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
(5) Microbial colonization
Specific surface (As) is a function of which two things?
(1) Particle size
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?
(2) Plant activity and root pressure
(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
(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