Untitled Quiz

Introductory Soil Concepts

• Soil is derived from the Latin word "solum," meaning floor.
• Soils are natural bodies in which plants grow.
• Soil is a mixture of minerals, organic matter, gases, liquids, and a myriad of microorganisms.

Functions of Soil

• Supports plant growth as an anchor and water reservoir.
• Soil properties affecting plant growth include texture, aggregate size, porosity (permeability), and water holding capacity.
• Soils store and supply nutrients needed for plant growth.
• Clay and organic matter (OM) content directly influence soil fertility.
• Soils regulate water supplies, absorbing and storing moisture.
• Water movement (infiltration) depends on texture, physical condition (structure), and vegetative cover.
  • Coarse (sandy) soils allow rapid infiltration but have less storage.
  • Fine (clayey) soils have better water storage but slower infiltration rates.
  • Organic matter enhances water retention in all soils.
• Recycles raw materials through decomposing dead organisms by soil flora and fauna (bacteria, fungi, insects).
  • Factors influencing decomposition rate include physical environment, chemical makeup, water, oxygen, and temperature.
  • Nitrogen content in organic matter impacts decomposition rate.
• Provides a habitat for soil organisms.
  • Microorganisms are primary decomposers, transforming dead material for use by other organisms.
• Essential elements needed by decomposers are air, food, and water suitable physical environment (suitable habitat).
  • Microorganisms are usually aerobic, but some are anaerobic.
  • Soil porosity and pore structure affect the organisms' ability to thrive.
• Crucial medium in landscaping and engineering.
• Soil science has two main branches: edaphology and pedology.
  • Pedology focuses on soil formation, morphology, and classification.
  • Edaphology focuses on the influence of soils on organisms.
  • Edaphology is concerned with soils' influence on living things, specifically plants.

Soil Formation

• Soil formation (pedogenesis) is a combined effect of physical, chemical, biological, and anthropogenic processes on the parent material.
• The parent material is the mineral material from which a soil forms.
• Rocks—igneous, sedimentary, and metamorphic—are sources of soil mineral materials and plant nutrients (excluding N, H, and C).
• Typical soil minerals include quartz (SiO2), calcite (CaCO3), feldspar (KAlSi3O8), and mica (biotite).
• Classification of parent material:
  • Residual materials are minerals that weathered in place.
  • Transported materials originate from water, wind, ice, or gravity.
  • Cumulose material is organic matter that accumulates in place.
• Soil forming processes are:
  • Weathering is the breakdown of rock into smaller particles.
    • Physical weathering (disintegrating) changes particle size only.
    • Chemical weathering (decomposing) alters the composition.
  • Agents of physical weathering include heat, cold, freezing and thawing, erosion by streams, and wind.
  • Chemical weathering involves water and various chemicals creating acids breaking down the material. Examples include:
    • Solution - dissolves salts.
    • Carbonation - reactions of CO2 with water and minerals like calcite.
    • Oxidation - inclusion of oxygen in a mineral.

Soil Forming Factors

• Climate

  • Effective precipitation and temperature influence chemical, physical, and biological processes.
  • Climate is crucial in soil formation. Soils manifest distinctive characteristics of climate zones.
  • Direct influences of climate include accumulation of lime in low rainfall areas, formation of acid soils in humid areas, erosion on steep hillsides, and downstream deposition of eroded materials.

• Topography (relief)

  • Inclination (slope), elevation, and orientation of the terrain.
  • Topography impacts precipitation, runoff, and soil formation/erosion.
  • Slope and aspect influence soil moisture and temperature.

• Organisms (biological factors)

  • All living things (plants, animals, microorganisms) affect soil formation.
  • Soil mesofauna and microorganisms mix soils through burrowing and create pores, allowing water and gases to move.
  • Plant roots open channels, allowing nutrients to reach deeper soil layers.
  • Legumes and grasses contribute organic matter and microorganisms.
  • Humans impact soil formation by removing vegetation (leading to erosion) and tillage, which restarts soil formation processes.

• Time

  • Soil is continuously changing.
  • It takes hundreds to thousands of years for fertile soil layers to form.

• Parent material

  • Primary material forming the soil.
  • Parent materials include bedrock, organic matter, old soil surfaces, and deposits from water, wind, glaciers, or volcanoes.
  • Some soils weather directly from the underlying rock; those are called residual soils.

Soil Properties

• Soil texture

  • Relative proportions of sand, silt, and clay particles.
  • Particle size determines properties like porosity, permeability, and water holding capacity.
    • Sand: large pores, rapid infiltration, low water holding capacity.
    • Silt: intermediate pore size, slower infiltration, moderate water holding capacity.
    • Clay: small pores, slow infiltration, high water holding capacity.
  • Useful grouping of soil textures: coarse (sands), medium (loams), fine (clays).
  • Soil texture triangle displays the proportions of sand, silt, and clay in different soils.

• Soil structure

  • Aggregation of soil particles into distinct units.
  • Influences aeration, water movement, and root penetration.
    • Granular: sphere-shaped particles, common in surface horizons rich in organic matter.
    • Prismatic and blocky: aggregates from shrinking and cracking of clay.
    • Platy: horizontal layers, from silted materials.
    • Stability of aggregates may impact cultivation techniques and plant growth.
  • Grade of Structure (describing its stability)
    • 0 - structureless, massive.
    • 1 - weak and poorly formed peds.
    • 2 - moderate and well-formed, but not distinct in undisturbed soil.
    • 3 - strong and durable, weakly adhered peds. -Maintaining soil structure:
    • Avoid tilling when wet.
    • Add lime and fertilizers.
    • Grow grasses and legumes.

• Soil Color

  • Observable characteristic used for classification and identification.
  • Inferences about soil drainage, fertility, and weathering rates can be drawn.

• Soil density

  • Mass per unit volume.
    • Particle density: density of the solid components per unit volume of soil particles.
    • Bulk density: considering the whole soil volume, including pores.
    • In general, soils with lower bulk densities are better for plant growth and water infiltration.

• Porosity

  • Empty spaces between soil particles filled with air and water.
  • Macro pores in spaces between aggregates
  • Micro pores in spaces between particles of aggregates.
    • Influences water infiltration and drainage.