Soils and the Environment A Summary of RI Envirothon Study Materials Compiled by Sally Paul
Why Soils Food and water resources Disposing of waste Support for human structures Growing timber and fibers Interact with forestry, wildlife, and water resources Bridgehampton Series, www.nesoil.com
RI Envirothon Soil Objectives Understand five soil forming factors Understand definitions of basic soil features and properties Recognize common landforms and parent materials Recognize the implications of soil features in the field Use knowledge of soils to make land use decisions Gain a working knowledge of the RI Soil Survey Understand and recognize erosion mechanisms and control practices
What will I be asked to do at the Envirothon? Answer questions about definitions and concepts (often multiple choice) Use the Soil Survey of Rhode Island to draw conclusions about a land area- map scale, symbology, soil series description and land use interpretations Evaluate a soil pit and surrounding landscape
Definition of Soil Depends on field or intended use Consists of minerals, organics, water, air Supports plants or shows evidence of pedogenesis Consists of naturally formed bodies Limited by rock/ice and deep water horizontally Upper limit air/shallow water Lower limit where biological activity stops/rock/2 m
Soil Profile Vertical cross-section of soil layers (horizons) Horizons differ in color, texture, structure, etc Common sequence in RI: O, A (E), B, C Birchwood Series, www.nesoil.com
Horizons O: formed from organic matter (plants and animals), commonly seen in forested areas but often absent in developed/cultivated areas Oa- highly decomposed Oi- undecomposed/fibric A: topsoil, mineral with lots of organics (making color darker), biologically active (roots, fungi, bacteria, mammals, bugs, worms, etc), most affected by acid rain Ap horizon- plow/disturbed layer, mixed O, A, E, B horizons. Thicker than A horizon (>2 inches) E: Eluvial horizon, zone of leaching, light in color, rare in RI due to cultivation
Horizons B: Subsoil, yellowish or reddish brown in well drained soils, accumulation zone (illuviation) C: Under the solum (A and B), less biological activity, weathering, structure, but still more weathered than bedrock R: Bedrock- RI soils are not formed in weathered bedrock as in many other areas (we will get to glaciation later)
Soil Forming Processes Additions - OM Removals - leaching out of soil completely Transfers - leaching to another part of profile Trasformations - biological and chemical reactions Weathering - mechanical or chemical OM breakdown Translocation up and down soil profile Accumulation
Soil Forming Processes Deeply weathered arid soil, Gene Dayton, Central Qeensland Universtiy Climate Precipitation, temperature, humidity, seasonal variability Direct effects: temperature and precipitation weathering Indirect effects: vegetation
Soil Forming Processes www.actagro.com/php/organics.php Living Organisms Vegetation most important, depends on climate, parent material, topography, drainage, etc. Microorganismsdecompose OM to provide nutrients, aggregation, water holding capacity
Soil Forming Processes Receding glacier in Iceland, NASA Parent Material (RI) Till: Mixed unsorted (unstratified) particle sizes laid down below ice Outwash: stratified sands and gravels carried by glacial water, flat areas Loess: wind-blown siltsized materials deposited over till and outwash Peat and Muck: organic, poorly drained soils
Soil Forming Processes Topography Shape of land s surfaceaffects parent material distribution, vegetation Soils on steep slopes tend to be thinner Slope and aspect Most important influence: water movement across landscape Colluvium, Lechworth State Park, NY 2007
Soil Forming Processes Time RI soils are young/weakly developed Wisconsonian glacier retreated in RI ~15,000 years ago Mature soils have maximum horizonation and are stable/ in equilibrium with environment Mature rainforest soil, Michael Ritter, Ph.D.
Soil Color Organic matter often gives soil a dark or black color Iron oxides give red/yellow/brown colors Gleyed soils are gray in color due to wetness, which depletes iron oxides Munsell Color System The Regional Institute Ltd.
Redoximorphic features (RMF s) www.nesoil.com Occur in wet (hydric) soils Fe is reduced in wet conditions, making it mobile in solution with soil water In dry times, the Fe may oxidize (think rust) to create brown/red mottles
Texture: the mineral fraction Sand- will not hold a ball in hand Loamy sand- will hold a ball in hand, won t ribbon Sandy loam- ribbons, gritty texture Silt loam- ribbons well, smooth texture, silt is floury when dry Fine sandy loam- ribbons, easily mistaken for silt loam, but less soapy/slippery in hand Gravel- >2 mm, pebbles * Note that sand particles can be seen with the naked eye, silt cannot
Why is texture important? Many people argue that texture is the most important soil characteristic Influences infiltration and percolation, water holding capacity, vegetation, buildability (i.e. shrink swell clays) Gives important clues to parent material when you are in the pit silty textures- loess sorted sands and gravels- outwash poorly sorted boulders to silt sized-till
Soil Structure http://cru.cahe.wsu.edu/cepublications/eb1633/fig3.gif Definition- grouping of soil particles into peds We look for shape in shovel in RI because our young soils all have weak structure Structure forms when clay, OM, and Fe oxides bind soil particles together
Consistence Definition- resistance of peds to damage Loose: pile of sand, no peds Friable: pop a ped, good for farming Firm: need two hands to break a ped, not common in RI unless you are in a Cd (dense till) http://www.sciencebuddies.org
Soil and Water Drainage: how fast excess water is removed based on slope, texture, and vegetation Runoff: how much surface water flows over surface- primarily based on slope Permeability: infiltration rate- how fast water flows through- depends on texture, structure, density, compaction
Excessively drained- coarse Somewhat excessively drained- sandy Soil Drainage Classes Well drained soils- finer, drain readily Moderately well drained- any texture w/ RMF w/in 18-36 Somewhat poorly drained- RMF w/in 8-18 Poorly drained- often wet to surface Very poorly drained- wet to surface and thick organic layer
Available Water Capacity (AWC) Definition- water is soil available to plants: AWC = FC - WP Field capacity (FC)- water held in soil against gravity (after it drains) Wilting Point (WP)- water held tightly in soil so plants can t use it Sandy soils- low AWC Clay soils- medium AWC Silty soils- highest AWC
Soil Reaction http://www.planetnatural.com/planetnatural/images/soil-ph.jpg ph: 0-14, 7 neutral In RI soils acidic due to: Granite parent material Leaching of bases Plants give off H + RI soils very strongly acid ph 4.5-5.0 ph often increased for agriculture by liming (CaCO 3 )
Cation exchange capacity (CEC) Buffer capactiy- ability to hold nutrients for plant use Clays and OM have highest CEC Little clay in RI- OM very important for soil fertility http://www.okstate.edu/artsci/botany/bisc3034/lnotes/micelle.jpg
End of Soil Basics!