soil formation and properties

what is soil

highly variable, 3D, open chemical/physical, system covering terresttrial earth (distinct horizons/thicknesses)

• composed of minerals, organic matter, water, air

biology of a soil

activity of organisms utilizing sunlight and chemical energy

water in soil

enables chemical reactions (transport medium)

temperature in soil

impacts chemical reaction rates, modifies available water through ET

parent material of soil

impacts nutrients available 

photosynthesis

plants produce food from sunlight (converts solar energy into sugar and releases oxygen)

respiration

microbes and plants convert food into energy (releases CO2 into the environment (air/soil)

acidification

respiration products release hydrogen ions into the soil solution

primary minerals

have not experienced serious chemical/structural alteration since their crystallization 

• inherited from parent material

  • usually found in sand/silt fractions of soil

  • ex: silicates, oxides of iron, zircon, titanium, phosphates

secondary minerals

recrystallized or transformed products of the chemical breakdown/alteration of primary minerals

• usually found in clay/fine silt fractions (particles size decrease during weathering)

• ex: alumino-silicates, oxides/hydroxides, carbonates, sulfates, amorphous materials

weathering

H+ reacts with another mineral structure, releasing a cation and forming clay minerals

soil composition

air: 20/30%

water: 20/30%

organic material: 5%

mineral: 45%

mineral (inorganic components)

• large particles (stones, cobbles) may be of mixed minerology 

• smaller particles usually composed of single material (sand, silt, clay) 

soil organic matter SOM

residue created by the opposing reactions of carbon inputs (plant production) and carbon losses (microbial respiration)

soil air

soil pores are either filled with soil water or soil air

• higher moisture content (100% humid)

• CO2 concentration often 100sX higher

• oxygen content much lower (5-10% vs 20)

soil organic matter does not…

improve soil structure 

you are digging a pit in the african savanna, what kind of soil are you going to find?

alfisol

on a field trip in the Pacific Northwest, you hike through conifer forests, crossing parts of the columbia flood river plain, and stopping to rest in a grass land. what kinds of soil are you going to find?

spodosol, inceptisol, mollisol