Soils: facts and fiction

Note series for Environmental Science Note series for Environmental Science

ENVI 152 ENVI 152

Soil Definition (NRCS)

““Soil is a natural body comprised of solids Soil is a natural body comprised of solids (minerals and organic matter), liquid, and gases (minerals and organic matter), liquid, and gases that occurs on the land surface, occupies space, that occurs on the land surface, occupies space, and is characterized by one or both of the and is characterized by one or both of the following: horizons, or layers, that are following: horizons, or layers, that are distinguishable from the initial material as a result distinguishable from the initial material as a result of additions, losses, transfers, and transformations of additions, losses, transfers, and transformations of energy and matter or the ability to support of energy and matter or the ability to support rooted plants in a natural environment.” 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 all11 counties of southern/central NJ).Downer was established in the 1960’s in Gloucester County.

Soil Loss

Through erosion (major problem)Through erosion (major problem)

Washes out potential nutrients that would Washes out potential nutrients that would be availablebe available

Lost nutrients will negatively impact Lost nutrients will negatively impact plant diversityplant diversity

Why Soil Loss?

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

Soil types

Soils are weathered rocks that create Soils are weathered rocks that create smaller particles smaller particles

Classified as Sand, Silt or ClayClassified as Sand, Silt or Clay Depending on the location, there are greater Depending on the location, there are greater

compositions of soil types (i.e. New Jersey compositions of soil types (i.e. New Jersey coastal area has mostly sand, there clay coastal area has mostly sand, there clay soils in N. New Jerseysoils in N. New Jersey

Soil Contamination

Since soils are in the LITHOSPHERE Since soils are in the LITHOSPHERE (Crust), they will be exposed to more (Crust), they will be exposed to more environmental stresses.environmental stresses.

Acid rain is a problem in that it displaces Acid rain is a problem in that it displaces cations in the soil and causes changes in cations in the soil and causes changes in soil chemical compositions and pH soil chemical compositions and pH

Soil Texture = %Sand, Silt & Clay in a soil.

Soil texture is the single most important Soil texture is the single most important

physical property of the soil. Knowing physical property of the soil. Knowing

the soil texture alone will provide the soil texture alone will provide

information about: information about:

1) Infiltration of water1) Infiltration of water

2) Porosity2) Porosity

3) Nutrient holding ability3) Nutrient holding ability

Textural Triangle

Particle Diameter Size

Soil particle diameters Soil particle diameters range over 6 orders of range over 6 orders of magnitudemagnitude 2 m boulders 2 m boulders Coarse fragments > 2 mmCoarse fragments > 2 mm Sand < 2 mm to 0.05 mmSand < 2 mm to 0.05 mm Silt < 0.05 mm to 0.002 Silt < 0.05 mm to 0.002

mmmm Clay < 0.002 mClay < 0.002 m

Coarse Fragment > 2 mm> 2 mm

Gravels, cobbles, Gravels, cobbles, bouldersboulders

Not considered Not considered part of fine earth part of fine earth fraction fraction

Boulders left in Boulders left in valley of Big Horn valley of Big Horn Mts.(Wy) by a Mts.(Wy) by a glacier.glacier.

Sand < 2 mm to > 0.05 mm< 2 mm to > 0.05 mm

Visible without Visible without microscopemicroscope

Rounded or angular in Rounded or angular in shapeshape

Can contain quartz or Can contain quartz or calcium carbonate & calcium carbonate & sometimes mineralssometimes minerals

Feels GrittyFeels Gritty

Sand

Low specific surface areaLow specific surface area Sand has less nutrients Sand has less nutrients

for plants than smaller for plants than smaller particlesparticles

Voids between sand Voids between sand particles promote free particles promote free drainage and entry of airdrainage and entry of air

Holds little water and Holds little water and prone to droughtprone to drought

Silt

< 0.05 mm to > 0.002 < 0.05 mm to > 0.002 mmmm

Not visible without Not visible without microscopemicroscope

Quartz often dominant Quartz often dominant mineral in silt since mineral in silt since other minerals have other minerals have weathered away.weathered away.

Silt

Does not feel grittyDoes not feel gritty Floury feel –smooth Floury feel –smooth

like silly puttylike silly putty Wet silt does not Wet silt does not

exhibit stickiness / exhibit stickiness / plasticity / malleabilityplasticity / malleability

Silt Smaller particles – Smaller particles –

retains more water for retains more water for plants and have slower plants and have slower drainage than sand.drainage than sand.

Easily washed away by Easily washed away by flowing water – highly flowing water – highly erosive.erosive.

Holds more plant Holds more plant nutrients than sand.nutrients than sand.

Source of Silt

Clay Wet clay is very sticky Wet clay is very sticky

and is plastic or it can and is plastic or it can be molded readily.be molded readily.

Easily formed into long Easily formed into long ribbons. ribbons.

Shrink swell – none to Shrink swell – none to considerable depending considerable depending on the kind of clay.on the kind of clay.

Clay

Pores spaces are very Pores spaces are very small and convoluted small and convoluted Movement of water and air Movement of water and air

very slowvery slow Water holding capacity Water holding capacity

Tremendous capacity to Tremendous capacity to adsorb water- not all adsorb water- not all available for plants.available for plants.

Soil strength- shrink/swell Soil strength- shrink/swell affects buildings, roads affects buildings, roads and walls.and walls.

Chemical adsorption is Chemical adsorption is largelarge

Determining Soil Texture - Feel Method

Wet soil in handWet soil in hand Make ribbonMake ribbon Length of ribbon Length of ribbon

indicates clay contentindicates clay content Grit or lack of grit Grit or lack of grit

indicates sand or siltindicates sand or silt Smoothness indicates Smoothness indicates

siltsilt

USDA Textural Classes

Sandy soils (coarse)Sandy soils (coarse) Fine sandFine sand Very fine sandVery fine sand

Loamy soils (medium)Loamy soils (medium)

Clayey soils (fineClayey soils (fine))

Sandy Soils

Coarse Coarse texturetexture SandsSands Loamy Loamy

sandssands

Changes in soil texture

Over long periods Over long periods (1000s yrs) (1000s yrs) pedologic processes pedologic processes alter soil horizon alter soil horizon textures.textures.

As soils get older As soils get older sand weathers to sand weathers to silt and silt silt and silt weathers to weathers to clay….therefore old clay….therefore old soils have more soils have more clay.clay.

Naming Soil Horizons

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

Naming soil Naming soil horizons takes horizons takes practicepractice

Organic Horizons

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

A horizon - surface A horizon - surface horizons that accumulate horizons that accumulate

B horizon – usually iron and B horizon – usually iron and leached minerals locallyleached minerals locally

C horizon – more rock and C horizon – more rock and “parent material” “parent material”

A B

B (t)

B (C)

C