Lithosphere & Soil Profiling Notes
Soil Profiling: Texture, Structure, & Horizons
Day 1 & 2 Overview
Objectives:
Characterize soil by texture, structure, NPK content, and pH.
Characterize soil at different horizons.
Da Vinci Quote
"We know more about the movement of celestial bodies than about the soil underfoot."
The lesson questions if we truly know more about the soil we step on compared to celestial bodies.
Soil Formation
Rocks break down through weathering into smaller pieces.
These pieces mix with minerals, organic matter, water, and air to form soil.
Approximately half of soil is fragmented/decomposed rocks (mineral particles) and humus (decayed organic matter).
The other half is pore space containing air and water.
Humus:
Essential source of plant nutrients.
Enhances water retention.
Pore spaces are important for air and water flow, which plants need to live along with nutrients.
Water contains dissolved nutrients for plant growth and moisture for chemical reactions.
Air provides oxygen and carbon dioxide for microorganisms and plants.
Soil Profile
Provides information about texture, structure, mineral/nutrient content, and layers.
Soil Texture
Refers to the proportions of different particle sizes.
Affects the soil's ability to retain/transmit water and air which are essential for plant growth.
Soil Particle Types
Sand: Largest particles.
Silt: Medium-sized particles.
Clay: Smallest particles.
Soil Characteristics Based on Particle Size
Sandy Soil:
Light, warm, and dry.
May drain water rapidly and dry out quickly.
Tend to be acidic and low in nutrients.
Clay-rich Soil:
Heavy soil with poor water drainage, leading to long-lasting puddles.
Can hold onto nutrients.
Silty Soil:
Light and moisture retentive.
Prone to washing away with rain.
Can hold limited nutrients.
Soil Texture Categories
Based on the proportion of sand, silt, and clay.
Important for determining agricultural potential and engineering characteristics.
Soil-Texture Diagram
Used to categorize soils based on the percentage of sand, silt, and clay.
Example: A soil with 30% clay, 35% sand, and 55% silt is categorized as clay loam soil.
Loam Soils
Generally considered best for plant life support.
Better nutrient storage and moisture characteristics than clay or sand-rich soils.
Soil Structure
Soils form clumps known as peds.
Peds create structures that can be platy, prismatic, blocky, or granular.
Soil texture affects ease of agriculture and vulnerability to erosion.
Soil structure influences permeability and porosity, affecting nutrient movement to plant roots.
Soil Structure Types and Characteristics
Granular: slow infiltration rate, eases the tillage of land, good structure for planting and germination, highly altered garden soils with high organic matter
Blocky: moderate water infiltration, common in subsoil and in surface soils high in clay content.
Prismatic: moderate water infiltration, commonly in subsoils, the vertical cracks are due to the downward movement of roots and water.
Platy: slow water infiltration, root growth is hindered due to the compacted structure.
Soil pH Level and NPK Content
Chemical factors that influence the agricultural function of soil.
pH Level
Measure of how acidic or basic a substance is, ranging from 0 (most acidic) to 14 (most basic).
Most soils have a pH between 3.5 and 10.
Higher rainfall areas: pH 5 to 7.
Drier areas: pH 6.5 to 9.
Right pH level is necessary for healthy plant growth.
Soil pH Classifications
6.5 to 7.5: Neutral.
Over 7.5: Alkaline (base).
Less than 6.5: Acidic.
Less than 5.5: Strongly acidic.
NPK Content
Nitrogen (N), Phosphorus (P), and Potassium (K) are primary macronutrients.
Essential for plant life.
Nitrogen (N):
Constituent of proteins and nucleic acids.
Phosphorus (P):
Constituent of proteins and nucleic acids.
Potassium (K):
Regulates processes like water movement (osmosis).
Necessary for the quality of harvested plant products.
Optimal plant growth depends on soil texture, structure, and sufficient nutrient supply.
Farmers need to know the NPK content to determine fertilizer needs.
Amount of NPK should be adequate, not too high or low.
Too low NPK: Hampered growth and low yields.
Too high NPK: Disturbed plant growth and adverse effects on quality.
NPK Benefits
Plants process these minerals into useable nutrients for animals and humans.
Nitrogen:
3.2% of the human body as a component of proteins, nucleic acids, etc.
Humans and animals cannot get nitrogen directly from the air or soil.
Phosphorus:
Essential to all living things, found in DNA and RNA.
Essential for metabolism, energy transfer, and bone formation.
1.0% of the human body.
Soil Horizons
Soil-forming process occurs from the surface downward.
Composition, structure, and color change with depth.
Noticeable layering of soil parallel to the surface.
Soil Horizon Characteristics
O Horizon (Topsoil):
Mostly organic materials (plants and animals).
