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Questions and Answers
What role does soil color help to determine?
What role does soil color help to determine?
Soil depth does not influence the size of water and nutrient storage capacity available to plants.
Soil depth does not influence the size of water and nutrient storage capacity available to plants.
False
What is the average particle density for mineral soils?
What is the average particle density for mineral soils?
2.65 g/cm³
The condition of poor aeration due to accumulated water above a clay sub-soil layer is called __________.
The condition of poor aeration due to accumulated water above a clay sub-soil layer is called __________.
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Match the following soil density types with their descriptions:
Match the following soil density types with their descriptions:
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Which of the following practices helps maintain or increase organic matter in the soil?
Which of the following practices helps maintain or increase organic matter in the soil?
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Heavy metals in the soil can decrease particle density.
Heavy metals in the soil can decrease particle density.
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List one consequence of high bulk density in the soil.
List one consequence of high bulk density in the soil.
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What is one major consequence of soil compaction?
What is one major consequence of soil compaction?
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Soil compaction helps improve water quality by reducing surface runoff.
Soil compaction helps improve water quality by reducing surface runoff.
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Name one effect of maintaining good soil structure.
Name one effect of maintaining good soil structure.
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Excessive traffic over the land leads to a compacted soil mass with _______ pores collapsing.
Excessive traffic over the land leads to a compacted soil mass with _______ pores collapsing.
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Match the grade of soil structure with its description:
Match the grade of soil structure with its description:
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Which of the following practices can help maintain soil structure?
Which of the following practices can help maintain soil structure?
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Soil with high compaction retains air more efficiently.
Soil with high compaction retains air more efficiently.
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What is one negative impact of intensive cultivation on soil?
What is one negative impact of intensive cultivation on soil?
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What is a consequence of soil compaction on plant growth?
What is a consequence of soil compaction on plant growth?
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Granular soil structure is beneficial for planting because it provides a poor environment for root growth.
Granular soil structure is beneficial for planting because it provides a poor environment for root growth.
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What is the effect of granular soil structure on water drainage?
What is the effect of granular soil structure on water drainage?
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Soil structures that are approximately spherical and ideal for planting are called ___ structures.
Soil structures that are approximately spherical and ideal for planting are called ___ structures.
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Match the following soil structures with their characteristics:
Match the following soil structures with their characteristics:
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Which of the following is a disadvantage of prismatic and blocky soil structures?
Which of the following is a disadvantage of prismatic and blocky soil structures?
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A higher organic matter content leads to better granular soil structure.
A higher organic matter content leads to better granular soil structure.
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Compact soil may lead to a ____ drainage of water and limited access to nutrients for plants.
Compact soil may lead to a ____ drainage of water and limited access to nutrients for plants.
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Study Notes
Introductory Soil Concepts
- Soil is derived from the Latin word "solum," meaning floor.
- Soils are natural bodies in which plants grow.
- Soil is a mixture of minerals, organic matter, gases, liquids, and a myriad of microorganisms.
Functions of Soil
- Supports plant growth as an anchor and water reservoir.
- Soil properties affecting plant growth include texture, aggregate size, porosity (permeability), and water holding capacity.
- Soils store and supply nutrients needed for plant growth.
- Clay and organic matter (OM) content directly influence soil fertility.
- Soils regulate water supplies, absorbing and storing moisture.
- Water movement (infiltration) depends on texture, physical condition (structure), and vegetative cover.
- Coarse (sandy) soils allow rapid infiltration but have less storage.
- Fine (clayey) soils have better water storage but slower infiltration rates.
- Organic matter enhances water retention in all soils.
- Recycles raw materials through decomposing dead organisms by soil flora and fauna (bacteria, fungi, insects).
- Factors influencing decomposition rate include physical environment, chemical makeup, water, oxygen, and temperature.
- Nitrogen content in organic matter impacts decomposition rate.
- Provides a habitat for soil organisms.
- Microorganisms are primary decomposers, transforming dead material for use by other organisms.
- Essential elements needed by decomposers are air, food, and water suitable physical environment (suitable habitat).
- Microorganisms are usually aerobic, but some are anaerobic.
- Soil porosity and pore structure affect the organisms' ability to thrive.
- Crucial medium in landscaping and engineering.
- Soil science has two main branches: edaphology and pedology.
- Pedology focuses on soil formation, morphology, and classification.
- Edaphology focuses on the influence of soils on organisms.
- Edaphology is concerned with soils' influence on living things, specifically plants.
