soils exam 4

the wearing away of the land surface by water, wind, or other natural or anthropogenic agents that detach the soil from one point on the earth's surface and deposit it elsewhere

• Detachment 
• Transportation of sediments
• Deposition

• loss of fertile topsoil 
• exposure of unproductive subsoil

• siltation of damns, lakes, river, etc.
• water pollution

• Natural: erosion under natural environmental conditions
• Accelerated: erosion that is much more rapid than usual

• Splash
• Sheet
• Rill
• Gully
• Steam erosion

• the particles are detached by the force of falling raindrops
• soil rises into the air and maybe moved by gravity or wind or water down-slope

soil particles are detached and transported in a thin layer or sheet by water flowing on surface

rills and gullies (gullies being larger) can be cut as runoff is allowed to concentrate and gain velocity

erosion that occurs along the banks of streams; cuts away at banks

• Surface Cover (vegetation) 
• Topography
• Soil Properties (texture, structure, aggregate formation, etc.)
• Climate Factors

• conservation tillage
• cover cropping
• mulching 
• proper timing of cultivation
• addition of soil conditioners (organic matter, lime)
• contour cultivation
• strip cropping

• no-till
• reduced till
• ridge till
• strip till
• mulch till

• Riprap
• Terracing
• Bioengineering
• Sediment traps
• Retention Ponds

• Large angular rocks may be laid at the bottom or side of channels where high water velocities may be expected
• stream bank erosion can account for 40% or more of total soil loss in some watersheds.

not very common in the US because we have cultivated lands that are relatively flat.

use of vegetaion to protect channels, reduce runoff velocity, and trap sediments

designed to slow down runoff and trap sediments

ponds constructed down-slope of field which collects runoff and allows sediments to settle prior to movement of surface water off-site

• To plan for the best management of a soil resource
• to evaluate the consequences of alternative tillage practices/shift in management strategy 
• To determine compliance of environmental regulations

• WEPP: Water Erosion Precition Project.  
• Predicts how rainfall will impact a site
• can predict on-site and off-site effects

• USLE: Universal Soil Loss Equation (now revised) 
• relies on statistical relations between easily observed factors to soil erosion (rainfall erosivity, soil erodibility, etc)
• Advantage: can show management strategies can affect erosion
• cannot predict erosion for a specific year (only average year) or storm
• sheet and rill erosion

• Wind moves 40% of the soil transported by erosion in the U.S.
• Problem in 75 million acres of land in the U.S.
• Up to 29 Mg/ha of wind erosion-induced losses had been recorded in New Mexico

• wind velocity and turbulence 
• surface roughness
• soil properties

25 km/hr, 15 mi/hr

• Saltation (50-90% of soil movement)
• Suspension (less than 15% of total movement)
• Creep

• removes the most fertile portion of the soil
• obscures visibility and pollutes the air and water
• causes automobile accidents and fouls machinery 
• imperils animal and human health

• Maintain or increase the protective cover of plants
• conservation tillage to maintain aggregate stability and reduce disturbance- especially in arid areas
• installation of barriers/wind breaks (aka wind barriers, shelterbelts)
• keep surface layer moist and rough

• Infertile 
• Low in organic matter
• often acidic
• subject to severe erosion and surface run-off

• control soil erosion: use fast-growing perennial vegetation 
• enrich soil organic matter: increases fertility and improves soil physical properties 
• correct soil pH
• conservation tillage 
• plant cash crops that cover the soil and employ crop rotation
• apply fertilizers

soils that are potentially extremely acidic (<3.5) because of the presence of large amounts of reduced form of sulfate that are oxidized to sulfuric acid if the soil is exposed to oxygen when they are drained or excavated.

• Continuous supply of organic residues (increase decomp rate)
• keep the soil vegetated 
• maintain soil fertility
• tillage should be eliminated or limited
• perennial vegetation (especially in natural ecosystems) should be encouraged

natural attenuation

• Sewage effluent: released into rivers/creeks OR applied as irrigation to crops OR surface-applied to drain-fields 
• Sludge: surface-applied to agricultural areas

• manure application rates based on N (P may be over applied inadvertently)
• Farmer apply extra to apply "enough"
• N and P may come from septic and domestic waste

• farm wastes (liquid wastewater and manure) 
• faculty septic systems
• domestic animals, stray animals and migratory birds
• contaminated irrigation and groundwater to wash produce

• high specific surface (lots of clay)
• Red soils- high iron content bacteria sorbs into/forms complexes with iron oxides
• well-drained soil/unsaturated soils (most pathogens are facultative anaerobes and will be out competed by aerobic microbes in oxygen-rich environments)

• mining
• manufacturing
• the use of synthetic products

• toxicity due to extended exposure (due to food chain transfer)
• some metals carcinogens
• acute poising through ingestion (rare)

you lower the pH

• if chromium, add organic matter
• if other heavy metals, drain soils for greater oxygen availability (creates oxides which are less soluble)