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Soils: facts and fiction

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1 Soils: facts and fiction
Note series for Environmental Science ENVI 152

2 Soil Definition (NRCS)
Soil is a natural body comprised of solids (minerals and organic matter), liquid, and gases that occurs on the land surface, occupies space, and is characterized by one or both of the following: horizons, or layers, that are distinguishable from the initial material as a result of additions, losses, transfers, and transformations of energy and matter or the ability to support rooted plants in a natural environment.

3 Downer soils are used mostly as woodland. The natural
vegetation consists of mixed oaks, hickory, and scattered pines. Downer soils occur on 291,319 acres in New Jersey. These soils are dominantly in the 11 counties of southern New Jersey. Downer soils are on uplands and formed in sandy, Northern Atlantic Coastal Plain deposits. The Downer series was established in the 1960’s in Gloucester County.

4 Soil Loss The loss of soils through erosion is a major problem
The loss of soil washes out potential nutrients that would be available The loss of soil nutrients will negatively impact plant diversity The loss of soil is becoming a greater problem today than in the past

5 Why Soil Loss? Development Clearing of fields for agriculture
Strip mining Natural weathering Edge effect Sea Level Rise

6 Soil types Soils are weathered rocks that create smaller particles
Classified as Sand, Silt or Clay Depending on the location, there are greater compositions of soil types (i.e. New Jersey coastal area has mostly sand, there clay soils in N. New Jersey

7 Soil Contamination Since soils are in the LITHOSPHERE (Crust), they will be exposed to more environmental stresses which will inevitably permeate down the soils possibly toward groundwater. Acid rain is a problem in that it displaces cations in the soil and causes changes in soil chemical compositions and pH

8 Soil Texture = %Sand, Silt & Clay in a soil.
Soil texture is the single most important physical property of the soil. Knowing the soil texture alone will provide information about: 1) water flow potential, 2) water holding capacity, 3) fertility potential, 4) suitability for many urban uses like bearing capacity

9 Particle Diameter Size
Soil particle diameters range over 6 orders of magnitude 2 m boulders Coarse fragments > 2 mm Sand < 2 mm to 0.05 mm Silt < 0.05 mm to mm Clay < m

10 Coarse Fragment > 2 mm Gravels, cobbles, boulders
Not considered part of fine earth fraction (soil texture refers only to the fine earth fraction or sand, silt & clay) Boulders left in valley of Big Horn Mts.(Wy) by a glacier.

11 Sand < 2 mm to > 0.05 mm Visible without microscope
Rounded or angular in shape Sand grains usually quartz if sand looks white or many minerals if sand looks brown, Some sands in soil will be brown, yellow, or red because of Fe and/or Al oxide coatings.

12 Sand Feels gritty Considered non-cohesive – does not stick together in a mass unless it is very wet.

13 Sand Low specific surface area
Sand has less nutrients for plants than smaller particles Voids between sand particles promote free drainage and entry of air Holds little water and prone to drought

14 Silt < 0.05 mm to > 0.002 mm Not visible without microscope
Quartz often dominant mineral in silt since other minerals have weathered away.

15 Silt Does not feel gritty Floury feel –smooth like silly putty
Wet silt does not exhibit stickiness / plasticity / malleability

16 Silt Smaller size allows rapid weathering of non quartz minerals
Smaller particles – retains more water for plants and have slower drainage than sand. Easily washed away by flowing water – highly erosive. Holds more plant nutrients than sand.

17 Source of Silt

18 Wet clay is very sticky and is plastic or it can be molded readily into a shape or rod.
Easily formed into long ribbons Shrink swell – none to considerable depending on the kind of clay. Clay

19 Clay Pores spaces are very small and convoluted Water holding capacity
Movement of water and air very slow Water holding capacity Tremendous capacity to adsorb water- not all available for plants. Soil strength- shrink/swell affects buildings, roads and walls. Chemical adsorption is large

20 USDA Textural Classes Sandy soils (coarse) Loamy soils (medium)
Fine sand Very fine sand Loamy soils (medium) Clayey soils (fine)

21 Textural Triangle

22 Sandy Soils Coarse texture Sands Loamy sands

23 Changes in soil texture
Over long periods (1000s yrs) pedologic processes alter soil horizon textures. As soils get older sand weathers to silt and silt weathers to clay….therefore old soils have more clay.

24 Determining Soil Texture - Feel Method
Wet soil in hand Make ribbon Length of ribbon indicates clay content Grit or lack of grit indicates sand or silt Smoothness indicates silt

25 Naming Soil Horizons Soil horizons (layers in the soil) are named so differences between soils can be identified. Naming soil horizons takes practice

26 Organic Horizons O - horizon - organic material (no mineral materials) ) forest litter ) organic soil or peat soils, or muck

27 Organic Soil Profile This trenching machine is digging through the Oe
horizon of an organic soil. Trenches needed to remove water so the peat will dry before harvest.

28 Mineral Soil Horizons A horizon - surface horizons that accumulate A B
B (t) B (C) C

29 <--What causes the layers?

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