Introduction to Soil and its Components

• Module 1 discusses soil, its formation, and its components.
• The inquiry question addresses the components of rocks and soils.
• Key concept: M1.2.6 explains soil formation by looking at the interactions of atmospheric, geologic, hydrologic, and biotic processes.

The Complex System of Soil

• Soil has non-living (abiotic) and living (biotic) parts.
• Natural ecosystems depend on soil for their nutrients, which allow plants to grow.
• The soil is home to diverse ecosystems of microorganisms and invertebrates.
• Minerals, water, air, and organic matter make up soil.
• Parent material for soil can be a rock like basalt, or sediment like sand, or silt, left by a flood

Pore Spaces in Soil

• Air and water are located in the spaces between mineral grains called pore spaces.
• Mineral particle size affects pore size. Large particles have more pore space.
• Soil becomes waterlogged when pore spaces are full of water, leading to plant death because cellular respiration can't happen due to lack of oxygen.
• Microbes grow in the pore spaces an provide binding surfaces for mineral nutrients.

Classifying Soil: Grains

• Soil grain size and shape are related to those of sedimentary rock.
• Grain size ranges: pebbles (4-64 mm), granules (2-4 mm), Coarse sand (0.5-2 mm), Medium sand (0.25-0.5 mm), Fine sand (0.06-0.25 mm), Silt (0.004-0.06 mm), Clay (<0.004 mm)

Classifying Soil: Porosity

• Porosity is the percentage of pore space in soil, ranging from 10% to 70%.
• Porosity impacts how well water drains through the soil.

Classifying Soil: Texture

• Proportions of sand, silt, and clay determine a soil’s texture.
• Soil texture influences drainage, nutrient binding, and ease of cultivation.
• A soil texture triangle is used to determine a soil's grade

Soil Texture Determination Steps

• Sieve to remove coarse material, if there isn't a sieve, or the soil is wet, remove the fragments.
• Knead a soil sample with water until it is no longer sticking to the fingers. A ball (bolus) cant be made if the soil is very sandy
• Press the soil between your fingers to form a hanging ribbon approx 2-3mm in thicccccness
• The feel and behaviour and the ribbon will determines the texture
• Do not strictly base it on the ribbon length

Classifying Soil: Chemistry

• Soil's chemistry is dictated by the parent rock material and actions of the hydrosphere, biosphere, and atmosphere.
• Soil color reflects the parent material and processes involved in its production where basalt may weather to provide iron, which reacts with oxygen from the air to create yellow, orange or red colors in a soil.
• Soil pH affects availability of essential elements, plants adapt to the pH levels of the soils in which they grow.
• pH changes may limit nutrients or release toxic substances, where Nitrogen, sulfur, and phosphorus are among the key nutrients for plant growth

pH and its Influences

• Soil pH is impacted by water movement of chemicals (leaching) as well as organic material and fertilizers.
• Soil pH affects availability of essential elements for plants.
• Leaching describes when water washes substances/minerals from the upper to lower soil layers.

Soil Horizons Define

• Soil horizons are parallel to the surface.
• The O horizon has organic matter and humus.
• The A horizon, or "top soil," is vital for surface biology.
• The B Horizon, is a "subsoil" with a light brown color thanks to leached minerals.
• The C Horizon featuers weathered and unweathered rock.
• The R Horizon is bedrock and the base material for the layers above.

Leaching

• Leaching influences soil horizon development.
• Nutrients, salts, and silts are leached between layers.

The Leaching Process

• Soil profile: occurs when water moves downward when there is rain/irrigation where it dissolves substances such as nitrates, potassium, and calcium.
• Process may lead to depletion of essential nutrients in upper soil layers which are important for plant growth; a build up of leached minerals in lower layers (B horizon) will occur.

Climate Factors

• Climate impacts the weathering/leaching of minerals and decomposition of organic matter.

The Weathering Process

• Soil forms from rock breakdown through weathering where weathering is a biological, chemical, or physical process.
• Physical weathering breaks rocks mechanically through temperature changes, abrasion, and frost.
• Chemical weathering breaks rocks through reactions with water, air, or other chemicals.
• Biological weathering occurs when living things break down rocks where plant roots grow into cracks and animals burrow bringing air and water.

Time

• Weathering of bedrocks, material deposition, biological cycles, and water leaching all require time.
• Soil horizons and layers also need time to rise to their proper levels