SOIL SURVEY TECHNOLOGY OVERVIEW

Michael A. WilsonResearch Soil Scientist

USDA-NRCS National Soil Survey CenterLincoln, NE

OBJECTIVESUseful tools for answering questions

about soil properties

• Soil Survey Office Labs• Active C• VNIR• Portable X-ray Fluorescence• Climate stations• Isotic/Spodic • Geophysical tools

SSO Laboratories—Your lab

• Field kits provide opportunity to collect limited data to answer specific questions

• Not a replacement for NSSC KSSL– Lower accuracy/higher detection limits– Less efficient

• Why use field kits?– Check of certain properties as part of map unit

evaluation or mapping– Rapid turn around of data – Prescreening pedons for SSL analysis

Types of Analyses

• Particle size distribution - hydrometer

• Chemical properties– pH– EC– Hach kit

• Base saturation• Extractable cations• Salts

• CaCO3 equivalent

• Gypsum content• Active C• Isotic / Spodic properties

http://soils.usda.gov/technical/index.html#lab_ref

Field methods available to use are documented in this 2009 Manual

Laboratory Safety

• Not a trivial matter• Protect yourself and others• Use common sense• OSHA citation

ftp://ftp-fc.sc.egov.usda.gov/NSSC/Lab_References/safety_guide.pdf

Soil Survey Office Laboratory Safety

Manual is available on-line

MSDSMaterial Safety Data Sheet

• Information regarding the proper procedures for handling, storing, and disposing of chemical substances

• Required to be read, kept, and stored in lab in organized manner

ftp://ftp-fc.sc.egov.usda.gov/NSSC/Lab_References/chem_disposal.pdf

Chemical Hygiene Plan

• Document you write for your lab

• Policies, procedures, and responsibilities to protect employees from the health hazards of chemicals used

• OSHA’s Occupational Exposure to Hazardous Chemicals in Laboratories Standard details requirements of a CHP to protect persons from hazardous chemicals

• CHP has required elementshttp://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=10106

Soil Survey Technologiesto Discuss

• Active C• VNIR• Portable X-ray Fluorescence• Spodic Field Kit• Climate Stations • Geophysical tools

Active Carbon Kit

C. Stiles, et al., 2011. Validation Testing of a Portable Kit forMeasuring an Active Soil Carbon Fraction. Soil Sci. Soc. Am. J. 75:2330–2340

Active Carbon Analysis

• Potassium Permanganate -- weak oxidant of organic C

• Active (labile) C is the biologically active fraction

• Soil Health/Soil Quality Indicator of active food web, microbial biomass, and nutrient cycling

• Has been shown to be related to tillage systems– Early indicator of C degradation

Active C:Total C Ratio

AL CA ID IA MO OR VA0

200

400

600

800

1000

1200

1400

1600

1800A

C:T

C

Acitive C related to total C but not consistently

Visible Near IfraRed Diffuse Reflectance Spectroscopy

• Chemical bonds interact with Visible and IR energy – Different bonds – different wavelengths

Atomic Bond EnergyVibrationBendingRotation

Visible Near IfraRed Spectroscopy

• Amount of interaction proportional to quantity

– Measurement is spectrum– Statistical prediction based

on spectral library

• Soil minerals– Si-O bonds– Al-O bonds– Bond energy varies with

mineralogy

• Organic matter– C-O bonds– C-H bonds

VNIR –Measures spectral signatures of materials defined by their reflectance as a function of wavelength. Signatures are due to electronic transitions of atoms and vibrational stretching and bending of structural groups of atoms that form molecules and crystals.

