The soil pH is measured using the following treatments: 1:1 H2O, 1:2 0.01 M CaCL2, and 1 N KCl. See the Soil Survey Field and Lab Methods Manual for details. To read more about the different reaction pH tests, see USDA survey technical note here.
Saturated paste pH and Extract. See pages 211-212 of the Soil Survey Field and Lab Methods Manual to learn about the utility of paste pH as an indicator of dissolved CO2, moisture content, EC composition, soluble salt composition and concentration, presence and amount of gypsum and alkaline-earth carbonates.
Below is a snapshot of the NRCS manual showing "rules of thumb" from saturated paste pH measurements (adapted from U.S. Salinity Laboratory Staff, 1954).
Estimations of total organic matter content can be made using loss-on-ignition methods.
Loss on ignition following Nelson and Sommers (1996).
Loss on ignition for preparing samples for submission to PSU AMS facility. This document also includes methods on acid washing samples to remove carbonates.
Whole-soil geochemical methods include X-ray Fluorescence (XRF) and Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) and ICP-Mass Spectrometry (ICP-MS).
portable X-ray Fluorescence (p-XRF)
Soil geochemistry can be evaluated using p-XRF in Smith 306. It is recommended that samples be air-dried, powdered and hydraulically pressed into pellet form. The lab contains a suite of external certified reference materials in pressed pellet form. See the GeoREM website for elemental concentrations of certified reference materials (Jochum et al., 2005).
The following are useful references when designing a p-XRF experiment:
Additional resources for applying p-XRF and interpreting X-ray spectra:
Inductively Coupled Plasma Spectroscopy
Geochemical characterization of major, trace and rare earth elements is conducted using lithium borate fusion and ICP-AES and -MS. A four-acid digestion combined with ICP-AES is used to quantify base metal (Ag, As, Cd, Co, Cu, Li, Mo, Ni, Pb, Sc, Tl and Zn) concentrations.
Extractable elements are characterized using Mehlich-3 extraction (Mehlich, 1984). See University of Kentucky soil lab for methods and costs.
References
Gill, R., 2014. Modern Analytical Geochemistry: an introduction to quantitative chemical analysis techniques for Earth, environmental and materials scientists. Routledge.
Jochum, K.P., Nohl, U., Herwig, K., Lammel, E., Stoll, B. and Hofmann, A.W., 2005. GeoReM: a new geochemical database for reference materials and isotopic standards. Geostandards and Geoanalytical Research, 29(3), pp.333-338.
Mehlich, A., 1984. Mehlich 3 soil test extractant: A modification of Mehlich 2 extractant. Communications in soil science and plant analysis, 15(12), pp.1409-1416.
Richards, L.A., 1954. Diagnosis and improving of saline and alkaline soils. US, Salinity Laboratory Staff. Agric. Handbook, (60).
Sherrod, L.A., Dunn, G., Peterson, G.A. and Kolberg, R.L., 2002. Inorganic carbon analysis by modified pressure-calcimeter method. Soil Science Society of America Journal, 66(1), pp.299-305.
Soil Survey Staff. 2009. Soil Survey Field and Laboratory Methods Manual. Soil Survey Investigations Report No. 51, Version 1.0. R. Burt (ed.). U.S. Department of Agriculture, Natural Resources Conservation Service.
Soil Survey Staff. 2014. Kellogg Soil Survey Laboratory Methods Manual. Soil Survey Investigations Report No. 42, Version 5.0. R. Burt and Soil Survey Staff (ed.). U.S. Department of Agriculture, Natural Resources Conservation Service.
The pO2, pCO2 and pCH4 from soil are measured using a field-portable gas analyzer. Our gas analyzer system was designed using Brecheisen et al. (2019) model and is shown below. Note annotation on right image. Red numbers refer to three-way valves.
Apogee O2 sensor readout: % by vol.
Vaisala GMP251 CO2 sensor readout: mV (V)
Useful conversions: 1V = 2 x CO2 % (e.g., 19 mV = 0.038 % by vol. CO2)
We are working towards onboarding a methane sensor to the system.
References
Brecheisen ZS, Cook CW, Heine PR, Ryang J, Richter Dd (2019) Development and deployment of a field-portable soil O2 and CO2 gas analyzer and sampler. PLOS ONE 14(8): e0220176. https://doi.org/10.1371/journal.pone.0220176