Soils Exam 2
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Which is static, texture or structure?
Texture is static, structure is dynamic
What are the top two coloring agents?
- (1) Organic matter (darkens soil)
- (2) FeO2 (red/orange/yellow)
Size of Silt
the amount of particle surface area exposed and available as a site for chemical and physical processes per unit mass or volume of soil
Specific surface affects:
- (1) Adsorption/retention of water
- (2) Adsorption of chemicals
- (3) Area for chemical reactions
- (4) Aggregation
- (5) Microbial colonization
Specific surface (As) is a function of which two things?
- (1) Particle size
- (2) Mineralogy
Characteristics of Coarse soils
Holds less water/nutrients, not very erosive, very permeable, may compact to form hardpan
Characteristics of fine soils
holds large amounts of water/nutrients, erosion, slow permeability, and may shrink/swell.
Structure is the arrangement of primary sand, silt, and clay particles into secondary aggregates called peds or structural units which have distinct shapes are easy to recognize.
Soil structure: structureless
Soil structure types
Granular, block, platy, columnar, prisimatic
Columnar vs prismatic
columnar is rounded on top, prismatic is flat on top
Soil structure grade
scale from 0-3 (0 being structureless)
What causes soil structure to develop?
- (1) wetting/drying
- (2) Plant activity and root pressure
- (3) Microorganisms
- (4) Cementing by clay, organic matter, iron and aluminum compounds
Management of soil structure involves
- (1) Minimizing soil disturbance
- (2) Timing disturbance
- (3) Add the proper amounts of lime and fertilizer (plant growth)
- (4) Maintain or increase organic matter contents of Ap horizon.
the breakdown of large, air-dry soil aggretates into smaller microaggregates when suddenly immersed in water.
Particle density (Dp)
Dp = mass of dry soil/soil solids - volume of soil solids
An index of compaction. Increased compaction, increased Db. Larger particle size, increased Db.
Db = mass of dry soil - bulk V of soil material
Db = mass soil solids - (V of soil solids + volume of pores)
What farm operation may cause compaction?
As bulk density increases...
- (1) Soils become more compact
- (2) Soil strength increases
- (3) pore space decreases
percent pore space; F*100
a soil physical property which indicates how much of the bulk volume of the soil is occupied by pores.
f = Vpores + Vtotal
- >0.08 in diameter
- Influenced by soil structure
- allow for mvt of ai and water
- normal field conditions contain air
Types of macropores
- (1) Interparticle
- (2) Tubular
- (3) Planar voids (cracks between peds)
- Influenced by soil texture
- <0.08 mm in diameter
- mesopores are included here
- tend to hold water
- less air in micropores
- less air mvt; water mvt slow
Soils with a high porosity can benefit upland crop culture due to:
- can accomodate a large V of air and water
- Air and water mvt may be effective
- Limited or no problem of root penetration
- Soil is relatively less prone to erosion
- describes the ease with which a soil can be reshaped or ruptured
- refers to the degree of plasticity and stickiness of the soil
- soil consistence is affected by the type and amount of clay in the soil (high clay content means high stickiness)
the capacity of a soil mass to withstand stress without rupturing or becoming deformed
An atterberg limit. Water content (%) beyond which the soil will transform into a malleable, plastic mass and cause additional swelling; never disturb soil when the moisture content is above the plastic limit
Water content (%) when water transforms into a viscous liquid that will flow when jarred
Coefficient of liner extensibility
quantifies the expansiveness of a soil
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