USDA-NRCS PROTOCOLS: Soil Mapping/Sample Collection

M.A. Wilson and S.J. Indorante

OBJECTIVES

• Geographic partitioning of soils

• Scales of data compilation / availability

• Sample collection protocols

To discuss:

NATIONAL COOPERATIVE SOIL

SURVEYDetermines geographic

distribution of soils:•landscape models•maps•map unit/series descriptions•point analytical data•taxonomic classifications•interpretations/predictions

SOIL• A natural body composed of solids,

liquids, and gases that occur on the land surface, occupying space, with one or more of the following:

• Horizons or layers distinguishable from parent material by pedogenic processes

• Ability to support rooted plants in a natural environment

Soil Genesis ModelS = f (CL, O, R, P, T)

•Climate•Organisms•Relief•Parent Material•Time

Factors interactto create naturalbodies on the landscape in a predictable manner

Soil-Landscape Paradigm

• In a geographic area, only a small number of repeating soil-landscape units occur

• Observable discontinuities exist between conterminous areas of different soil-landscape units

Minimum Order of Delineation

Soil Survey Map Scale Sizeacres/ ha

Order 1 1:5,000 0.25/ 0.10

Order 2 1:12,000 1.43/ 0.61:24,000 5.7/ 2.3

Order 3 1:31,680 10.0/ 4.1

Order 4 1:62,500 39/ 15.8

Order 5 1:250,000 623/ 252

Common Mapping ScalesUsed in Soil Survey

Mapping Soil GeographyLandscape (1:100,000)

Soil-Landscape Units(Landscape Scale)

General ParentLandform Material

Upland Loess

Valley side Loess/colluvium

Flood plain Alluvium

Mapping Soil GeographyLandform and Components

(1:25,000)

Soil-Landscape Units(Landform Component Scale)

General Geomorphic (Landform)Landform Component Hillside Profile Elements

Upland Interfluve, Side & Nose Slope Summit, Shoulder, Backslope, Footslope

Head Slope Footslope, Toeslope

Valley side Interfluve, Side & Nose Slope Summit, Shoulder, Backslope, Footslope

Flood plain ------------------- Footslope, Toeslope

Map Unit Label

The Mapped Soils

General Slope Erosion Map UnitLandform Soil Series Range % Class Label

Upland Menfro 2 to 5 79B5 to 10 Severe 79C310 to 18 Severe 79D318 to 25 Severe 79E3

Winfield 5 to 10 Severe 477C3

Valley side Drury 2 to 5 75B

Flood plain Haymond 2 to 5 8331BWakeland 0 to 2 3333A

Dupo 0 to 2 3180A

Mapping Unitsare the basic units for identifyingsoil geographic orderin a soil survey

Soil Correlation

“Natural families of soil delineations that can be interpreted similarly are the ultimate and elusive goal of soil mapping and classification.”

(Hudson, 1992)

The natural families created are mapping units.

Systematic Variability of Soil Properties

• Attributable to a known cause• Gradual or marked change in

properties related to landform, geomorphic elements, and soil forming factors.

• Distribution patterns must be related to landscapes and geomorphic surfaces for effective soil survey operations.

(Wilding and Drees, 1983)

Problems of Scale

• Variations in soil properties range from megascopic (physiographic region and landforms) to microscopic in scale.

• Relationship between systematic and random variability is likely to be scale dependent.

(Upchurch and Edmonds, 1991)

Sample CollectionProtocols

PEDON

Smallest volume of soil that can be used to describe and sample the soil to represent the landscape unit

Minimal horizontal area is 1m2, but can range to 10m2 depending on variability

PEDON

•Sampled by NRCS scientists and National Cooperative Soil Survey (NCSS) partners at universities, state, and other federal agencies.

•Sites are usually selected to represent a central concept of a soil series.

TYPICAL PEDON:Sharkey clay--planed and smoothed, cultivated field. (Colors arefor moist soil unless otherwise stated.)

Ap1--0 to 6 inches; very dark grayish brown (10YR 3/ 2) clay;structureless, massive; firm; very sticky; very plastic; few fineroots; few fine pores; few stresscracks; common fine distinct darkyellowish brown (10YR 4/ 4) masses of iron accumulation arounddead roots; few fine faint dark gray (10YR 4/ 1) iron depletionsaround some root channels and pores; slightly acid; clear smoothboundary.

