4.2 Soil Formation & Erosion
Weathering
- Breakdown of rocks into smaller pieces - Physical (wind, rain, freezing/thawing of ice) - Biological (roots of trees crack rocks) - Chemical (acid rain, acids from moss/lichen) - Weathering of rocks = soil formation - Broken into smaller and smaller pieces - Carried away and deposited by erosion
What is Soil?
- Mix of geologic (rock) and organic (living) components Sand, silt, clay - Humus: main organic part of soil (broken down biomass like leaves, dead animals, waste, etc.) - Nutrients: ammonium, phosphates, nitrates - Water and Air - Living Organisms
Soil Horizons OABC - Layer of... - Function
- O-Horizon: layer of organic matter (plant roots, dead leaves, animal waste, etc) on top of soil - Provides nutrients and limits H2O loss to evap. - A-Horizon: aka topsoil; layer of humus (decomposed organic matter) and minerals from parent material - A-Horizon has most biological activity (earthworms, soil microbes) breaking down organic matter to release nutrients - B-Horizon: aka subsoil; lighter layer below topsoil, mostly made of minerals w/little to no org. matter - Contains some nutrients - C-Horizon: least weathered soil that is closest to the parent material, sometimes called bedrock
Effects on Soil Form. - Parent material - Topography - Climate - Organisms
- Parent material: soil pH, nutrient content - Topography: steep slope = too much erosion; more level ground = deposition - Climate: warmer = faster breakdown of org. matter; more precip. = more weathering, erosion + deposition - Organisms: Soil organisms like bacteria, fungi, worms breakdown organic matter
Describe the characteristics and formation of soil.
- Soils are formed when parent material is weathered, transported, and deposited. - Soils are generally categorized by horizons based on their composition and organic material. - Soils can be eroded by winds or water. Protecting soils can protect water quality as soils effectively filter and clean water that moves through them.
Erosion
- Transport of weathered rock fragments by wind and rain - Carried to new location and deposited (deposition)
Compaction:
- compression of soil by machines (tractors, bulldozers, etc.), grazing livestock, and humans reduces ability to hold moisture - Dry soil erodes more easily - Dry soil supports less plant growth, less root structure, leading to more erosion
Loss of Topsoil:
- tiling (turning soil for ag.) + loss of vegetation disturb soil and make it more easily eroded by wind and rain - Loss of top soil dries out soil, removes nutrients + soil organisms that recycle nutrients
Design an investigation to measure the effect that climate has on soil formation. Identify the independent variable and dependent variable in your experiment
...
Soil Formation - From Below v. Above
From below - Weathering of parent material produces smaller, and smaller fragments that make up geological/inorganic part of soil - Sand, silt, clay - Minerals From above - Breakdown of organic matter adds humus to soil Erosion deposits soil particles from other areas, adding to soil
Soil Degradation:
The loss of the ability of soil to support plant growth
Plants:
anchors roots of plants and provides water, shelter, nutrients (N, P, K, Mg) for growth
Water:
filters rainwater + runoff by trapping pollutants in pore spaces + plant roots. Clean water enters groundwater + aquifers
Nutrient Recycling:
home to decomposers that break down dead organic matter + return nutrients to the soil
Habitat:
provides habitat for org. like earthworms, fungi, bacteria, moles, slugs
Nutrient Depletion:
repeatedly growing crops on the same soil removes key nutrients (N, P, K, Na, Mg) over time - Reduces ability to grow future crops