Soil Resources Chapter 7 PDF

Chapter 7 PAGE 229 – 251 (1st Edition) 181 – 208 (2nd Edition)  LEARNING OBJECTIVES Appreciate the interaction and integration of subsystems that influence the soil system. Describe the major components of a soil and how they vary to produce different soil types and; Cite an...

Chapter 7 PAGE 229 – 251 (1st Edition) 181 – 208 (2nd Edition)  LEARNING OBJECTIVES Appreciate the interaction and integration of subsystems that influence the soil system. Describe the major components of a soil and how they vary to produce different soil types and; Cite an examples of major human impacts on soils. SOIL Dynamic natural body that is capable of supporting vegetative cover. It contains chemical solutions, gases, organic refuse, flora, and fauna. Soil responds to climate change. “Skin of the Earth”  SOIL In fact, because soils integrate these major subsystems so well, they are sometimes considered as a separate system called the pedosphere. (Greek: pedon, means ground) Credit: Know Soil, Know Life book/Soil Science Society of America Soil – Intersecting All Spheres on Earth  SOIL In fact, because soils integrate these major subsystems so well, they are sometimes considered as a separate system called the pedosphere. (Greek: pedon, means Soil isground) also home to numerous living organisms forming the environment in which they live, both above and below the ground surface. The life forms that live in a soil play significant roles in the development and characteristics of a soil, and through human population growth and expanding civilizations, potentially negative impacts on soils have increased dramatically. MAJOR SOIL COMPONENTS Inorganic Materials Soil Water Soil Air Organic Matter  Inorganic Materials Soil contains varying insoluble materials ---rock fragments and minerals that will not readily dissolve in water. Soil also contains soluble minerals, which supply dissolved chemicals held in solution.  Inorganic Materials Common elements of Earth’s surface rocks: silicon, aluminum, oxygen, iron Weathering- breaking down of underlying rocks Soil Fertilization- process of adding nutrients or other constituents in order to meet the soil conditions that certain plants require.  SOIL WATER The original source of water is precipitation. “Capillary water”, serves as a stored water supply for plants. Caliche- cement like layer built up from evaporating soil water Caliche  SOIL WATER Hygroscopic water - Soil water found as a very thin film, invisible to naked eyes, that is bounded to the ground by electrical forces. It does not move through the soil, and it does not supply plants with the moisture they need. Gravitational water - Percolates down through a soil under the force of gravity.  SOIL WATER Water table - the level below which all available spaces are filled with water Several conditions: Amount of precipitation Time since it fell Evaporation rates Space available for water storage How easily the water can move through the soil  SOIL WATER Leaching - Depicting zone where all open spaces are saturated Eluviation - Downward removal of soil components by water Illuviation- Deposition by water in the subsoil Stratification- Leaching and eluviation both strongly influence the characteristic layered changes with depth  SOIL AIR 50% consists of spaces between soil particles and dumps. Dumps- aggregate of soil particles Aggregate  ORGANIC MATTER Soil contains organic matter in addition to minerals, gases, and water. The decayed remains of plant and animal materials, partially transformed by bacterial action, are collectively humus. Humus- important catalyst in chemical reactions that help plants to extract soil nutrients.  COLOR Most visible, but may not be important attribute. Soils vary in color from black to brown to red, yellow, gray, and near white. Dark brown or black soils are often referred to as rich.  COLOR Soils red and yellow typically indicate the presence of iron. Light-gray or white soil indicates that iron has been leached out; same color indicates a high proportion of calcium or salts. Reddish- indicated oxidation Blue/Silver/Gray- soil is reduced; oxygen has been removed White- denotes that calcium carbonate or salts may be present in the soil Black- indicated high amount of organic material  TEXTURE Refers to the particle size (or distribution of sizes) that make lip a soil. Clayey soils- the dominant size of particle is clay; having diameter of 0.002 millimeter. Silty soil- dominant is silt; 0.002 and 0.05 millimeter.  TEXTURE Sandy soils- the dominant size of particle is sand-sized particles; having diameter of 0.05 and 2.0 millimeter. Triangular graph- used to discern different classes of soil textures based on plot percentages for each soil grade Soil grade- as sand, silt, and clay are called  SOIL STRUCTURE 26 SOIL STUCTURE In most soils, particles clump into distinctive masses known as soil peds, which give a soil a distinctive structure. Porosity- amount of space that may contain liquid Permeability- the rate at which fluids such as water can pass through ACIDITY AND ALAKALINITY It is an important aspect of soil chemistry to know its departure from acidity to alkalinity. Levels of acidity and alkalinity are measured on the pH scale. DEVELOPMENT OF SOIL HORIZONS Soil development begins when plants and animals colonize rocks or deposits of rock fragments, the parent material on which soil will form. Once organic processes begin among mineral particles or rock fragments, differences begin to develop from the surface down through the parent material. Soil profile – the vertical cross-section of a soil from the surface down to the parent material. SOIL HORIZONS Within their soil profiles, well-developed soils typically exhibit several distinct layers called soil horizons, that are distinguished by their physical and chemical properties. Soil horizons are designated by a set of letters that refer to their composition, dominant process, and/or position in the soil profile.  SOIL HORIZONS O horizon – layer of organic debris and humus A horizon – topsoil E horizon – named for the action of strong eluvial processes B horizon – zone of accumulation where much of the materials removed from the A and E horizons are deposited C horizon – weathered parent material from which the soil has developed either fragments of the bedrock or deposits of rock material R horizon – unchanged parent material  What is parent material? Rock material that has undergone some weathering and change but not enough to be called true soil, as it is not capable of sustaining plant life. 32  FORMATION OF SOIL All soil originated as rocks. Powerful forces act on the rocks to break them down into smaller fragments (weathering). Water penetrates the cracks in the rock and when it freezes the water acts as a wedge to split the rock. 33 FACTORS AFFECTING THE SOIL FORMATION Climate Organic matter Relief Parent Material Time By HANS JENNY Climate Temperature, Rainfall, etc.  Climatic Differences Hot – Dry Desert Cold – Dry Antarctica Hot – Wet Tropics Cold – Wet Northern Canada Warm - Humid Warm - Dry  Organic Accumulation of plant and animal debris – generally in wet environments Relief AKA TOPOGRAPHY  Relief, Topography or Slope Degree of slope – erosion, stability Location on the slope – water relations Source: Soil! Get the Inside Scoop, SSSA Time Degree of soil formation General Time Sequence SOIL FORMING REGIMES LATERIZATION - A soil-forming regime that occurs in humid tropical and subtropical climates as a result of high temperatures and precipitation. - a soil type is known as laterite meaning “brick-like” (generally reddish in color from iron oxide SOIL FORMING REGIMES PODZOLIZATION - it occurs mainly in the high middle latitudes where the climate is moist with short, cool, summer and long, severe winters. The coniferous forests of these climate regions are an integral process. SOIL FORMING REGIMES -occurs in region where evapotranspiration significantly exceeds precipitation - important in the climate region where climate penetration is shallow SOIL FORMING REGIMES Salinization - the concentration of the salt in the soil, often detrimental for plant growth  Gleization - it occurs in poorly drained areas under cold and wet environmental conditions.  SOIL AS A CRITICAL NATURAL RESOURCE It is clearly the responsibility of all of us who enjoy the agricultural products of farms, ranches, and orchads and appreciate the natural beauty of earth’s diverse biomes – to help to protect our valuable soils. Soil erosion, soil depletion, and the mismanagement of land are problems that we should have great concern about in the world today. We should be aware that these problems have reasonable solutions.