Bssg1--10 to 24 inches; dark gray (10YR 4/ 1) clay (color for pedinteriors and faces); weak medium subangular blocky structureparting to moderate fineangular blocky; very firm; very sticky; veryplastic; few fine roots; few fine grooved intersecting slickensidesthat form coarse wedge-shaped aggregates; shinypressure faceson some peds; common medium distinct dark yellowish brown(10YR 4/ 4) masses of iron accumulation in matrix and on faces ofpeds; few fineprominent strong brown (7.5YR 5/ 6) masses of ironaccumulation on faces of some peds; neutral; gradual wavyboundary.

.

DETAILED MORPHOLOGY

Soil Taxonomy

•Classification system used by the NCSS for identifying and labeling soils in mapping units.

•Nomenclature identifies soil properties

Order: Vertisols

Suborder: Aquerts

Great Group: Epiaquerts

Subgroup: Chromic Epiaquerts

Family: Very-fine, smectitic, thermicSeries: Sharkey

SOIL SERIES• Lowest category in the U.S. System of

Soil Taxonomy

• Conceptualized class of soil bodies on the earth’s surface

• More restrictive limits than higher taxa.

• Soil series serve as the means to transfer soil information and research knowledge from one soil area to another.

SHARKEY SERIESLOCATION:LA+AR KY MO MS TN

The Sharkey series consists of very deep, poorly andvery poorly drained, very slowly permeable soils thatformed in clayey alluvium.These soils are on floodplains and low terraces of theMississippi River; MLRA 131. Slope is dominantly lessthan 1 percent, but ranges to 5 percent.

TAXONOMIC CLASS: Very-fine, smectitic, thermicChromic Epiaquerts

TYPE LOCATION: Madison Parish, Louisiana; NE 1/ 4, SE 1/ 4, SE 1/ 4,Sec.33, T.17 N., R.13 E.; 32 degrees, 26minutes,19.51 seconds N. Latitude; 91 degrees, 9 minutes,55.64 seconds W. Longitude; Tallulah Quadrangle,Louisiana

OFFICIAL SERIES DESCRIPTION

RANGE IN CHARACTERISTICS:

Solum thickness ranges from 36 to more than 80 inches.

In most years, cracks 1 to 3 cm wide develop to a depth of 20 to 24inches or more. COLE ranges from about 0.10 to 0.17 throughout the Bg,Bssg and Bssyg horizons.

Clay content in the 10-40 inch control section ranges from 60 to 90percent.

Some pedons are calcareous below 20 inches.

Clayey buried A horizons are present in some pedons below a depth of 20inches.

A horizon has hue of 10YR, value of 2 to 4, and chroma of 1 or 2. Textureis clay, silty clay, or silty clay loam with more than 30 percent clay.

SERIES RANGE IN PROPERTIES

GEOGRAPHICALLY ASSOCIATED SOILS: These arethe Alligator, Bowdre, Commerce, Dundee, Earle,Mhoon, Newellton and Tunica series. Alligator soilsoccur on similar landscapes, but are more acid in theupper part of the subsoil.

DRAINAGE AND PERMEABILITY: Most pedons ofSharkey are considered artificially drained and nolonger develop aquic conditions.

USE AND VEGETATION: Used mostly for cropland;soybeans and rice are the principal crops.

DISTRIBUTION AND EXTENT: Mississippi River floodplain and low terraces in Arkansas, Louisiana,Kentucky, Mississippi, Missouri, and Tennessee.The series is of large extent.

MLRA OFFICE RESPONSIBLE: Little Rock, Arkansas

SERIES ESTABLISHED: Yazoo area, Yazoo County,Mississippi; 1901.

The Pedon Concept--

Extending limited point data to geographic coverage

Measurement Observation

Soil Observationand Measurement -Pedon Data

Soil Observationand Measurement -Pedon Data

AA

BB

CC

RR

Land resource Regions

Map based on STATSGO data

MapBased on SSURGOData

CONCLUSIONS

• The National Cooperative Soil Survey uses the model of soil genesis and the soil landscape paradigm to define landform components and soils.

• Products include point morphological/analytical data with maps at various scales designed for land-use planning and interpretations.