5.1 Introduction to Soil Systems Flashcards
Soil
composed of mineral and organic matter, air, and water, that forms the uppermost layer of the Earth’s surface and is capable of supporting plant life
Soil texture
The relative proportions of sand, silt, and clay particles in soil.
Clay
The smallest soil particles.
High porosity (holds water), but low permeability (slow to drain)
Silt
Medium-sized soil particles (between clay and sand) that feel smooth and powdery.
Often river deposited.
Sand
The largest soil particles, which feel gritty and allow for good drainage.
Porosity
The measure of the void spaces in soil, affecting its ability to hold water and air.
Permeability
Relates to drainage.
The ability of soil to transmit water and air through its pores.
Horizons
The distinct layers of soil that form a soil profile.
Soil profile
A vertical section (cross-section) of soil that shows all its horizons.
“O” horizon
The topmost soil layer, rich in organic matter and decomposed material.
Humus lies above it, not within it.
“A” horizon
The topsoil layer, rich in organic material and minerals, where most plant roots grow.
“B” horizon
The subsoil layer, where minerals leached from above accumulate.
“C” horizon
The layer of partially disintegrated and weathered parent material beneath the B horizon.
Bedrock
The solid rock layer beneath the soil layers.
Sometimes called the “R” layer
Parent material
The underlying geological material from which soil forms.
Soil texture triangle
A diagram that classifies soil types based on the proportions of sand, silt, and clay.
Loam
A balanced soil type with roughly equal parts of sand, silt, and clay, preferred by farmers for its fertility and workability.
Soil texture preferred by farmers
Loam is preferred for its ideal balance of drainage, nutrient retention, and ease of cultivation.
Physical soil surface crust
Protects soil from erosion and moisture loss but can inhibit seedling emergence.
Biological soil surface crust
A community of living organisms on the soil surface (lichens, algae, mosses) that stabilizes soil and reduces erosion.
Rainsplash erosion
The detachment and movement of soil particles caused by the impact of raindrops.
Hoof action
the impact and movement of an animal’s hooves on the ground, which can influence soil compaction, aeration, and erosion
Soil compaction
The compression of soil particles (often by grazing stock or vehicle tires) that reduces pore space, hindering root growth and water infiltration.
Jar method
A technique to analyze soil texture by mixing soil with water in a jar, allowing particles to settle into layers of sand, silt, and clay.
Why is soil important?
Soil is essential for plant growth, water filtration, carbon storage, and as a habitat for organisms.
Soil ecosystem services
- nutrient cycling
- water filtration and storage
- carbon sequestration
- erosion management
- plant growth support
Minerals in soil
Soil contains essential minerals like nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur needed for plant and animal life.
Aggregate
A cluster of soil particles that bind together, creating pores for air and water movement.
Bolus
A cohesive mass of soil formed by kneading and squeezing, used to assess soil texture by feel.
Slaking
The breakdown of soil aggregates when exposed to water, indicating soil structure stability.
Eluviation
involves the leaching of materials such as clay, iron, or organic matter from one horizon to another, usually from the upper horizons to the lower ones, leaving the upper horizons depleted of these substances.
Topsoil vs subsoil
Topsoil: The uppermost soil layer, rich in organic matter and nutrients, essential for plant growth.
Subsoil: The layer beneath the topsoil, containing minerals leached from above but less organic matter.
Alluviation
the process of deposition of sediment by flowing water, typically in the form of alluvium, which consists of materials such as silt, sand, clay, and gravel, often creating fertile land areas like riverbanks, floodplains, and deltas.
Eluviation vs illuviation
eluviation involves the removal of materials from upper horizons, while illuviation involves the deposition of materials in lower horizons, both driven by the movement of water through the soil profile.
Lithosphere vs pedosphere
the lithosphere is the rigid outer layer of the Earth’s crust and mantle involved in geological processes, the pedosphere is the layer of soil and living organisms that interact with the atmosphere and hydrosphere to support life on Earth
Determining the moisture content of soil
measuring the weight difference of a soil sample before and after drying it in an oven to evaporate the water content.
