Welcome to the 2004 Massachusetts Envirothon Workshop

Soils Overview Workshop

Part IIITom Cochran

USDA-NRCS Franklin Co., MASome material courtesy of Jim Turenne

USDA-NRCS, Rhode Island

So what?Physical differencesThe size of sand and clay give a horizon different physical & chemical properties.Sand particles are much larger than clay particles and, sand is blocky shaped while clay is platy.A collection of sand particles create air spaces that are larger and more connected than those created by a collection of clay particles.

Chemical differencesSand particles have no charge on their surface.

Clay particles have negative charge on their surface and adsorb elemental nutrients such as Ca, Mg, Fe, NO3, PO4.

Particle surface areaA sand particle that is 1 mm in diameter has a volume of approximately 0.5 mm3 and a surface area of 6mm2 with no electrical charge.

A clay particle (0.002mm dia.) has a volume of approximately 4 x 10-9 mm3, so 12.5 million clay particles will fit inside the 1-mm sand particle.

Each clay particle has a surface area of about 0.012 mm2. Therefore, 12.5 million clay particles will provide 150,000 mm2 of surface area with negative charge sites.

The colloidal surface area of a 15-cm thick slice of a hectare of clay soil could be 700,000 km2 (270,000 mi2), which is greater than the area of France (Brady & Weil, 1996).

Soil StructureDefinition: Soil structure is the natural organization of soil particles into units called peds.

When structure is examined, its type, grade, & size is determined, and recorded in that order.

Most structure types in New England are granular, subangular blocky, massive, or single grain because clay contents are usually less than 40%.

Grades:Structureless – no discrete unit observableWeak – units are barely observableModerate – unit well-formed & evidentStrong – units are distinct and separate cleanly when disturbed

Granular crumb size units; often associated with A horizons that contain organic material

Sub-angular blocky rounded edges and faces; often associated with B horizons

MassiveNo structural units; material is a coherent mass

Single grainNo structural units; loose sand

Names for structure size are as follows, and size values vary by the structural type.

For all structure except platy,Very fineFine MediumCoarseVery coarseExtremely coarse

For platy structure,Very thinThinMediumThickVery thickExtremely coarse

Soil structural size

Soil ColorThe end product of organic matter decomposition is humus, which is a black color that stains surfaces. The humus is responsible for most of the black colors of an A horizon.

Iron oxide coats soil particles and gives them the reddish-brown color of rust. Sand grains are mostly quartz material, which is naturally a gray color. Red sand is just quartz coated with iron rust.

Mottling in a well-drained soil is usually due to the mineral coatings on the particles.Mottling in wetter soils can be caused by the reduction of the iron in the coatings.

Major Forms of Iron and Effect on Soil Color

Form Chemical Formula ColorFerrous oxide FeO Gray

Ferric oxide (Hematite) Fe2O3 Red

Hydrated ferric oxide (Limonite) 2Fe2O3 3H2O Yellow

Soil Color Book

The Munsell color book is used to document color in a standard notation.

Hue: Dominant spectral color. Value found in th top right-hand corner of each page.

Value: The degree of light/dark of a color in relation to a neutral gray scale. Values along the left-hand side of each page.

Chroma: Strength of hue. Values along the bottom of each page.

The 10YR page of the Munsell color book.

Reading Soil ColorsReading Soil Colors

Optimum conditionsNatural lightNatural lightClear, sunny dayClear, sunny dayMiddayMiddayLight at right anglesLight at right anglesSoil moistSoil moistNO sunglasses!NO sunglasses!

Redoximorphic features

microbes

Eating OM = e-Free electrons

In the presence of air, free oxygen molecules (O2) take the electrons (reduction), but when the soil is saturated there is no free O2.

Under saturated conditions other oxidized molecules take the electrons in this order.NO3 Fe2O3 SO4 CO2

Nitrate rust sulfate carbon dioxideScientists use the reduction of rust as an indicator of frequent saturated conditions because it is the first reduction reaction that can be seen by the naked eye.

Redoximorphic features continued

Rust is the oxidated state of iron (Fe2O3). Under saturated conditions, the free electrons produced by microbial respiration remove the O3 from the iron. The O3 then forms water with the hydrogen ions that are plentiful in soil solution.

