GGY 130 1st Edition Lecture 20Chapter 12: Soils -Soil and Regolith• Soil-Thin layer on top of Earth’s crust (~15-20 cm) -Complex mixture of minerals, organic matter, organisms, gases, and liquids-Regolith• Inorganic matter that results from rock weathering-Soil Components• Inorganic Materials -Sand, Silt, and Clay • Organic Matter-Small percent of soil volume (<5%) -Living and dead organisms, partially or completely decomposed organisms• Litter: leaves, other dead plant parts on soil surface• Humus: black gelatinous organic matter which results from decomposed residues• Soil Air-Pores (>50%)-Air in soil is saturated with moisture-Air in soil is rich in carbon dioxide • Soil Water -Rainfall, snowfall-Gravitational water: (free water) is pulled down into the soil by gravity -Eluviation and Illuviation-Capillary water: (water of cohesion) moisture which is held on soil particle surfaces by surface tension-Water performs a number of important functions• Dissolving essential nutrients for plants roots • Helps complete necessary chemical reactions • Mixes soil particles• Soil colour -Describes nature and capabilities of soil-Black.dark brown soil has large humus content-Red/yellow indicates high iron oxide content -Grey/blue indicates poor drainage• Munsell Soil Colour Chart -Value: darkness of colour (reflects organic matter content)-Chroma: strength of colour (reflects iron oxide content)• Soil Texture -Sand, Silt, and Clay -Feel for particle size-Soil Text Triangle indicates the percentage of sand, silt, and clay particles in the soil-The best soil texture is “Loam” - a mixture of 40% sand, 40%silt, and 20% clay• Soil Chemistry -In soils, all nutrients are provided to plants in solution-Highly acidic solution• Nutrients dissolves away too rapidly for plants to absorb them-Highly alkaline solution• Ineffective in dissolving minerals and releasing nutrients-pH scale (0-14)-Soil Profiles• O (Organic litter; not typical for soils to have)• A (Topsoil; minerals and organic, coarse texture, where seeds germinate)• E (Leaching/eluvial layer; concentration of sand and silt particles)• B (Subsoil; mineral/illuviation layer)• C (Unconsolidated regolith; no organic matter)• R (Bedrock; no weathering activity)• Solum: The true soil that includes only the top four