Weathering and Soils

Regolith- The layer of weathered rock fragments beneath the soil and above the bedrock (solid rock). ← Soil ← Regolith ← Bedrock

Soil = minerals, water, gases, organic mtl. Soil Components Regolith is the basis for soil… Soil = minerals, water, gases, organic mtl.

humus- dark, organic material made of decayed animal and plant remains Found just beneath the vegetation Important part of soil- provides nutrients! ← Humus

3 types of rock materials make up soil- classified by the size of the particles. Sand (0.05 – 2 mm in dia.) Silt (0.002 to 0.05 mm) Clay (<0.002 mm in dia.) The amounts of each of these components depends on the parent rock!

Soil Facts Lichens-die add organic nutrients to soil Slowly renewable resource- 1cm=15 or more years Filters water-infiltrationleaching (diluting nutrient rich layers) into aquifers/surface runoff Decomposer Carbon Sink Biogeochemical Cycles!!! PROBLEM: Erosion

Soil Triangle and Example

Clay soils- high percentage of clay Come from rocks with a lot of feldspar… Hold a lot of water Doesn’t drain well

Silty soils Very fine particles, have a gritty feel Erodes easily Often found on riverbanks

Sandy soils- high percentage of sand Come from weathered granite and rocks with a lot of quartz Doesn’t hold water, drains quickly

Transported vs. Residual soil Transported soil = moved from original location, will have a different composition than the bedrock below Residual soil = soil that rests on top of its parent rock

Soil profile Cross-section of layers of soil and the bedrock beneath

Horizons (Residual Soil) A horizon – topsoil B horizon – subsoil (minerals, clay, humus) C horizon – partially weathered bedrock (regolith) O- Organic E- no organics R- bedrock Top 2 layers-bacteria, fungi, worms, insects

Transported soils DO NOT have horizons, they are found in layers or unsorted depending on how they were transported!

Soil and Climate Humid tropical climates: a lot of rain + high temps = chemical weathering Desert climates: minimal rain, high temps= minimal weathering Temperate climates: temperature range between cool and warm, rainfall varies = both types of weathering

Tropical Soils Laterites – Thick but infertile soils produced in tropical climates Contains irons and other minerals that do not dissolve Topsoil often thin Organic matter constantly added

Desert Soils Thin Made up of mostly rock fragments (evidence of mechanical weathering) Arctic soil similar

Temperate Soils All three horizons can reach a thickness of several meters. 2 main types: 1. pedalfer- contains clay, quartz, and iron compounds, forms in places receiving 65cm + of rain per year (Ex. states east of Mississippi and Gulf Coast states)

2. pedocal- contains large amounts of calcium carbonate, formed in places receiving less than 65 cm of rain per year.

Soil types around the world correspond to climates…

Topography and Soil Too flat = poor drainage On slopes- soil is thick and fertile at the bottom and thin and nutrient-poor on the slope. Ideal soil conditions = fairly flat but with good drainage