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Questions and Answers
What characterizes an Inceptisol in terms of soil horizons?
What characterizes an Inceptisol in terms of soil horizons?
Which soil type is considered the ultimate result of weathering?
Which soil type is considered the ultimate result of weathering?
How does the presence of climate affect soil profiles?
How does the presence of climate affect soil profiles?
Which factors can lead to variations in soil profiles?
Which factors can lead to variations in soil profiles?
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What happens to layer R in the Ultisol stage of soil formation?
What happens to layer R in the Ultisol stage of soil formation?
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What effect does organic matter have on soil properties?
What effect does organic matter have on soil properties?
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How is soil water significant to plant growth?
How is soil water significant to plant growth?
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What is the relationship between soil air volume and water volume?
What is the relationship between soil air volume and water volume?
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What is the process of weathering in soil formation?
What is the process of weathering in soil formation?
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What defines a soil horizon?
What defines a soil horizon?
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Which process involves the transformation of materials such as weathering and organic matter breakdown in soil formation?
Which process involves the transformation of materials such as weathering and organic matter breakdown in soil formation?
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What does the E horizon primarily involve?
What does the E horizon primarily involve?
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Which horizon is rich in humus and consists of partly decomposed organic material?
Which horizon is rich in humus and consists of partly decomposed organic material?
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What represents unaltered parent material in soil profiles?
What represents unaltered parent material in soil profiles?
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Which soil order is described as 'recently developed'?
Which soil order is described as 'recently developed'?
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What does the term 'eluviation' refer to in the context of soil horizons?
What does the term 'eluviation' refer to in the context of soil horizons?
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Which layer of the soil profile typically lacks organic material and resembles the underlying rock?
Which layer of the soil profile typically lacks organic material and resembles the underlying rock?
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What kind of materials are added to the soil profile in the addition process?
What kind of materials are added to the soil profile in the addition process?
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Which of the following definitions accurately describes soil?
Which of the following definitions accurately describes soil?
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From an agricultural point of view, what is the primary role of soil?
From an agricultural point of view, what is the primary role of soil?
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Which component is NOT a part of the composition of soil?
Which component is NOT a part of the composition of soil?
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What is the importance of parent materials in soil?
What is the importance of parent materials in soil?
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Which factor contributes to the variability of mineral matter in soil?
Which factor contributes to the variability of mineral matter in soil?
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What aspect defines soil from an engineering perspective?
What aspect defines soil from an engineering perspective?
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Which statement does not describe a component necessary for soil formation?
Which statement does not describe a component necessary for soil formation?
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Why are living forms essential in soil?
Why are living forms essential in soil?
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Study Notes
GEOD 301: SOILS & BIOGEOGRAPHY - LECTURE 1
- Course: GEOD 301: Soils & Biogeography
- Lecture: 1
- Topic: Definition and Composition of Soil
- Lecturer: Dr. Peter B. Obour
- Email: [email protected]
-
Objectives:
- Define soil
- Understand soil composition
- Understand soil formation
- Examine soil profiles
Definitions
- Foth (1978): Soil is the loose surface of the earth.
- MacDonald (2003): Soil is the uppermost layer of mineral and organic matter found on the earth's surface.
- Buckman and Brady (1960): Soil is a dynamic natural body on the earth's surface in which plants grow, composed of mineral and organic materials and living forms.
Definitions (Continued)
- Dynamic natural body: Soil is constantly changing and is not static.
- Surface of the earth: It is the uppermost layer, not water bodies.
- Organic, inorganic, & living forms: Soil must contain organic material (humus), inorganic matter, and living things (fauna).
- Parent materials: Soil forms from the breakdown of pre-existing rock and minerals.
- Organic materials (e.g., humus): Essential organic component of soil
Soil Composition
- Water: 25%
- Air: 25%
- Mineral matter: 45%
- Organic matter: 5%
Mineral Matter
- Variable in size: Ranges from small rock fragments to microscopic clay particles.
- Electron microscope: Needed to see some very small particles.
Organic Matter
- Partially synthesized plant and animal residues: Partially decayed plants and animals.
- Continuous breakdown through soil microorganisms: Natural decomposition process.
- Soil properties and health: Influences soil properties and plant growth.
Soil Water
- Major component for plant growth: Essential to plant health.
- Held with soil pores: Water is held within the spaces between soil particles.
- Dissolves salts: Creation of a soil solution where nutrients are available for plants.
Soil Air
- Pore space: Space between soil particles.
- Air and water: Pore space is occupied by air and water.
- Inverse relationship with water: More water = less air.
- Significant influence: Affects plant and root growth and soil microorganisms.
Soil Formation (Pedogenesis)
- Weathering: Breakdown of rocks, minerals, and soils through physical, chemical, and biological processes.
- Parent materials: Weathering begins with the breakdown of bedrock or transported sediments; these are parent materials.
Soil Horizons
- Soil horizon: Layer in the soil with distinct properties that vary from layers above and below.
- Soil profile: Vertical sequence of soil horizons at a given location.
Soil Profile Processes
- Transformations: Involve weathering and organic matter decomposition.
- Translocations: Movement of materials between horizons, mainly through water and soil organisms.
- Additions: Materials enter the profile from external sources such as organic materials, atmospheric dust, or soluble salts.
- Losses: Materials leave the profile through erosion.
A Typical Soil Profile (from Ricklefs)
- O horizon: Loose, easily recognizable organic debris. Dead organic material.
- Oe horizon: Partially decayed organic material.
- Oa horizon: Fully decomposed organic material.
- A horizon: Mineral horizon rich in humus (dark, organic material).
- E horizon: Light-colored zone of maximum leaching (loss of minerals and organic materials).
- EB/BE horizon: Transition zone between E and B horizons.
- B horizon: Subsurface horizon characterized by accumulation of clays, iron, and aluminum oxides.
- BC horizon: Transition zone between B and C horizons.
- C horizon: Weathered parent material (partially broken down rock).
- R horizon: Unaltered parent material (bedrock).
Soil Profile Types
- Entisol: Recent soil with little development.
- Inceptisol: Beginning stages of soil formation.
- Alfisol: Intermediate stage of weathering, B and C horizons are present.
- Ultisol: Advanced stage of weathering, very little R layer, and B and C and E horizons are present.
Diversity of Soil Profiles
- Not all horizons present in every soil: Some soils lack the E horizon.
- Soil forming factors: Variations in soil profiles are due to differences in climate, parent material, biota, topography, and time.
- Further study needed: Additional research on variety of soil profiles.
Variations in Soil Horizons
- Climate: Affects weathering rate, leaching, and erosion.
- Parent material: (rock type). Type of rock impacts the amount of weathering.
- Biota: (organisms and vegetation) Influences decomposition and other processes.
- Time: Soil gradually develops over time.
- Topography: Slope impacts erosion rates and water movement.
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Description
Explore the foundational concepts of soil in this first lecture of GEOD 301: Soils & Biogeography. Understand the definition, composition, and dynamic nature of soil, as well as its importance in plant growth. This lecture sets the stage for understanding soil profiles and formation processes.
