Soil Physical Properties

Transcription

1 Soil Physical Properties ESRM 311 SEFS 507 Some examples of mineral soil development eg, Rock Weathering Types of Weathering Physical/Mechanical Chemical Biological Photo by D Vogt CO 2 + H 2 O H 2 CO 3 air water carbonic acid CaCO 3 + H 2 CO 3 Ca(HCO 3 ) 2 limestone carbonic calcium acid bicarbonate Mineral soil development eg, Rock Weathering Organic matter Parent material Organic matter Mineral particles & organic matter Parent material Organic matter Mineral particles & organic matter Parent material A horizon A horizon B horizon Disintegrating rock C horizon C horizon C horizon Bedrock Bedrock Bedrock Bedrock Soil begins to form Simple organisms Layers called horizons A well developed soil and soil.html 3 1

2 Weathering s Physical Influence on Soil Directly Texture sand, silt, clay Structure Porosity Consistency Aeration Temperature Moisture Indirectly Bulk density Color 4 Soil Physical Properties Horizons Color Texture and Pores Structure Consistence Bulk Density 5 Weathering s Visual Influence on Soil: Soil Layers (Horizons) 6 2

3 Soil Color Depicts OM brown or black, moisture moist is darker, and parent material eg, if Fe: salts lighter,?? aerobic = red, or anaerobic = gray/blue Affects temperatures Indirectly, if OM, it affects nutrients, moisture, etc??? 7 7 Soil Color Red Yellow Purple Green Blue 88 Texture Soil texture refers to the proportion of the soil separates that make up the mineral component of soil (fine earth fraction < 2mm). These separates are called sand, silt, and clay. These soil separates have the following size ranges: Sand = <2 to 0.05 mm Silt = 0.05 to mm Clay = <0.002 mm % sand, silt and clay 9 3

4 Texture 10 Soil Pores 11 Soil Pores 12 4

5 Soil Pores 13 The soil separates can become aggregated together into discrete structural units called peds. These peds are organized into a repeating pattern that is referred to as soil structure. Between the peds are cracks called macropores through which soil air and water are conducted. Soil structure is most commonly described in terms of the shape of the individual peds that occur within a soil horizon. 14 Aggregate: Soil particles glued together with organics and/or clays and oxides. 15 5

6 Clayey aggregates Intraped micropores Macropores Coarse sand grains % 5 15% 18 6

7 poor structure 35 40% 5 15% 20 25% 25 30% 19 aggregates 20 Soil Consistence Soil consistence refers to the ease with which an individual ped can be crushed by the fingers. Soil consistence, and its description, depends on soil moisture content. 21 7

8 Soil Consistence Terms commonly used to describe consistence are: Moist soil: Wet soil: Dry Soil: loose noncoherent when dry or moist; does not hold together in a mass friable when moist, crushed easily under gentle pressure between thumb and forefinger and can be pressed together into a lump firm when moist crushed under moderate pressure between thumb and forefinger, but resistance is distinctly noticeable plastic when wet, readily deformed by moderate pressure but can be pressed into a lump; will form a wire when rolled between thumb and forefinger sticky when wet, adheres to other material and tends to stretch somewhat and pull apart rather than to pull free from other material soft when dry, breaks into powder or individual grains under very slight pressure hard when dry, moderately resistant to pressure; can be broken with difficulty between thumb and forefinger 22 Soil Bulk Density Bulk density is the proportion of the weight of a soil relative to its volume. It is expressed as a unit of weight per volume, and is commonly measured in units of grams per cubic centimeters (g/cc) or tons per cubic meter (Mg/m 3 ). Bulk density is an indicator of the amount of pore space available within individual soil horizons as well as compaction. 23 Soil Bulk Density common The average particle density of mineral soil material is 2.65 g/cc 24 8

9 Root structure belowground 25 Many counties in the U.S. have a Soil Survey produced by Natural Resources Conservation Service (NRCS) Soil Surveys Maps Profile descriptions Tables on soil properties: physical, chemical, engineering, land capabilities, plant growth 26 ALDERWOOD SERIES The Alderwood series consists of moderately deep to a cemented pan, moderately well drained soils formed in glacial till. Alderwood soils are on glacially modified foothills and valleys and have slopes of 0 to 65 percent. The average annual precipitation is about 40 inches, and the mean annual temperature is about 50 degrees F. TYPICAL PEDON: Ap--0 to 7 inches; very dark grayish brown; gravelly ashy sandy loam; moderate fine granular structure; slightly acid (ph 6.2). (3 to 7 inches thick). Roots? Bs1--7 to 21 inches; dark yellowish brown; very gravelly ashy sandy loam; weak medium subangular blocky structure; slightly acid (ph 6.2). Bs2--21 to 30 inches; dark brown; very gravelly ashy sandy loam; weak medium subangular blocky structure; slightly acid (ph 6.2). (Combined Bs1 and Bs2 horizons are 15 to 30 inches thick) 2Bs3--30 to 35 inches; 50% olive/yellowish brown and 50% dark greyish brown; very gravelly sandy loam, some cemented fragments, massive; moderately acid (ph 6.0). (0 to 15 inches thick) 2Bsm--35 to 43 inches; dark grayish brown cemented layer that crushes to very gravelly sandy loam; massive; 40 percent pebbles; moderately acid (ph 6.0). (5 to 20 inches thick) 2Cd--43 to 60 inches; grayish brown compact glacial till that breaks to very gravelly sandy loam; massive; extremely hard; 40 percent pebbles; moderately acid (ph 6.0). 27 9