Soils: facts and fictionNote series for Environmental Science ENVI 152

The Earth and Its LayersFrom the U. of Colorado

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. NRCS - Natural Resource Conservation Service

Downer soils (NJ State Soil)

Found in woodland areas with naturalvegetation consisting of mixed oaks, hickory, and scattered pines.

Occur on over 291,000 acres in NJ (in all 11 counties of southern/central NJ).Downer was established in the 1960s in Gloucester County.

Soil Loss Through erosion (major problem)

Washes out potential nutrients that would be available Lost nutrients will negatively impact plant diversity

Why Soil Loss?Development (Key factor)Clearing of fields for agriculture (LDCs)Strip mining (Global)Natural weathering (Forming soils)Edge effect (Related to Development)Sea Level Rise (Loss of Coastal Shoreline)

Soil types Soils are weathered rocks that create smaller particles Classified as Sand, Silt or ClayDepending 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

Soil ContaminationSince soils are in the LITHOSPHERE (Crust), they will be exposed to more environmental stresses. Acid rain is a problem in that it displaces cations in the soil and causes changes in soil chemical compositions and pH

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) Infiltration of water 2) Porosity 3) Nutrient holding ability

Textural Triangle

Particle Diameter SizeSoil particle diameters range over 6 orders of magnitude2 m boulders Coarse fragments > 2 mmSand < 2 mm to 0.05 mmSilt < 0.05 mm to 0.002 mmClay < 0.002 m

Coarse Fragment

> 2 mm Gravels, cobbles, boulders Not considered part of fine earth fraction Boulders left in valley of Big Horn Mts.(Wy) by a glacier.

Sand< 2 mm to > 0.05 mm

Visible without microscope

Rounded or angular in shape

Can contain quartz or calcium carbonate & sometimes minerals

Feels Gritty

SandLow specific surface areaSand has less nutrients for plants than smaller particlesVoids between sand particles promote free drainage and entry of airHolds little water and prone to drought

Silt

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

Silt

Does not feel grittyFloury feel smooth like silly puttyWet silt does not exhibit stickiness / plasticity / malleability

SiltSmaller 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.

Source of Silt

Clay

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

ClayPores spaces are very small and convoluted Movement of water and air very slowWater 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

Determining Soil Texture - Feel MethodWet soil in handMake ribbonLength of ribbon indicates clay contentGrit or lack of grit indicates sand or siltSmoothness indicates silt

USDA Textural Classes

Sandy soils (coarse)Fine sandVery fine sand

Loamy soils (medium)

Clayey soils (fine)

Sandy SoilsCoarse textureSandsLoamy sands

Changes in soil textureOver 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.

Soil Horizons

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

Organic HorizonsO - horizon - organic material (no mineral materials) 1) forest litter 2) organic soil or peat soils, or muck

Organic Soil Profile

This trenchingmachine is diggingthrough the Oe horizon of an organic soil.

Trenches needed to remove water so thepeat will dry beforeharvest.

Mineral Soil HorizonsA horizon - surface horizons that accumulate

B horizon usually iron and leached minerals locally

C horizon more rock and parent material

A B B (t) B (C)C

Photo Courtesy of Paul Pete McLain

SoilMoisture Soil Conductivity Nest Gases NestTemperature SoilCompositionNest MicrohabitatNest Microhabitat Factors

Desiccated Eggs

New dredge 66.0% (n=33).

Partially washed dredge 32.7% (n=16).

Fully washed dredge 16.7% (n=8).

Reference nests 9.7% (n=14) .

2008 Nest Carbon Dioxide Content (%) at North Sedge Island: A Comparison Between New Dredge and Sand Treatments Over the Second 30 Days of Incubation

So How Important Are Soils?