Weathered Rocks from the lithosphere are the parent materials for soils Nature of the parent material will greatly influence time it takes to make soil and the nature of the soil that is formed Types of Parent Material Residual Colluvial Water Ice Wind Organic material Colluvial debris: Rocks that have fallen down hills Residual:Parent material in place The Castelleia series (CO) consists of well drained soils formed in thick noncalcareous, stony medium to moderately fine materials weathered locally from quartz, latite, or similar rocks. Arawak series, US Virgin Islands The Arawak series consists of shallow, well drained, slowly permeable soils on summits and side slopes of limestone hills and mountains. They formed in material weathered from soft limestone bedrock. 1
Water:Alluvial deposits Sediment that is deposited by rivers Water:Alluvial deposits Sediment that is deposited by rivers Forkwood soil, Wyoming The Forkwood series consists of very deep, well drained soils formed in slopewash alluvium derived from interbedded shale and argillaceous sandstone. Water:Marine (sediments deposited by oceans) Pamunkey soil, Virginia Soils of the Pamunkey series are very deep and well drained. They formed in Piedmont and Coastal Plain sediments. 2
Water:Lacustrine (materials deposited by lakes) Glacial till: Material transported by glacial ice Pleistocene Epoch 2 million years Glacial till: Material transported by glacial ice Eolian: Materials transported by wind Loess Glaciers - Loess Summer Melt water from glaciers would carry fine particles or sediment Winter Water would dry out leaving dry sediment Winter winds would transport the sediment Loess - Illinois Peoria - 25,000-12,000 Roxanna - 60,000-26,000 3
Loess - China Lanzhou - 440,000 sq km 50-300 meters deep From Gobi desert Loess - Washington Paloose hills in eastern Washington Soil series Wallawalla Paloose Athena Eolian: Materials transported by wind Volcanic ash Organic:Wet areas where accumulation> decomposition Peat bogs (1)Parent materials + 4 other factors of soil formation Climate Topography Time Biota 4
We talked about rocks, rock weathering and parent materials How soil is formed Factors of soil formation Different scenarios For soil formation: Soil Science Taxonomy Soil as a natural body Each soil as a unique individual Developed as a result of the 5 factors of soil formation Regolith O A E B C Solum Regolithweathered rock and soil that overlays bedrock Solum - portion of the regolith that shows the development of layers called soil horizons Soil formation is, simultaneously Breakdown of old Synthesis of new Losses Additions Translocations X Y Bedrock (1)Parent materials + 4 other factors of soil formation Climate Topography Time Biota Climate Moisture Quantity Intensity distribution Temperature Can be interrelated and interact 5
Role of water Rainfall: Intensity and duration Essential for chemical weathering Transport materials through horizons Determine type of plant cover Effective precipitation Water has to go into the soil Infiltration - not overland flow Rainfall exceeds evaporation Rate of biological activity Rate of chemical reactions Temperature Soil Development Time Line Effect of Time Topography Same parent material, same climate Organic Matter Accumulation CaCO 3 Accumulation Structural Development Unweathered Loess CaSO 4 Accumulation Time Location, location, location 6
Excessively drained Well drained Toposequence Poorly drained Very poorly drained Biota - plants Type of plant : Grass Dense root system Above ground foliage will die annually Grows where moisture < trees Thick A horizon Soil Profile A - mollic horizon Tree - deciduous Leaves high in cations (Ca, Mg, Fe..) Annual leaf fall Well developed A horizon Decomposed OM High nutrients Deciduous - Larger A horizon More cations Less acidic More clay translocation 7
Tree - coniferous Leaves low in cations Little leaf fall Thin A horizon Oi - slightly decomposed E horizon eluviation Coniferous Acidic Thin A E (eluviation) Animals Pedoturbation Animal burrows effectively mix soil from different horizons Earthworms Soil mixing Soil structure Soil aeration Animals Animals Humans Agricultural practices Accelerate soil loss Accelerate soil formation Start with a pile of rocks Physical and chemical weathering Breakdown particles Change mineral structure 8
Plant starts growing Organic matter is added to soil surface Root exudates further break down minerals First stage of soil formation Increased organic matter in A horizon When a plant starts growing Organic matter from plants is a nutrient source for other organisms Next stage will involve development of a B horizon Cations that have been solubilized by plant exudates, microbial activity,and acidification will start moving lower into the soil Secondary clays have been formed in A and are also moving down the profile Beginning of a B horizon Dark A horizon Organic matter Clays Something below the A that looks different from the parent material Parent material 9