Factors of Soil Formation Flashcards
What are PM weathering rates determined by?
Mineralogy, hardness, porosity, surface area(faster) or finer grains(water retention)
Solum
These are the surface and subsoil layers that have undergone same soil-forming conditions
Example of soil created by PM…
Quartz sand doesn’t create clay soils due to no Al
PM soil formation with igneous rocks…
Form abundant clay minerals with high fertility due to cations and building block
Example of materials determining weathering rates…
Granite contains mostly quartz and K feldspars, less quartz and more Na and Ca feldspars are mafic
What do sedimentary rocks depend on?
Formation fpressure, composiion of original deposit, sandstone orignates from sand-size sediment
Why are transported soils more productive?
Higher porosity
How does wind sort particles?
Drops largest particles newar source, carrying smaller larger distances
Loess
Terrestrial clastic sediment composed predominantly of silt-size particles formed by accumulation of wind-blown dust
Ice/Water particle distribution…
Glacial till and glaciations
Colluvium
This is soil and debris that accumulate at the base of a slope by mass wasting or sheet erosion
Climate variability in soil formation….
Precipitation/temperature most important, varying depending on elevation/latitude, yearly also
Cool humid climate soil characteristicis…
High OM accumulation, weathering products removal and dominant acidification
Arid-semiarid climate soil characteristics…
Evapotranspiration exceeds precipitation, OM accumulates more slowly, with rapid soluble salt and carbonate accumulation
What is regional climate characterised by?
Mean annual temperature and precipitation
Results of poor drainage or high water table?
Dominant redox reactions and gleying
Temperature influence on sois…
Increases clay formation, clay type then influenced by climate: smectite found in drier climates than kaolinite
Example of topgoraphy improtance?
Slope length and angle determine effective precipitation
How slope influences soil?
Soil development(pedon thickness and horizon differentation) decreases with slope with increasing erosion
How do slopes differ per hemisphere?
NH north faceing slopes colder due to less incident solar radiation
How do plants add OM?
Root exudates, ell death with root growth and death/degradation
How does OM influence soil formation?
Produce compounds that chelate cations and humus production
How does canopy interception influence soils?
Rainfall assimialtes dissolved ions in crown drip, reacting with soil solid phase differently than pure water
Hans Jenny equation?
S = f(Pm, C, R, B, T)
Example of climate and time syngerism…
Calcaerous rock with moderate rainfall may have increased OM early, approaching equilibrium in few decades, whilst calcite and lcay take longer for steady levels for vegeatation
Hydrolysis
H+ in H2O replacement, like clay mineral feldspar releasing K and adding H, accelearting weathering
What can released K ion replaced by H+ do?
Form new complexes, cationic exhcnage, plant use, soil leeching
What does hyrdolysis increase with?
OM decomposition, nutrient uptake, nitrification and S oxidation, as pH lowers with increasing H+
How does hydration differ from hyrdolysis?
Water does not dissociate, expanding minerals and increasing weathering susceptibility
Where are redox reactions most important?
Fe2 oxidation to Fe3 which strains crystals and accelerates weathering rate
How do redox reactions influence solubility?
Some cations more mobile when reduced than when oxidised
What are the two horizon groups?
Master Horizons - AOEBCR
Transitional Horizons
A Horizon
Surface layer with high bio-activity thus high humus accumulation, mineral weathering, soluble product leaching and eluviation
Eluviation
This is the sideways or downards movement of dissolved or suspended material within soil caused by rainfall
O Horizon
Predominanntly organic matter
E Horizons
Eluviation influenced by organic acid from A/O horizons combination with leaching waters that weather/translocate silicate clays, fe and al, leaving residual material
