Soils – Nebraska’s Envirothon William C. (Chuck) Markley Resource Soil Scientist – North...
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Transcript of Soils – Nebraska’s Envirothon William C. (Chuck) Markley Resource Soil Scientist – North...
Soils – Nebraska’s Envirothon
William C. (Chuck) Markley Resource Soil Scientist –
North Platte, NE
Soil =
• Sand: That mineral part of a soil that you can feel as “gritty”
• Silt: That mineral part of a soil that is powdery when dry and slick when wet
• Clay: That mineral part of a soil too small to be seen without a microscope, but gives the soil a sticky feel—when wet; and to become brick hard when dry.
+• Organic Matter: The non-mineral part of a soil that
gives it dark color, aggregate strength and fertility
Physical Properties
• Texture: Percent of sand, silt and clay. (see textural triangle to make a list of textures)
• Structure: The form or shape of the individual soil aggregates or “peds” –this property is directly related to the aging process within the profile
• Aggregation: Created by the weathering process, pedoturbation by roots, insects & freeze-thaw; & from coatings from organic matter decomposition
• Consistence: Resistance of aggregates to rupture from applied stress & degree of cohesion/ adhesion
• Bulk Density: How tightly the soil particles are packed together (Increased B.D. slows H2O percolation)
• Soil Color: Shades of tan, brown, black, white, gray, red, or blue(green)
• Available Water Capacity: Total field capacity (saturation) minus non-available high-tension water held by the soil particles (sands—least AWC; silt loams—greatest AWC)
Structure
Consistence
Loose, blowing fine sand (lost during a single wind storm)
This was a germinated field of wheat! This guy lost some soil and some wheat because he didn’t understand soil consistence, but a neighbor’s field a few miles away caused a major crash on I-80 during this same storm: People died!
Soil Properties—Bulk Density
• Things that increase Soil Bulk Density:
• Tillage (disking/plowing): a dense pan forms underneath the coulters and shears after repeated tillage operations
• Wheel/hoof/pedestrian traffic: the weight of traffic over the soil can compress or completely crush the soil aggregates to a depth of as much as 24 inches (combines/grain carts)
• Natural Settling: following a disturbance (loss of excessive macro-pores)
• Liquid Compaction: used in building dams—can obtain up to 95% compaction in conjunction with mechanical compaction
• Any time soil is disturbed (whatever it is) when very moist or wet. (Dry soil is much less susceptible to compaction.)
Soil Properties—Color • Tans: Normal color of fresh parent material in most Nebraska soils
[exceptions: sandstones and shales]
• Dark browns: Surface color of grassland soils: (humic acids from decomposed O.M. cause the darkening of surface soils)
• Black: Wet soils, (usually high in O.M. like on floodplains)
• White: Washed Quartzitic sands; very high calcium carbonates and/or bicarbonate of soda coat soil peds with whitish coatings
• Gray: Wetness (also parent material color—shales); high calcium + wetness
• Red: Oxidized iron (rust stains) from intermittent reduction and saturation; (also parent material color—sandstones)
• Blue, Blue-green: Prolonged inundation/saturation—iron and other metals are reduced producing the blue or blue-green color
Soil Properties—Aggregation
• Crop Residues Organic matter humus humic acids
• Coatings of exudates -- larger aggregates• Fungal hyphae -- large weak aggregates• Root massing -- large weak aggregates• Humic acids -- electrically bonded to clay
micelles – small, very strong aggregates
Soil Profile• A Horizon: Surface horizon—every soil has an A
horizon, which is usually darker than other horizons from additions of organic matter, (except fresh sediments on a floodplain or foot-slopes may be light colored). It has granular structure.
• B Horizon: This horizon forms in older soils where clay has illuviated (trickled down) into this horizon from above. It has sub-angular blocky and prismatic structure.
• C Horizon: This is the parent material. Little or no structural development has occurred (massive or single-grain). A 2C horizon occurs where there has been a lithological discontinuity (or depositional change). Every soil has a C horizon at some depth.
• CR or R Contact: This is the depth (w/in rooting zone) at which bedrock or sedimentary rock is contacted. Root penetration is stopped.
Soil Landscapes
• Upland: Nebraska’s uplands may have formed in residuum (bedrock derived), glacial till, outwash, loess (wind-blown deposits) or very old alluvium
• Sandhills: These are wind-blown sediments that have dune and interdune topography. The sand was saltated (rolled, bounced) into place rather than carried aloft by wind.
• Tableland: This landscape differs from uplands primarily in its broad, relatively low relief across the entire interfluve (between river & stream valleys)
• River Valley: Caused by down-cutting of rivers and streams. Typically have a flood plain and terrace(s).
Southwest Nebraska Upland – Frontier County
Another Upland landscape in Frontier County
Sandhills landscape – McPherson County
Overgrazed corner—Logan County
Tablelands landscape – Perkins County
Valley landscape – Lincoln, Co.
Valley landscape – Lincoln County
Marsh –very poor drainageWetland—very poor drainage Wet-Subirrigated – poorly drained
Subirrigated – somewhat poorly drainedSandy lowland—mod. well drained
.
Tablelands
Uplands
Sandhills Tablelands
Sandhills
Public Land Survey
Public Land Survey
Hydric Soils
• From ‘hydra’ – “water” or wet soils• Are saturated, flooded or ponded (anaerobic
conditions) within the surface 12 inches for significant periods during the growing season
• Have redoximorphic concentrations (rust spots [metals oxidized] within the matrix, on ped surfaces, or along root channels, or
• Are gleyed (gray, blue or bluegreen) [metals reduced] throughout the matrix
• Can support & favor the dominance of hydrophitic vegetation
Redoximorphic Concentrations
Root Channel (end)
Surface of “peds”
Root Channel (side)
Erosion and Sedimentation
• Erosion: The loss of fertile, well aggregated surface soils by wind or water removal
• Sedimentation: The accumulation (deposition) of fertile and non-fertile sediments of structureless soil by wind or water agents
Sheet
Rill
Gully Erosion
Sheet and Rill
Rills
Erosion
Sedimentation
2004 Dust Storm – Kansas (Wind Erosion)