Soil Science Overview

Soil as an Interface

• Soil represents a boundary where the solid earth, atmosphere, hydrosphere, and biosphere interact.

Components of Soil

• Consists of 45% mineral matter, 25% air, 25% water, and 5% organic matter.

Regolith vs. Soil

• Regolith is the layer of weathered rock and mineral fragments covering Earth's surface; soil specifically supports plant growth.

Texture and Grain Size

• Sand has larger, coarser grains, while clay comprises smaller, finer particles.

Importance of Soil Texture

• Texture significantly affects soil's ability to retain and transmit water and air, which are crucial for plant growth.

Loam Definition

• Loam is a balanced mixture of sand, silt, and clay, ideal for nutrient retention and moisture.

Soil Structure

• Describes the arrangement of soil particles; platy and spheroidal structures slow nutrient movement; prismatic and blocky structures allow moderate water infiltration.

Controls of Soil Formation

• Factors include climate, organisms, parent material, topography, and time.

Soil-Forming Processes

• Operate primarily from the surface downwards, impacting layer development over time.

Soil Horizons in Temperate Regions

• Temperate regions feature five horizons: O (organic), A (topsoil), E (eluviation), B (illuviation), and C (parent material).

Composition of Soil Layers

• Topsoil consist of O and A horizons; the solum includes O, A, E, and B horizons, also called true soil, while the subsoil is primarily the B horizon.

Soil Formation Features

• Eluviation is the leaching out of materials; zone of accumulation refers to deposits in the B horizon; hardpan forms from compacted clay layers.

Purpose of Soil Classification

• Soil Taxonomy categorizes soils based on their physical and chemical properties for understanding and analysis in contexts like agriculture.

Soil Taxonomy System

• Features 12 named soils organized into six hierarchical categories; names derived from Latin and Greek; useful for agriculture, not engineering evaluations.

Soil Erosion

• A natural process where water and wind transport soil components, resulting in potential displacement of topsoil.

Factors Influencing Soil Erosion Rate

• Influenced by soil characteristics, climate, slope angle, and type of vegetation.

Global Soil Regions

• Reference to worldwide distribution of 12 soil orders, shaped by climatic influences, with poorly developed soils at higher latitudes.

Human Impact on Soil Erosion

• Practices like windbreaks, terracing, contour plowing, and crop rotation are used to mitigate erosion effects.

Detrimental Effects of Soil Erosion

• Sedimentation can lead to reservoir capacity loss and costly dredging; chemical pollution affects water quality.

Ore Formation through Weathering

• Secondary enrichment occurs via chemical weathering, where desirable minerals are concentrated in lower zones; examples include bauxite for aluminum.

Horizon Definition

• A specific layer within a soil profile.

Soil Texture Explanation

• Defined by the proportion of clay, silt, and sand, significantly impacting water retention and air transmission.

Soil Profile Description

• A vertical cross-section displaying different soil horizons and the parent material.

Erosion vs. Weathering

• Erosion involves material transport by agents like water or wind, while weathering is the breakdown and decomposition of rocks.

Factors Necessary for Soil Formation

• Requires parent material, time, climate, and organic contributions from plants and animals; topography affects soil development.

Human Activity and Soil Erosion

• Common activities like farming and logging accelerate erosion, leading to sedimentation in waterways and contamination of water supplies.