Visible to Near Infrared Diffuse Reflectance Spectroscopy

• VNIR-DRS– Measures reflectance

at a wide range of wavelengths

– 350-2500 nm– Rapid: 100 readings

per second– Interaction with

sample composition and matrix produces diffuse reflectance Soil

Diffuse Reflectance

Fiber Optic Light Source

Spectral Radiometer

Data Collection

• Portable VNIR spectrometers

– 1 per MO

• Spectra measurements– ~1 min/depth

• Predictive models developed at SSL

– Organic and inorganic C– Other properties as

appropriate

Benefits of VNIR

• Little or no sample prep– Field analysis of moist soils may be

possible• Possible to collect spectra in the field• Spectra can be used to predict multiple

properties• Useful for rapid collection of data on many

samples– Traditional lab methods more accurate

for a limited number of samples

Clay Content

Estimated Clay (%)

Mea

sure

d Cl

ay (%

)

Estimated Clay (%)

Mea

sure

d Cl

ay (%

)Calibration Test Data

Cation Exchange (NH4OAc)

Estimated CEC (meq 100g-1)

Mea

sure

d CE

C (m

eq 1

00g-1

)

Estimated CEC (meq 100g-1)

Mea

sure

d CE

C (m

eq 1

00g-1

)

Calibration Test Data

Soil Organic Carbon (Leco)

R2 = 0.9PLSR R2 = 0.82RMSE = 0.15RPD = 2.4

Portable X-ray Fluorescence Spectroscopy

Different Manufacturers

Bruker Tracer IV-SD

Oxford X-MET 5000

Olympus Innov-X Delta RXF

Thermo Scientific Niton XL2 GOLDD

QSX Quickshot

VNIRXRF

X-ray fluorescence (XRF) is used to detect and measure the concentration of elements in substances.

Fluorescence - phenomena of absorbing incoming radiation and re-radiating it as lower-energy radiation.

When exposed to x-rays, electrons are ejected from inner orbitals

Subsequently, electrons of higher energy orbitals fall into the lower orbitals. A fluorescent photon with a characteristic energy is released.

Key Point: Atoms fluoresce at specific energies when excited by X-rays.

Energy source: X-ray tube or radioisotope

X-ray fluorescence (XRF)

•Excitation source is either: X-ray tube with target of Ag (silver), Ta (tantalum), Au (gold), Rh (rhodium), W (Tungston)

Radioisotope (e.g., Fe-55, Co-57, Cd-109)

•Analysis covers area of 1 cm2 to a depth of approximately 2mm

•Minimum set up and calibration required (Factory Calibrated with alloy chip)

•Proper training is essential--User must understand the dangers of x-rays and fundamentals of radiation protection

Facts of Portable XRF

Advantages of Portable XRF

•Rapid field analysis and ease of use.

•Portable and easily transported to job sites; can check on an airplane as baggage or carry-on •Delivers qualitative and/or quantitative multi-element analysis; simultaneous determination

•Can be used on many different samples - solids, powders, liquids, etc.

•Little or no sample preparation required

Elements quantified by XRF

•Very difficult to detect or quantify lighter elements e.g., Si, Al, Li, Be, P, B, C

Comparison of Detection Limits for ICP and PXRD

SSL InnovXAnalyte Acid Digestion; ICP 3-beam; Ta/Au tube

------------------------ mg kg-1 -----------------------

Al 31 5000Ca 9 25Fe 3 5K 34 40

Mg 5 10000Mn 1 4Na 28 No detectionP 29 600

As 0.0001 2Cd 0.0001 7Cr 0.0062 8Cu 0.0002 6Hg 0.0001 3Ni 0.0009 15Pb 0.0001 3Zn 0.0006 4     

PXRF is viewed by EPA as a screening method

Limitation of Portable XRF

Multiple applications in soils survey for element specific measurements

• Geographic profiling of elemental constituents in profiles

• Target elemental concentration in calcic, gypsic, spodic, placic horizons

• Mapping/spatial variability of contaminants across landscape

• Assist in selection of sites for sample collection

Spodic Field Kit

• Humic Fulvic Color—indicates translocation and accumulation of organic complexes in spodic horizons. (Holmgren and Holzhey, 1984).

• KOH extraction of Al – Comparable to acid oxalate

extractable Al

If KOH-Al >2%, P retention is generally 100% and likely andic soil properties.

In Spodosols, a level of 0.7% KOH-Al has been found to indicate the presence of a spodic horizon if the ratio of Al in the spodic material to that in the E horizon is >2.

