Soil profile


  The horizons (O, A, E, B, C, R) that form the layers of a soil

  
• Soil horizons


  • O - Mostly organic matter such as decomposing leaves
  • A - Mostly minerals from parent material with organic matter incorporated
  • E - Leached of clay, minerals, and organic matter, leaving a concentration of sand and silt particles
  • B - Rich in minerals that leached (moved down) from the A or E horizons and accumulated here
  • C - The deposit at Earth's surface from which the soil developed
  • R - Bedrock, a mass of rock that forms the parent material for some soils

  
• Weathering


  The breaking down or dissolving of rocks and minerals on the surface of the Earth
• Water, ice, acids, salts, plants, animals, and changes in temperature are all agents of weathering
• Weathering and erosion constantly change the rocky landscape of Earth. Weathering wears away exposed surfaces over time. The length of exposure often contributes to how vulnerable a rock is to weathering.
• Weathering is often the first step in the production of soils. Tiny bits of weathered minerals mix with plants, animal remains, fungi, bacteria, and other organisms.
• Types of weathering


  • Mechanical weathering
  • Chemical weathering
  • Biological weathering
• Factors of soil formation

  • Time
  • Climate
  • Parent material
  • Topography and relief
  • Organisms
• The formation of soils is a continuing process and generally takes several thousand years for significant changes to take place.
• Climate, particularly temperature, precipitation and frost action have a profound influence on the soil forming processes which occur within a region.
• Weathering


  • Mechanical weathering
  • Chemical weathering
  • Biological weathering
• Soil formation


  Interaction of five major factors: time, climate, parent material, topography and relief, and organisms
• Time


  • Soil formation is a continuing process and generally takes several thousand years for significant changes to take place
• Climate


  • Determines the nature of the weathering processes and the rates of these chemical and physical processes
  • Directly affects the type of vegetation which in turn affects soil forming processes related to vegetation
• Parent material


  • Determines the mineralogical composition and contributes to the physical and chemical characteristics of the soil
  • Influences the rate at which soil forming processes take place
• Topography and relief


  • Shape of the land surface, slope and position on the landscape greatly influence the kinds of soils formed
  • Soils on higher elevations and sloping areas are generally excessively drained or well drained
  • Soils at lower elevations often have a seasonal high water table at a shallow depth
• Organisms


  • All living organisms actively influence the soil forming process
  • Micro-organisms promote acid conditions and change soil chemistry
  • Microbial animals decompose organic materials
  • Larger animals mix the soil and change its physical characteristics
  • Man's activities can have the most beneficial or most detrimental impact on soil forming processes
• Soil structure types


  • Granular
  • Blocky
  • Prismatic
  • Columnar
  • Platy
  • Single Grain

  
• Granular


  Resembles cookie crumbs, usually less than 0.5 cm in diameter, commonly found in surface horizons where roots have been growing
• Blocky


  Irregular blocks usually 1.5 - 5.0 cm in diameter
• Prismatic


  Vertical columns of soil that might be a number of cm long, usually found in lower horizons

  
• Columnar


  Vertical columns of soil that have a salt "cap" at the top, found in soils of arid climates
• Platy


  Thin, flat plates of soil that lie horizontally, usually found in compacted soil
• Single Grained


  Soil is broken into individual particles that do not stick together, always accompanies a loose consistence, commonly found in sandy soils
• Soil types


  • Sand
  • Clay
  • Silt
  • Peat
  • Chalk
  • Loam
• Sandy soil


  • Light, warm, dry and tend to be acidic and low in nutrients
  • Have quick water drainage and are easy to work with
  • Quicker to warm up in spring than clay soils but tend to dry out in summer and suffer from low nutrients that are washed away by rain
  • Addition of organic matter can help improve nutrient and water holding capacity
• Clay soil


  • Heavy soil type that benefits from high nutrients
  • Remain wet and cold in winter and dry out in summer
  • Made of over 25 percent clay, hold a high amount of water
  • Drain slowly and take longer to warm up in summer, can often test gardeners
• Silt soil


  • Light and moisture retentive soil type with a high fertility rating
  • Well drained and hold moisture well
  • Prone to washing away with rain
  • Adding organic matter can bind the particles into more stable clumps
• Peat soil


  • High in organic matter and retains a large amount of moisture
  • Very rarely found in a garden and often imported to provide an optimum soil base for planting
• Chalk soil


  • Can be either light or heavy but always highly alkaline due to the calcium carbonate or lime
  • Will not support the growth of ericaceous plants that require acidic soils
• Loam soil


  • Mixture of sand, silt and clay that are combined to avoid the negative effects of each type
  • Fertile, easy to work with and provide good drainage
  • Depending on predominant composition can be either sandy or clay loam
  • Considered a gardener's best friend but still benefit from topping up with additional organic matter