6e- + 6H+ + Fe2O3 ------ 2Fe2+ + 3H2O

The iron ion (Fe2+) is soluble in the soil solution, and as the water drains from the soil the iron moves with it.

This causes the iron to be removed from the particle coatings and be either completely removed from the soil profile or deposited in another place in the profile.

Scientists interpret the absence of iron and the patterns of iron concentrations when evaluating the drainage class of a soil.

Redoximorphic FeaturesRedoximorphic Features

After the matrix color is After the matrix color is determined, record the determined, record the color patterns of the color patterns of the redox features if present.redox features if present.

Can be very complex.Can be very complex.

Describe color, abundance, Describe color, abundance, size, contrast, shape, and size, contrast, shape, and location.location.

Contrast of RedoxContrast of RedoxContrast refers to the degree of Contrast refers to the degree of

visual distinction between visual distinction between associated colorsassociated colors

Faint -- evident only on -- evident only on close examination.close examination.

Distinct -- readily seen.-- readily seen.

Prominent -- contrasts -- contrasts strongly. strongly.

Abundance and Size of RedoxAbundance and Size of Redox

AbundanceFew -- less than 2% -- less than 2%

Common -- 2 to 20% -- 2 to 20%

Many -- more than 20% -- more than 20%

SizeSizeFine -- < 5 mm -- < 5 mm

Medium -- 5 to 15 mm-- 5 to 15 mm

Coarse -- > 15 mm -- > 15 mm

Soil Drainage ClassesDrainage class is determined in the field by observing landscape position and interpreting redoximorphic features.The table below is used to interpret the redoximorphic features.Drainage classDrainage class 2 Chroma 2 Chroma

depletionsdepletionsWater Table Water Table DepthDepth

Gray Gray matrixmatrix

Water Table Water Table DepthDepth

Very poorly 0-12” w/umbric 0-1 ft. 0-12” 0-12”

Poorly 0-12” w/ochric 0-1 ft. 6-12” 0-12”

Somewhat poorly 12-18” 1-2 ft. 12-24” 12-24”

Moderately well 18-36” 2-4 ft. 24-48” 24-48”

Well >36” >4 ft. >48” >48”

Somewhat excessive >36” >5 ft. >48” >48”

Excessively >36” >5 ft. >48” >48”

Using a Soil surveyOrganization:Begins with general descriptions of survey area. Information about the soil forming factors is found here.

Next, are detailed descriptions of each soil map unit.

Typically, information includes profile depth drainage class topographic position HorizonationPermeability Available water capacitypH range agricultural suitabilityWoodland suitability urban development suitabilityCapability subclass suitability

Organization (continued)

The Use and Management of the Soils section follows the detailed descriptions. This section explains the interpretations presented in the tables that follow, which includeYields per AcreLand capability classificationWoodland Management & productivityRecreational usesWildlife habitatEngineering usesBuilding site developmentWaste applicationsConstruction material suitabilityWater management

Using the interpretation tablesLet’s practice by using a few of the Tables.

We will use Table 11 (Building Site Development) from the Worcester Co. South survey to determine the suitability of a Paxton soil for a dwelling with a basement.

We find the map unit of interest in the left-hand column of Table 11 and the use of interest in the top row. At the intersection of this column and row is the interpretation.

Page 61 of the Use and Management of Soils section explains the meaning of the interpretation listed in the table.

Next, let’s see if we can economically install an on-site sewage treatment system with our dwelling.

We will need to use Table 12 (Sanitary Facilities) to see if there are any limitations to the operation of a septic absorption field.

Again, page 61 of the Use and Management of Soils section explains the meaning of the interpretation listed in the table.

Septic tank absorption field ponding on surface.

Farmland InterpretationsFarmland Interpretations

Look for thick dark topsoil Look for thick dark topsoil layer.layer.

Textures of upper 20 inches Textures of upper 20 inches should not be too sandy.should not be too sandy.

No large stones or boulders.No large stones or boulders.

Not too steep, slope < 8%.Not too steep, slope < 8%.

Site may be wooded.Site may be wooded.