Interpreting Soils DataMaggie Payne

Resource Soil ScientistUSDA NRCS

maggie.payne@ma.usda.gov

Massachusetts Soil ConferenceHeifer Farm, Rutland, MA

September 17, 2015

Core Mission of the Soil Survey Program

1. Make an inventory of the soil resources of the U.S.2. Keep the soil survey relevant to ever-changing needs3. Interpret the information and make it available in a useful form4. Promote the soil survey and provide technical assistance in its use

for a wide range of community planning an resource development issues related to non-farm and farm uses

Soil Data Organization

Soil Survey Legend Consists of:• Soil Map Unit (with a minimum map unit size)

• Soil Component/Soil Series (estimate purity of map unit)• Soil Horizons (typical pedon for soil survey area)

• A• Depth, texture, color, pH, bulk density, Ksat…..

• B• Multiple data elements for each horizon

• C

Housed in NASIS – National Soil Information System

Soil Map Unit

Minor Components

Named Component

National Soil Information System

Pedon

Lab

Range

Forest

SoilMap

Manuscripttext

NASISdatabase

PlantData

SoilData

ClimateData

DOQs

Soil SurveyReport

CST

FOTG

CustomReports

SSURGO

Field Data CollectionPublic Data Customer

Products

Manage Soil Data

Analyze/Summarize

Crops

NASIS the “Data Management System”

Making this:

Into this:

Soils Reports and Interpretations:

• Soil Properties• Observed in the field or measured in the lab

• Sand, silt, clay fractions, organic matter, bulk density, flooding, water table

• Calculated Soil Qualities• Calculated based on soil properties

• Texture, Hydrologic soil group, T factor, Available water capacity

• Interpretations• Suitabilities and Limitations• Using observed or calculated data to predict soil behavior under defined conditions

• Uses outside research to determine which soil characteristics to use• Septic tank absorption fields• Vegetation suitability index• Suitability for excavated ponds

Soil Properties and Interpretations:

Calculated Soil QualitiesHydrologic Soil Groups (HSG)

4 groups according to the rate of water infiltration (A, B, C, and D):• Group A: high infiltration rate

• deep, well drained to excessively drained sands or gravelly sands

• Group B: moderate infiltration rate• moderately deep or deep, moderately well drained or well drained soils that have moderately fine

texture to moderately coarse texture

• Group C: slow infiltration rate• Usually have a layer that impedes the downward movement of water or a moderately fine or fine

texture

• Group D: very slow infiltration rate (high runoff potential)• clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan

or clay layer at or near the surface, and soils that are shallow over nearly impervious material

• A dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes.

Data elements used in the HSG calculation

• horizon depth• Ksat

• restriction depth• restriction kind

Data elements used• Flooding and Ponding frequency

and duration

HSG CalculationResults:

Interpretations

• Soil survey interpretations predict soil behavior for specified soil uses and under specified soil management practices.

• Laws, programs, and regulations • Broad land use planning

• The accuracy of the prediction depends on the how well the data is populated and the completeness of the criteria.

• Need to be written with the participant who works with the intended use

Soil Interpretation CriteriaStep 1. Define the Activity Step 2. Separate Aspects Step 3. Identify Site Features Step 4. List Soil Properties Step 5. Select the Number of Separations Step 6. Document AssumptionsStep 7. Develop the Criteria Table Step 8. Application, Presentation, and Testing

Creating Soil Interpretations

Define the Activity

• Sites should be dry and level to assure walking comfort and suitable sites for tables and benches.

• Deep soils are preferred to maintain suitable grass cover to overcome excessive compaction due to traffic.

• Picnic areas will use concrete tables and benches and small loaders will be used during placement.

• These sites may also be suitable for hiking areas and playgrounds. • The areas will encompass a minimum of 5 acres, however some may be as small as

1 acre. The interpretation will be used by the county for broad land use identification of areas suitable for picnic areas.

Creating Soil Interpretations

A town is looking to purchase land to create new park and recreational areas. They wish to design criteria that will identify sites suitable for picnic areas.

Separate Aspects

• What is considered?Is this an interpretation for installation ease, longevity, etc

• Do we need multiple interpretations?

Creating Soil Interpretations

Identify Site Features

There are factors that are not soil properties that will need to be considered – these are not written into a soil interpretation, but considered at a later time.• geographical location• rainfall totals• amount of surface stones

Creating Soil Interpretations

List Soil Properties• The soil properties impacting the site selection for picnic areas will

include those influencing water infiltration, soil water movement, properties that affect trafficability and vegetation growth.

Creating Soil Interpretations

• Organic matter• Flooding

• Stones• Permeability• Ponding

• Sand• Bedrock

• Depth to impermeable layer• Slope

• Gravel content• Acidity• Clay content

• Water Table

Evaluating Soil Properties• Soils with a water table from the surface to 50 cm are too wet• Soils with a water table greater than 200 cm from the surface are not too wet• Soils with a water table between the ranges will be evaluated using a sigmoid

curve

Creating Soil Interpretations

Select the Number of Separations• As a picnic area interpretation designed for broad land use planning, it is decided to create three

separations to be named “Not Limited”, “Somewhat Limited”, and “Very Limited”.

Creating Soil Interpretations

Document Assumptions• Document assumptions about the significance of the property and established values for

separating criteria. (a) A record of the significance of the water table and the slope properties(b) Indicate why the feature is important and why the specific break was chosen –

Why was 200 cm chosen? Why was 15 percent chosen?

(c) Establish values that are significant to the interpretation – based on research

Develop the Criteria Table• Assign feature and impact terms, and develop the criteria table

Creating Soil Interpretations

Property Limits Restriction

Not Limited Somewhat Limited Very Limited

Flooding None Others Freq, V. Freq Flooding

Water Table >200 50-200 <50 Too Wet

Texture S, LS, C, SiCL

Ksat

Slope <8 8-15 >15 Too Steep

• A landowner wants assistance in building a pond.

• Define the Activity:

Using Soil Interpretations – Example 2

• describe the activity or use; • identify the function(s) of the

activity or use; • define the desired performance

of the activity or use; • specify the soil depths that are

affected; • identify the type of equipment

for installation;

• Pond Reservoir Area• Livestock Water

• Hold water most of the year

• 3 meters (10 feet deep)

• D8 dozer

We have an interpretation for that: Pond Reservoir Rating Map

Using Soil Interpretations

Disclaimer:

Sometimes you’ve got to dig a hole

Using Soil Interpretations

Evaluating Soil PropertiesProperty Limits Restriction

Not Limited

Somewhat Limited

Very Limited

Perm 50-180cm

<1um/s 1-14 >14 Seepage

Bedrock >150 50-150 <50 BedrockTexture Marl Excess lime

Texture Gyp Excess gyp

Slope <3 3-8 >8 Too Steep

Using Soil Interpretations

Getting interpretive maps and reports

• Web Soil Survey

• Access Database from Geospatial Data Gateway

• Soil Data Viewer

Web Soil Survey

Web Soil Survey

Soil Access Database

Soil Data Viewer

Soil Data Viewer

Statewide maps – Website content

Developing new interpretations and reports

Are there certain soil properties that you need for a particular use?

We can make a report or interpretation for that!