-What defines a soil?
“the naturally occurring, unconsolidated mineral and organic material at the earth’s surface that provides an environment for
weathered layer of the earth’s crust
mineral and organ
Recently referred to as the earth’s critical zone
Role in controlling the earth’s environment and thus in affecting the sustainability of life on the planet
-Soil as an environmental interface
Exchange of matter and energy.
Interface between the biosphere, the hydrosphere, the atmosphere and the lithosphere.
Air, biota organic, minerals, water is what soil is composed. Water will interact with hydrosphere, biota organic with
biosphere, air with atmosphere, and minerals with lithosphere. Litho Greek for rock.
Soils may also be covered with water to a depth of up to 0.5 m as in coastal tidal marshes or inland water areas
-Soil forming factors
Biota, time, parent material, climate, topography
Vertical cut in soil. O,A,E,B,C,
Different layers are called horizons.
Soil consist of O,A,E,B and parent material is C horizon
Solids are spatially arranged in a very complex way, forming tortuous pore spaces. Porosity 30-60%
Soil organic mater composition-Humic substances 50%, living biomass 4, nonhumic substances 30, macroorganic matter 16
Soil biomass composition- Macrofauna22, microorganisms 70, roots 8
Bacteria important in numbers fungi in biomass
-Porous medium-Solid phase, liquid phase (soil solution) Gaseous phase(soil atmosphere)
Unsaturated zone=vadose zone. Water and air occupy pores
Saturated zone water fills all pores. Groundwater table in between zones.
Interfaces-Solid/liquid, liquid/gas, gas/solid
Soil properties- texture, structure.
Particles >2mm are not considered as soil materials
Texture-relative percentage of sand silt, and clay
Sand:50-2μm in diameter.
More larger pores so less water retention
Clay: smaller than 2μm.
Smaller pores so more water retention.
Primary silicate mineral- minerals that are identical to what is in the parental material
Secondary silicate mineral- chemically changed with time.
Quartz consist of feldspar and mica
Sand-primary minerals, feels gritty, low specific area, not cohesive
Specific surface area- related to volume. The smaller the object the larger the specific surface area of the object.
Clay-secondary minerals, swells/shrink, negatively charged, plastic behavior, feels sticky when wet, very high specific area.
Charge will repel anions and attract cations.
Silt-primary minerals, feels like flour, medium specific area, retain water beter than sand but drain better than clay.
-Textural triangle- refer to picture
Loamy soils are the best conditions for agricultural purposes
Particle density Ps: weight of solid particles/volume of solid particles (usually considered as 2.65 g cm^-3; Quartz)
Dry bulk density Pd: dry weigh of soil/volume of the soil
Organic soil pd~0.8