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)