Presentation on theme: "Soils – Nebraska’s Envirothon William C. (Chuck) Markley Resource Soil Scientist – North Platte, NE."— Presentation transcript:
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)
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).
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
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