Soil Science Basics

What is Soil?

• Soil is a medium that consists of a mixture of sediment, minerals, organic matter, air, gases, liquids, organisms, and microorganisms.
• It provides the fundamental ecosystem and essentials for plant life and all life.

Soil Functions

• Provides space and medium for plants to grow.
• Provides water storage and water purification.
• Provides a home for many organisms, especially microorganisms.
• Participates in all major biogeochemical cycles (e.g., phosphorous, nitrogen, and carbon cycles).

Soil Composition

• Varies in gas content due to microorganisms, decomposing organic matter, and plants.
• Different conditions and amounts of organic matter in soils from different regions affect gas content.
• Space between particles of sediment determines how easily gases and liquids flow through it.

Soil Types

• Four main types: sand, silt, clay, and loam.
• Each type provides different circumstances and microclimates (e.g., water content, permeability, and aeration).

Soil Structure and Development

• Develops and accumulates from basic components through multiple processes (e.g., sediment weathering, erosion, organic matter introduction, decomposition, and water introduction).
• Not all soils are the same, and base sediments determine the type of ecosystem.

Soil Layers

• Soil profile consists of many layers of sediments beneath a top layer of soil, each layer being a different soil horizon.
• Top layer's sediment matrix can be composed of sand, silt, clay, or loam, while underlying layers consist of compacted layers of sediments before reaching bedrock.

Sand

• Sediment with tiny weathered rock particles between 62 microns (very fine) and 2 millimeters (very coarse) in size.
• Coarsest, largest, and loosest of soil classifications.
• Provides easy drainage for water, but is not very nutritious for growing plants.

Silt

• Sediment with particles between 4 and 62 microns in size.
• Holds onto water more and longer than sand, allowing for nutrients to remain.
• Very common in swampy and muddy conditions.

Clay

• Sediment with particles less than 4 microns in size.
• Fine-grained silt that holds onto water well, but lacks drainage and aeration.
• Often found deep below layers of topsoil.

Loam

• Combination of sand, silt, and clay.
• Provides the best of both worlds for plant life (drainage, water storage, and aeration).
• Commonly used for farming and found all around the world.

Differences in Structure and Arrangement

• Soil varies in particle size, shape, and arrangement (e.g., granular, platy, and columnar structures).
• Granular soil provides good drainage and aeration.
• Platy soil has horizontal layering, decreasing drainage.
• Columnar soil is dense and compacted, with slow drainage.

Uses of Soil

• Fundamental for ecosystem survival (e.g., forest ecosystems).
• Important for agricultural industry (food and fiber production).
• Used as a building material (e.g., concrete, construction sites).
• Understanding soil is important for maintaining proper soil conditions for future generations.