Podcast
Questions and Answers
What is the water-holding capacity of sand compared to clay?
What is the water-holding capacity of sand compared to clay?
Which soil type has poor aeration?
Which soil type has poor aeration?
What is the ability of clay to store plant nutrients?
What is the ability of clay to store plant nutrients?
How does the shrink/swell characteristic of clay affect buildings, roads, and walls?
How does the shrink/swell characteristic of clay affect buildings, roads, and walls?
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Which soil type has the highest resistance to pH change?
Which soil type has the highest resistance to pH change?
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What is the generalization about the pollutant leaching potential of clay soil?
What is the generalization about the pollutant leaching potential of clay soil?
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What type of peds are column-like with rounded caps and are bounded laterally by other peds?
What type of peds are column-like with rounded caps and are bounded laterally by other peds?
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Which type of soil structure is often associated with very fine-textured soils?
Which type of soil structure is often associated with very fine-textured soils?
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Which practice increases the decomposition of soil organic matter and breaks up aggregates?
Which practice increases the decomposition of soil organic matter and breaks up aggregates?
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Which diameter range corresponds to 'Fine' size in soil particles?
Which diameter range corresponds to 'Fine' size in soil particles?
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What type of crops can help stabilize soil aggregates and improve soil structure according to the text?
What type of crops can help stabilize soil aggregates and improve soil structure according to the text?
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In soil science, what term is used to describe peds that show little or no tendency to break apart under light pressure?
In soil science, what term is used to describe peds that show little or no tendency to break apart under light pressure?
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What can create crusts that close pores and pathways for water and seedlings?
What can create crusts that close pores and pathways for water and seedlings?
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Which ions generally promote aggregation in soil?
Which ions generally promote aggregation in soil?
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What tends to have greater aggregate stability in soils?
What tends to have greater aggregate stability in soils?
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Which factor is NOT mentioned as influencing the stability of aggregates?
Which factor is NOT mentioned as influencing the stability of aggregates?
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What can shift and crack the soil mass, creating or breaking apart aggregates?
What can shift and crack the soil mass, creating or breaking apart aggregates?
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Which type of microorganisms binds soil particles together more effectively than bacteria?
Which type of microorganisms binds soil particles together more effectively than bacteria?
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What is the structure of graphite?
What is the structure of graphite?
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Which clay mineral is dominant in highly weathered soils?
Which clay mineral is dominant in highly weathered soils?
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Which type of clay mineral shrinks when dry and swells when wet?
Which type of clay mineral shrinks when dry and swells when wet?
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What is the main characteristic of illite clay?
What is the main characteristic of illite clay?
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Which mineral has an additional magnesium hydroxide sheet in its structure?
Which mineral has an additional magnesium hydroxide sheet in its structure?
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What is the distinguishing feature of amorphous silicate clays?
What is the distinguishing feature of amorphous silicate clays?
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What does CEC stand for in the context of soils?
What does CEC stand for in the context of soils?
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Why do sandy soils generally have lower CEC than clay soils?
Why do sandy soils generally have lower CEC than clay soils?
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Which soil texture category has the highest typical CEC value?
Which soil texture category has the highest typical CEC value?
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How does the organic matter content affect the CEC of the soil?
How does the organic matter content affect the CEC of the soil?
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What is a key factor that determines the magnitude of CEC in soils?
What is a key factor that determines the magnitude of CEC in soils?
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In terms of nutrient retention capacity, what does a high CEC indicate?
In terms of nutrient retention capacity, what does a high CEC indicate?
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Study Notes
Soil Aggregates and Structure
- Breakdown of aggregates creates crusts that close pores and other pathways for water and seedlings
- Optimum conditions for aggregates: large range of pore size distribution, large pores between aggregates, and small pores within aggregates
- Pore space provides zones of weakness through which plant roots can grow
Factors Affecting Aggregate Stability
- Soil texture and type of clay
- Extractable iron and cations
- Amount and type of organic matter (OM)
- Type and size of microbial population
- Expansion and contraction of clay particles can shift and crack the soil mass, creating or breaking apart aggregates
- Ca ions associated with clay generally promote aggregation, while Na ions promote dispersion
- Soils with > 5% iron oxides tend to have greater aggregate stability
- Soils with high OM content have greater aggregate stability
- Additions of OM increase aggregate stability after decomposition begins and microorganisms have produced chemical breakdown products/mycelia have formed
Soil Microorganisms and Aggregates
- Soil microorganisms produce organic compounds that help hold aggregates together
- Type and species of microorganisms are important
- Fungal mycelial growth binds soil particles together more effectively than bacteria
- Aggregate stability declines rapidly in soil under intensive cultivation
Classification of Soil Structure
- Classification of soil structure considers the grade, type, and size of peds
- Grade describes the distinctiveness of the peds
- Units are distinctly longer vertically (columnar), single grain (particles show little or no tendency to adhere to other particles), massive (show little or no tendency to break apart under light pressure), or have angular and subangular blocky, granular and crumb, platy, or prismatic and columnar shapes
- Size of peds varies from very fine (< 5 mm) to very coarse (> 50 mm)
Improving Soil Structure
- Organic matter management: regular additions feed the organisms that build soil structure
- Tillage practices: tillage increases decomposition of SOM and breaks up aggregates, but residues left at the surface protect aggregates from rain and encourage fungal growth
- Compaction prevention: compaction pushes aggregates together and eventually breaks them down
- Crops/cropping systems: dense roots of grasses, small grains, and pastures stabilize soil aggregates and improve structure
Cation Exchange Capacity (CEC)
- CEC is the measure of how many negatively-charged sites are available in the soil
- CEC determines the soil's fertility, nutrient retention capacity, and capacity to protect groundwater from cation contamination
- Soil properties that determine CEC are texture, clay mineral type, and OM content
- Sandy soils generally have lower CEC than clay soils
- CEC values vary by soil texture, with clay and clay loams having higher CEC than sands and loams
Clay Minerals
- Clay particles are colloids with large surface areas, high water-holding capacities, and slow movement of water and air
- Shrinking and swelling of clay particles affect buildings, roads, and walls
- Chemical adsorption is large in clay minerals
- Generalized influence of soil separates on soil properties and behavior
- Crystalline silicate clays have various types, including kandites, smectites, vermiculite, illite, and chlorite
- Each type of clay mineral has distinct properties and characteristics
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Description
Learn about the characteristics of clay soil, including its high plant nutrient content, small particle size, high water holding capacity, and unique plasticity. Explore how clay soil differs from sand and its ability to retain water and nutrients effectively.