Upper portion: Plant litter and recognizable organic debris.
Lower portion: Partially decayed organic matter (humus).
Packed with microscopic life (bacteria, algae, fungi, insects).
Organisms contribute oxygen, carbon dioxide, and organic acids.
A Horizon:
Mostly mineral matter.
Humus generally present.
High biological activity.
E Horizon (Zone of Eluviation and Leaching):
Light-colored layer with little organic matter.
Eluviation and leaching occur.
B Horizon (Subsoil; Zone of Accumulation):
Materials carried from E horizon accumulate here.
Water retention enhanced due to deposited fine clay particles.
Hardpan (compact and impermeable layer) may form.
C Horizon:
Partially altered parent material.
Materials are converting into soil but resemble parent material/bedrock.
R Horizon (Bedrock):
Unweathered parent materials.
Terms
Eluviation: Finer soil particles carried away as water percolates through the soil layer (Horizon E).
Leaching: Depletion of soluble materials as water carries them downward to deeper layers.
Solum: Horizons where soil-forming processes are active (O, A, E, and B). Zone where living roots, plants, and animals are mostly found.
Parent Material: Source of weathered mineral matter from which soils develop.
Observable Differences Among Soil Horizons
Color:
Deeper horizons are lighter in color.
Topsoil is darker than lower horizons.
Some horizons have a red shade.
Particle Size:
Lower the soil horizon, the larger the particles.
Depth:
Lower horizons are deeper.
O horizon is the shallowest.
Appearance of soil horizons may vary due to climate and the types of animals and plants present.
Soil is essential for plant growth, providing habitat, recycling nutrients, and supporting structures.
Importance of Soil
Primary source of food through plants.
Provides habitat to many organisms.
Serves as the foundation for structures.
Plays a major role in recycling nutrients and water.
Investigating the Lithosphere II Soil Types
Learning Objectives
Determine plant types for different types of soil.
Identify ways to improve poor soil.
Enumerate the importance of soil.
Soil Re-Planting Inference
The lesson prompts reflection on the appearance of a plant before and after re-planting, and what actions might have been taken during the process.
Soil Types and Plant Growth
Plants obtain food and water from the soil, absorbing nutrients through their roots.
Soil supports plants and prevents erosion.
Farmers cultivate and fertilize soil to prepare for planting.
Different crops grow in different types of soil.
Soil Types, Characteristics, Plant Growth, and Improvement
Clay Soil:
Characteristics: Fine, dense particles that do not allow water to soak in easily; absorbs water slowly; holds moisture for a long time.
Plants that Grow: Rice, lettuce, pechay, mustard, cabbage, broccoli, corn, and squash.
Ways to Improve: Add organic manure, tree bark, decayed leaves to improve structure and drainage.
Sandy Soil:
Characteristics: Gritty, drains easily, dries out fast, warms up quickly, holds fewer nutrients.
Plants that Grow: Carrots, radishes, pineapples, potatoes, tomatoes, lettuce, beans, cucumber, and watermelons.
Ways to Improve: Add well-rotted manure or compost (fruit and vegetable peelings, dry leaves, plant branches); mix vermicompost.
Silty Soil:
Characteristics: Larger particles than clay but smaller than sand; fertile; found beside riverbanks.
Plants that Grow: Different plants, fruits, vegetables, trees, and shrubs.
Ways to Improve: Add composted organic matter to improve drainage, structure, and nutrients.
Loam Soil:
Characteristics: Balanced mixture of sand, silt, clay, and humus; soft but gritty; excellent drainage; retains water and nutrients; crumbly.
Plants that Grow: Tomatoes, peppers, green beans, cucumbers, onions, lettuce, corns, okra, radishes, eggplants, carrots, root vegetables, leafy vegetables, strawberries, blackberries, and blueberries.
Ways to Improve: Regular replenishing with organic matter; crop rotation and compost application.
Most plants can adapt and thrive in different types of soil.
Importance of Soil
Essential for growing food.
Home to beneficial soil microbes.
Habitats for organisms (insects, moles, worms, etc.).
Used to make homes (bricks, cement, adobes) and pottery.
Filters surface water.
Used in medicine (antibiotics).
Regulates Earth’s temperature.
Stores history (artifacts).
Summary
Clay, sandy, silt, and loam are the four types of soil.
Clay soil is ideal for shallow-rooted plants.
Sandy soil is ideal for plants with taproots.
Silty soil is nutrient-rich and found near bodies of water.
Loam is the ideal soil for cultivating crops.
Poor soil has less nutrients and organic matter; can be improved with decayed materials, compost, and organic fertilizers.
Soil is fundamental to life, an essential natural resource, and a major component of most ecosystems.