SOIL SURVEY TECHNOLOGY OVERVIEW Michael A. Wilson Research Soil Scientist USDA-NRCS National Soil Survey Center Lincoln, 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
Soil Survey Office Laboratory Safety Manual is available on-line ftp://ftp-fc.sc.egov.usda.gov/NSSC/Lab_References/safety_guide.pdf
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 elements http://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 for Measuring 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 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 Energy Vibration Bending Rotation
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 Spectral Radiometer Fiber Optic Light Source Diffuse Reflectance Soil
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 Measured Clay (%) Measured Clay (%) Calibration Test Data Estimated Clay (%) Estimated Clay (%)
Cation Exchange (NH4OAc) Measured CEC (meq 100g-1) Measured CEC (meq 100g-1) Calibration Test Data Estimated CEC (meq 100g-1) Estimated CEC (meq 100g-1)
Soil Organic Carbon (Leco) R2 = 0.9 PLSR R2 = 0.82 RMSE = 0.15 RPD = 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
XRF VNIR 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.
Key Point: Atoms fluoresce at specific energies when excited by X-rays. Energy source: X-ray tube or radioisotope X-ray fluorescence (XRF) Subsequently, electrons of higher energy orbitals fall into the lower orbitals. A fluorescent photon with a characteristic energy is released. When exposed to x-rays, electrons are ejected from inner orbitals
Facts of Portable 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
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
Very difficult to detect or quantify lighter elements e.g., Si, Al, Li, Be, P, B, C Elements quantified by XRF
Limitation of Portable XRF PXRF is viewed by EPA as a screening method
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 • HumicFulvic 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.
Climate Stations and Data Loggers • Deb Harms • 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 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
Soil Climate Stations • 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.
Geophysical Methods • Jim Doolittle (PA) • Wes Tuttle (NC) • Several states have equipment and operators Ground-Penetrating Radar (GPR) Electromagnetic Induction (EMI)
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.
Use of GPR for soil survey investigations is limited by the medium. • In the conterminous USA, only 22 % of the soils are considered well suited to GPR. About 36 % of the soils are considered poorly suited to GPR,
Rock fragments limit the effectiveness of conventional soil survey tools. GPR Application-- Soil Depth Determinations • 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.
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
The electrical conductivity of soils is influenced by: • the type and concentration of ions in solution. • the amount and type of clays in the soil matrix. • the volumetric water content. • the temperature and phase of the soil water. THE APPARENT CONDUCTIVITY OF SOILS WILL INCREASE WITH INCREASING: • Water • Clay • Soluble salt
EMI ApplicationHigh-Intensity Soil Surveys Identification and delineation of small inclusions of dissimilar soils within generalized soil polygons.
EMI Application Characterization of spatial soil variability EMI can provide a level of resolution not practical with traditional soil survey tools and methods
EMI Application Identifying soil-hydrologic-landscape units Menfro – Fine-silty, mixed, superactive, mesic Typic Hapludalfs
EMI Application Spatiotemporal variations in ECa associated with changes in soil moisture.