Soil Composition, Formation and Types

• Soil is a crucial natural resource that supports plant life and ecosystems
• A complex mixture of minerals, organic matter, water, and air

Soil Composition

• Minerals derive from weathering
• Organic matter consists of decomposed plant and animal material
• Water and air fill spaces between soil particles

Soil Formation

• Weathering represents the breakdown of rocks into smaller particles
• Erosion is the movement of soil particles by wind, water, or ice
• Organic matter accumulates from the decomposition of plants and animals

Soil Horizons

• The O horizon, the uppermost layer, is rich in organic matter and humus
• The A horizon, or topsoil, is a mixture of minerals and organic matter, fertile and suitable for plant growth
• The B horizon, or subsoil, accumulates minerals leached from above
• The C horizon consists of partially weathered parent material
• The R horizon is the bedrock

Soil Types

• Sandy soil has large particles, good drainage, but poor water retention
• Silty soil has medium-sized particles, good water retention, and nutrient content
• Clay soil has small particles, poor drainage, but high water retention and nutrient content
• Loamy soil is a balanced mixture of sand, silt, and clay, ideal for plant growth

Soil Properties

• Texture refers to the proportion of sand, silt, and clay particles
• Structure describes the arrangement of soil particles into aggregates
• Porosity refers to the amount of pore space
• Permeability is the rate at which water flows through the soil
• Fertility is the ability to support plant growth

Soil Organisms

• Bacteria, fungi, and earthworms live in the soil
• They decompose organic matter, cycle nutrients, and improve soil structure

Soil Conservation

• Contour plowing reduces soil erosion by plowing along the land's contours
• Terracing reduces soil erosion by creating level platforms on slopes
• Crop rotation maintains soil fertility by planting different crops in succession
• Cover cropping protects soil from erosion by planting a crop

Soil Pollution

• Fertilizers and pesticides can contaminate the soil
• Industrial waste and sewage sludge can introduce heavy metals and other pollutants
• Soil pollution can harm soil organisms and reduce soil fertility

Importance of Soil

• It serves as a medium for plant growth, providing support, water, and nutrients
• It acts as a habitat for organisms, contributing to biodiversity
• Facilitates nutrient recycling, decomposition of organic matter, and cycling of essential elements
• It provides water storage and filtration, regulating water flow and improving water quality
• It's an engineering medium, supporting infrastructure and construction

Soil Texture Triangle

• A graphical tool used to determine soil textural classes based on percentages of sand, silt, and clay
• A ternary diagram where each side represents the percentage of sand, silt, or clay, ranging from 0% to 100%
• Find percentages of two soil separates, draw lines inward from axes parallel to the opposite side; the intersection indicates the soil textural class

Weathering Types

• Physical weathering involves mechanical breakdown into smaller pieces without changing chemical composition
• Chemical weathering involves alteration of the chemical composition of rocks
• Biological weathering involves the breakdown of rocks by living organisms

Humus

• Dark, organic material formed from decomposition
• Improves soil structure, water retention, and nutrient availability
• It's rich in nutrients such as nitrogen, phosphorus, and potassium

Leaching

• The process by which water-soluble substances are washed down through the soil
• It can remove nutrients from the topsoil, depositing them in the subsoil
• Excessive leaching leads to nutrient depletion and soil degradation

Soil pH

• A measure of the acidity or alkalinity
• Affects the availability of nutrients to plants
• Most plants grow best in slightly acidic to neutral soils

Soil Color

• An indicator of composition and properties
• Dark soils are generally rich in organic matter
• Red soils contain iron oxide

Importance of Earthworms

• They aerate the soil by creating channels
• They mix the soil, bringing nutrients to the surface
• Their castings are rich in nutrients
• Improve drainage

Soil Erosion

• The process by which soil is detached and transported by wind, water, or ice
• Leads to loss of topsoil, reduced soil fertility, and water pollution
• Caused by deforestation, overgrazing, and poor farming practices

Types of Soil Erosion

• Sheet erosion is the removal of a thin layer of soil from a large area
• Rill erosion is the formation of small channels or rills
• Gully erosion is the formation of large channels or gullies
• Wind erosion is the removal of soil particles by wind

Nutrient Cycling

• The movement of nutrients through the soil, plants, and atmosphere
• Nutrients are absorbed by plants and returned through decomposition

Soil Conservation Practices

• No-till farming involves planting crops without plowing
• Windbreaks: Planting rows of trees reduces wind erosion
• Strip cropping involves planting different crops in alternating strips to reduce soil erosion
• Conservation tillage reduces the amount of tillage to minimize soil disturbance

Soil Degradation

• The decline in soil quality due to human activities
• It can lead to reduced crop yields, water pollution, and loss of biodiversity
• Caused by erosion, compaction, salinization, and pollution

Soil Compaction

• Increases soil density and reduces pore space
• Restricts root growth, reduces water infiltration, and increases runoff
• Caused by heavy machinery and livestock

Salinization

• The accumulation of salts
• It can inhibit plant growth and reduce crop yields
• Caused by irrigation with saline water and poor drainage

Soil Amendments

• Materials improve physical, chemical, or biological properties
• Examples include compost, manure, lime, and fertilizers

Compost

• Decomposed organic matter
• Improves soil structure, water retention, and nutrient availability

Manure

• Animal waste
• Provides nutrients and improves structure

Fertilizers

• Supply essential nutrients
• They can be synthetic or organic
• Overuse can lead to water pollution

Lime

• Raises the pH of acidic soils
• It makes nutrients more available

Sustainable Soil Management

• Practices that maintain or improve soil quality while minimizing environmental impacts
• Examples include crop rotation, conservation tillage, and integrated pest management

Importance of Soil Biodiversity

• The variety of organisms living in the soil
• It contributes to nutrient cycling, decomposition, and disease suppression
• Soil pollution and habitat destruction can reduce it

Soil Surveys

• Systematic examinations of soil properties and distribution
• Used to classify soils, map soil types, and provide information for land-use planning

Remote Sensing of Soil

• The use of satellite imagery to study soil properties
• Provides information on soil moisture, vegetation cover, and erosion

Precision Agriculture

• Using technology to manage soil and crops more efficiently
• Monitoring soil conditions, applying inputs precisely, and optimizing crop yields

Learn about the vital natural resource that sustains plant life. This module focuses on soil composition, formation processes such as weathering and erosion, and distinctive soil horizons. Explore the characteristics of varied soil types from sandy to clay.