Abiotic (soil)

• Abiotic factors


  The non-living chemical and physical parts of the environment that affect living organisms and the functioning of the ecosystem
• Physical components


  • Energy
  • Climate
  • Raw materials
  • Living space
• Chemical components


  Sources of essential nutrients (e.g. proteins, lipids, carbohydrates)
• Soil


  Complex mixture of minerals, water, air, organic matter, and countless organisms that are the decaying remains of once-living things
• Roles of soil


  • Serve as media for growth of all kinds of plants
  • Modify the atmosphere by emitting and absorbing gases and dust
  • Provide habitat for soil organisms
  • Absorb, hold, release, alter and purify water
  • Process and recycle nutrients
  • Serve as engineering media
  • Act as a living filter to clean water
• Soil horizons


  • O-Horizon (organic materials)
  • A-Horizon (humus layer)
  • E-Horizon (leached of clay, minerals, and organic matter)
  • B-Horizon (subsoil, site of mineral deposition)
  • C-Horizon (broken bedrock)
  • R-Horizon (compacted and cemented layer)
• Soil color


  Influenced by mineral composition, water, and organic content
• Soil needs only about 5% organic material to appear black when wet
• Soil color is also a reflection of its age and the temperature and moisture characteristics of the climate
• Soil texture


  Refers to the proportion of sand, silt and clay sized particles that make up the mineral fraction of the soil
• Topsoil


  • High amount of organic matter, more loose and crumbly texture, dark brown to black color due to humus
• Subsoil


  • More compact and less aerated, higher proportions of sand and less organic matter, higher clay content, color ranges from yellow, reddish, to grayish
• Organic matter content


  Darker soil colors (dark brown to black) due to presence of humus
• Moisture content


  Wet soils appear darker than dry soils
• Mineral composition


  Iron oxides (hematite, magnetite) impart red and black colors respectively
• Soil texture


  Coarser soils (sandy) tend to be lighter in color, while finer soils (clayey) can be darker
• Parent material


  Soils inherit colors from their parent material (e.g. basalt vs limestone)
• Soil age and weathering

  Older, more weathered soils tend to be darker in color
• Climate


  Humid climates enhance organic matter decomposition and leaching, leading to darker soils. Arid climates may lead to lighter-colored soils
• Primary sources of organic matter

  • Plant residues (leaves, stems, roots)
  • Animal waste (manure, urine, carcasses)
  • Microbial biomass (bacteria, fungi)
• Temperature


  Higher temperatures accelerate organic matter decomposition and weathering, leading to faster soil formation and nutrient cycling
• Parent material


  Mineral composition of parent rock influences soil mineral content and texture
• Topography


  Steeper slopes are more prone to erosion, leading to thinner soils with less organic matter. Gentle slopes or flat areas tend to accumulate more soil and organic matter.
• Elevation


  Higher elevations often have thinner soils due to slower weathering and increased erosion
• Water


  Soils with high water table may be saturated, leading to anaerobic conditions that slow decomposition. Well-drained soils have better aeration and different microbial activity.
• Soil pH


  Affects microbial activity and nutrient availability
• Dark brown to black soils

  Indicate high organic matter content, healthy microbial activity, and fertile environment for plant growth
• Gleyed or bluish-gray soils


  Indicate poor drainage and waterlogged conditions, which can inhibit root growth and reduce nutrient availability
• Red soils


  High in iron oxides, suggest well-drained and highly weathered soils
• White or light gray soils

  High in silica or calcium carbonate, may indicate low organic matter and potentially low fertility