Understanding Soil Formation Cover of N.C. Agric. Res. Bull. 467 Understanding Soil Formation

Mendocino Staircase Hans Jenny (1899 - 1992)

http://static.panoramio.com/photos/original/1006030.jpg

The Hans Jenny Pygmy Forest Reserve Extremely acid and infertile In this complex “ecological staircase,” each terrace is ~ 100,000 years older than the one below it and supports a distinct association of soils, plants, animals and microbes. Pygmy forest . Giant trees The highest and oldest of five wave-cut terraces that rise from the chilly waters of the Pacific Ocean. Extremely acid and infertile soil Beach sand

How is it possible that soil can naturally become so unproductive?

Where is Macomb in this sequence? Dr. Jenny also studied climosequences across the Great Plains. Brady and Weil, 2002

5 factors of soil formation Soil = f (Cl, O, R, P, T…) H Jenny refined the ideas of Russian scientist VV Dokuchaev into the following equation: Relief Time Climate 5 factors of soil formation Organisms Parent material

Young Soils Older Soils Which factor is most important ??? Organisms Climate Which factor is most important ??? Young Soils Older Soils Parent material Topography

Many of these deposits are hundreds of feet thick! Understanding parent materials in Illinois Glacial deposits cover most of Illinois Many of these deposits are hundreds of feet thick!

Retreating Glacier

silt sized glacial flour, transported by wind, Depth of loess cap LOESS silt sized glacial flour, transported by wind, deposited near rivers

secondary clay minerals Glaciation Primary minerals chemical weathering physical weathering dissolution chemical weathering alteration precipitation K+ HCO3- Ca+2 Cl- SO4-2 Na+ sand and silt ions in solution leaching secondary clay minerals

Increasing temperature Climatic variation Increasing rainfall Increasing temperature RR Weil

NO ! Average annual precipitation in IL 1951-1990 Have precipitation levels remained constant during the last 10,000 years ? NO !

Topographic variation N.C. Agric. Res. Bull. 467 Topographic variation Poorly drained Interstream divide Somewhat poorly drained Moderately well drained LANDSCAPE POSITIONS Well drained Poorly drained Shoulder Common in IL Valley floor SOIL DRAINAGE CLASSES Backslope

Soil Associations in McDonough County, IL Topography of McDonough County, IL 800 feet above sea level A soil association is a group of soils that are found together in a landscape 470 feet above sea level

Vegetative variation Grassland Forest Organic- rich A horizon From Brady and Weil, 2002

How much of Illinois was originally covered by tall grass prairie ? How much of Illinois was originally covered by forest ? 13.8 million acres 22 million acres Corn and soybean dominate IL landscapes today but we know where the prairie and forest use to be because of the soils Illinois once was covered by a complex mix of prairie and forest Prairie dominated the flat expanses Forest dominated the hilly land Old growth forest in

Temporal variation Lake terrace chronosequence in northeastern Michigan http://soils.umn.edu/academics/classes/soil2125/doc/s4chp4.htm

Young Soil in NC Old Soil in NC Poorly Defined Horizons Low Degree of Weathering Slightly Leached Thin Solum Well Defined Horizons High Degree of Weathering Highly Leached Thick Solum http://www.mo15.nrcs.usda.gov/features/gallery/

Adapted from Stewart (1990) Precipitation plus solutes, aerosols and particulates Additions Additions Sediment Loss of gases N2, N2O, CO2 Losses Soil forming processes Sediment Losses Capillary rise of dissolved ions E(i)lluviation of clay CaCO3 dissolved ions dissolved OM Organic residues  humus Primary  Secondary minerals minerals TRANSLOCATIONS TRANSFORMATIONS TRANSLOCATIONS Capillary rise of salts Additions Leaching of dissolved ions & OM Losses Adapted from Stewart (1990)

Water driven translocations Illuviation Eluviation Illuviation Illuviation http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/soil_systems/soil_development_profiles.html

Typical Florida flatwoods soil E uviation = depletion l I uviation = accumulation ll http://www.fnps.org/photos/spodosol.jpg

Conceptual chronosequence http://courses.soil.ncsu.edu/resources/soil_classification_genesis/soil_formation/soil_transform.swf

Chronosequence in California Foth, 8th ed.

Characteristics that differentiate soil horizons Color Texture Density Structure Organic Matter content Acidity Mineral Accumulations Biological activity RR Weil

Soil horizons Master Soil Horizons Most Weathered Least weathered RR Weil