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

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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