Soil Formation
- Soil formation (pedogenesis) is a combined effect of physical, chemical, biological, and anthropogenic processes on the parent material.
- The parent material is the mineral material from which a soil forms.
- Rocks—igneous, sedimentary, and metamorphic—are sources of soil mineral materials and plant nutrients (excluding N, H, and C).
- Typical soil minerals include quartz (SiO2), calcite (CaCO3), feldspar (KAlSi3O8), and mica (biotite).
- Classification of parent material:
- Residual materials are minerals that weathered in place.
- Transported materials originate from water, wind, ice, or gravity.
- Cumulose material is organic matter that accumulates in place.
- Soil forming processes are:
- Weathering is the breakdown of rock into smaller particles.
- Physical weathering (disintegrating) changes particle size only.
- Chemical weathering (decomposing) alters the composition.
- Agents of physical weathering include heat, cold, freezing and thawing, erosion by streams, and wind.
- Chemical weathering involves water and various chemicals creating acids breaking down the material. Examples include:
- Solution - dissolves salts.
- Carbonation - reactions of CO2 with water and minerals like calcite.
- Oxidation - inclusion of oxygen in a mineral.
- Weathering is the breakdown of rock into smaller particles.
Soil Forming Factors
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Climate
- Effective precipitation and temperature influence chemical, physical, and biological processes.
- Climate is crucial in soil formation. Soils manifest distinctive characteristics of climate zones.
- Direct influences of climate include accumulation of lime in low rainfall areas, formation of acid soils in humid areas, erosion on steep hillsides, and downstream deposition of eroded materials.
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Topography (relief)
- Inclination (slope), elevation, and orientation of the terrain.
- Topography impacts precipitation, runoff, and soil formation/erosion.
- Slope and aspect influence soil moisture and temperature.
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Organisms (biological factors)
- All living things (plants, animals, microorganisms) affect soil formation.
- Soil mesofauna and microorganisms mix soils through burrowing and create pores, allowing water and gases to move.
- Plant roots open channels, allowing nutrients to reach deeper soil layers.
- Legumes and grasses contribute organic matter and microorganisms.
- Humans impact soil formation by removing vegetation (leading to erosion) and tillage, which restarts soil formation processes.
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Time
- Soil is continuously changing.
- It takes hundreds to thousands of years for fertile soil layers to form.
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Parent material
- Primary material forming the soil.
- Parent materials include bedrock, organic matter, old soil surfaces, and deposits from water, wind, glaciers, or volcanoes.
- Some soils weather directly from the underlying rock; those are called residual soils.
Soil Properties
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Soil texture
- Relative proportions of sand, silt, and clay particles.
- Particle size determines properties like porosity, permeability, and water holding capacity.
- Sand: large pores, rapid infiltration, low water holding capacity.
- Silt: intermediate pore size, slower infiltration, moderate water holding capacity.
- Clay: small pores, slow infiltration, high water holding capacity.
- Useful grouping of soil textures: coarse (sands), medium (loams), fine (clays).
- Soil texture triangle displays the proportions of sand, silt, and clay in different soils.
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Soil structure
- Aggregation of soil particles into distinct units.
- Influences aeration, water movement, and root penetration.
- Granular: sphere-shaped particles, common in surface horizons rich in organic matter.
- Prismatic and blocky: aggregates from shrinking and cracking of clay.
- Platy: horizontal layers, from silted materials.
- Stability of aggregates may impact cultivation techniques and plant growth.
- Grade of Structure (describing its stability)
- 0 - structureless, massive.
- 1 - weak and poorly formed peds.
- 2 - moderate and well-formed, but not distinct in undisturbed soil.
- 3 - strong and durable, weakly adhered peds. -Maintaining soil structure:
- Avoid tilling when wet.
- Add lime and fertilizers.
- Grow grasses and legumes.
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Soil Color
- Observable characteristic used for classification and identification.
- Inferences about soil drainage, fertility, and weathering rates can be drawn.
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Soil density
- Mass per unit volume.
- Particle density: density of the solid components per unit volume of soil particles.
- Bulk density: considering the whole soil volume, including pores.
- In general, soils with lower bulk densities are better for plant growth and water infiltration.
- Mass per unit volume.
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Porosity
- Empty spaces between soil particles filled with air and water.
- Macro pores in spaces between aggregates
- Micro pores in spaces between particles of aggregates.
- Influences water infiltration and drainage.
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