Data loggers –

•Compact, battery-powered device to records measurements at set intervals over a period of time.•Record temperature, relative humidity, differential pressure, light intensity, water level, soil moisture, rainfall, wind speed and direction.

Climate Stations and Data Loggers•Deb Harms

Climate StationApplications to Soil Survey

• To define the line between soil climate regimes

• Supporting data to determine landscape and soil hydrology  

• Determine soil temperature vs air temperature off-sets for the region

•Measure soil temperature and soil moisture by volume   •Can include air temperature sensors and tipping-bucket rain gauge

•The stations are self contained and battery powered charged with a solar panel •Store the data up to one year and then need to be manually downloaded.    Possible to purchase cell phone system so the sites can be downloaded remotely.

Soil Climate Stations

Wells/Piezometers

Geophysical Methods

• Jim Doolittle (PA)• Wes Tuttle (NC)• Several states have equipment and operators

Electromagnetic Induction (EMI) Ground-Penetrating Radar (GPR)

Ground Penetrating RadarPrincipal Soil Survey Uses

Determine the presence, depth, and lateral extent of subsurface horizons, stratigraphic and lithologic layers.

Improve interpretations by providing estimates of soil map unit composition.

Characterize spatial and temporal variations in soil

properties.

In the conterminous USA, only 22 % of the soils are considered well suited to GPR.

Use of GPR for soil survey investigations is limited by the

medium.

About 36 % of the soils are considered poorly suited to GPR,

GPR ApplicationCharacterization of Peatlands

GPR Application-- Soil Depth Determinations

Rock fragments limit the effectiveness of conventional soil survey tools.

One of the most effective uses of GPR has been to chart bedrock depths and determine the taxonomic composition of soil map units based on soil-depth criteria.

GPR Application Characterizing Subaqueous Soils

Subaqueous SoilsGPR can provide data on fresh water depths,

subbottom topographies, and sediment types.

GPR Application Preferential Flow Paths

The movement of water through soil is not uniform and is strongly influenced by soil layering.

Discontinuities provide narrow flow paths that account for a significant proportion of the water and contaminants moved thru the soil.

GPR Application Depth and Continuity of Water Restricting Layers

Cisne - Fine, smectitic, mesic Mollic Albaqualfs

Darley - Fine, kaolinitic, thermic Typic Hapludults

Electromagnetic Induction (EMI)

THE ELECTRICAL CONDUCTIVITY OF SOILS IS INFLUENCED BY:

1) THE TYPE AND CONCENTRATION OF IONS IN SOLUTION.2) THE AMOUNT AND TYPE OF CLAYS IN THE SOIL MATRIX.3) THE VOLUMETRIC WATER CONTENT. 4) THE TEMPERATURE AND PHASE OF THE SOIL WATER.

THE APPARENT CONDUCTIVITY OF SOILS

WILL INCREASE WITH INCREASING:

Water

Clay

Soluble salt

EMI Application High-Intensity Soil Surveys

Identification and delineation of small inclusions of dissimilar soils within generalized soil polygons.

EMI Application Characterization of spatial soil variability

666600 666610 666620 666630 666640 666650 666660 666670 666680 666690

Easting

3039120

3039130

3039140

3039150

3039160

3039170

3039180

Nor

thin

g

05010015020025030035040045050055060065070075080085090095010001050

m S/m

EMI can provide a level of resolution not practical with traditional soil survey tools and methods

Menfro – Fine-silty, mixed,

superactive, mesic Typic Hapludalfs

EMI Application Identifying soil-hydrologic-landscape units

EMI Application Spatiotemporal variations in ECa

associated with changes in soil moisture.

EMI Application Characterizing and mapping anthropogenic soils

EMI Application Identifying the presence and extent of soil contaminants

EMI Application Management of saline soils

CONCLUSIONS

• Methods and equipment are available to assist in understanding properties of soils and landscapes

• Document your plan: why needed, type of data to be measured, your plans to use

• If you have a question, ask