Soils We know more about the movement of celestial bodies than about the soil underfoot.- Leonardo da Vinci Soil: DefinitionSolid earth material that has been altered by physical chemical and or!anic processes so that it can support rooted plant life."n!ineerin! definition: #nythin! that can be removed without blastin! Soil $roduction Soil $roduction: %nputs&onversion of rock to soil Soil $roduction: 'utputsDownslope movement of soil Soil (hickness: Stora!eSoil thickness reflects the balance between rates of soil production and rates of downslope soil movement.SlopeWeatherin! )ate *actors of Soil *ormation&limate'r!anisms$arental +aterial(opo!raphy(ime *actors of Soil *ormation&limate(emperature and precipitation%ndirect controls ,e.!. types of plants-Weatherin! rates(he !reater the rainfall amount the more rapid the rate of both weatherin! and erosion. *actors of Soil *ormation'r!anisms(ypes of native ve!etationWeatherin! is dependent of plant !rowth$lant and animal activity produces humic acids that are powerful weatherin! a!ents.$lants can physically as well as chemically break down rocks.$lants stabili.e soil profiles #nimals ,includin! humans- tend to increase erosion. *actors of Soil *ormation$arent +aterial:&hemistry+ineralo!y /rain si.e *actors of Soil *ormation(opo!raphy:/round slope"levation#spect ,e.!. north facin! vs. south facin! slopes- Downslope transport of soil is a function of slope:

"rosion rate 0 f,S-(he steeper the surface slope the more likely any eroded material is to be transported out of the system.*actors of Soil *ormation Soils on hillslopes reach an e1uilibrium thickness often about 2 m.Soils on flat surfaces such as floodplains or plateaus tend to thicken throu!h time due to weatherin! rates bein! !reater than sediment transport rates.*actors of Soil *ormation *actors of Soil *ormation(imeDevelopment and destruction of soil profiles(ypical reaction rates are slow the lon!er a rock unit has been e3posed the more likely it is to be weathered. Soil Development %nputs from outside ecosystem4 #tmospheric inputs $recipitation dust deposition4 5ori.ontal inputs *loods tidal e3chan!e erosion land-water movement %nputs from within ecosystem4 Litterfall and root turnover#dditions to Soils Decomposition of or!anic matter 5umification to form comple3 or!anic matter Weatherin! of rocks4 $hysical weatherin! *ra!mentation of rock4 *ree.e-thaw6 dryin!-wettin!6 fire $hysical abrasion4 #brasion by !laciers4 &hemical weatherin! Dissolves primary minerals *orms secondary minerals(ransformations 7reakdown of soil or!anic matter to form soluble compounds that can be absorbed or leached Depends on 4 8uantity of input4 Location of input ,roots vs. leaves-4 "nvironment (emperature +oistureDecomposition Soil 5ori.ons Layers in Soil 9ot Deposited but :ones of &hemical #ctionSoil $rofile Suite of 5ori.ons at a /iven Locality Soil 5ori.ons and $rofiles Soil $rofiles'ver time different levels of a soil can differentiate into distinct hori.ons that create soil profiles.&hemical reactions and formation of secondary minerals ,clays-. Leachin! by infiltratin! water.Deposition and accumulation of material leached from hi!her levels in the soil. Soil $rofiles &ookport soil $ennsylvania& 5ori.on7 5ori.on# 5ori.on $hysical weatherin! breaks rocks into small mineral particles. &hemical weatherin! dissolves and chan!es minerals at the "arth;s surface. Decomposin! or!anic material from plants and animals mi3es with accumulated soil minerals. $arent material ,bedrock- under!oes weatherin! to become re!olith ,soil < saprolite-. Soil is a mi3ture of mineral and or!anic matter lackin! any inherited rock structure.Soil Saprolite is weathered rock that retains remnant rock structure. Saprolite Saprolite 7alance 7etween: Downward Lowerin! of /round Surface Downward +i!ration of Soil 5ori.ons %f erosion rapid or soil evolution slow soils may never mature beyond a certain point. "3tremely ancient soils may have lost everythin! movableLimits of Soil Development )ates of Soil Development=.S. Department of #!riculture estimates that it takes >?? years to form an inch of topsoil.(hat;s less than ?.?2 mm yr-2 "rosion of 9atural &apital+odern rates of soil loss are 2?? to 2??? times rates of soil formation ,typically mm yr-2 to cm yr -2 in a!ricultural settin!s-.Sets up a fundamental problem due to the erosion of natural capital@ Soil and the Life-&ycle of &ivili.ations5ow lon! would it take to erode 2 m thick soilA(hickness of soil divided by the difference between )ate of soil production and erosion. 2 mB 2??? years2mm - .?2 mm(his is about the life-span of most maCor civili.ations... +anDdespite his artistic pretensions his sophistication and his many accomplishmentsDowes his e3istence to a si3-inch layer of topsoil and the fact that it rains.- #uthor =nknown 9ational #rchives: 22E S& >?FG# nation that destroys its soils destroys itself. 4 $resident *ranklin D. )oosevelt *eb. HI 2GJK.