Submitted to: Vadose Zone Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/21/2015
Publication Date: 2/1/2016
Publication URL: http://handle.nal.usda.gov/10113/5430223
Citation: Yakubova, G.N., Kavetskiy, A.G., Prior, S.A., Torbert III, H.A. 2016. Benchmarking the inelastic neutron scattering soil carbon method. Vadose Zone Journal. 15(2). doi:10.2136/vzj2015.04.0056.
Interpretive Summary: Carbon transfer from the atmosphere by plant growth may help mitigate global change through soil carbon storage. To identify best soil management practices that maintain good soil carbon levels require accurate and rapid monitoring. Soil carbon was measured with a novel device called a mobile inelastic neutron scattering system and compared to the standard dry combustion method. This system required no core sampling and the measured (for 1 h) soil carbon accuracy was comparable to the standard method for assessing soil carbon in the upper soil profile.
Technical Abstract: The herein described inelastic neutron scattering (INS) method of measuring soil carbon was based on a new procedure for extracting the net carbon signal (NCS) from the measured gamma spectra and determination of the average carbon weight percent (AvgCw%) in the upper soil layer (~8 cm). The NCS extraction utilized the net INS spectrum which was the difference between the INS and TNC (thermal neutron capture) spectra and the net-INS system background spectrum. The proportionality between NCS and AvgCw% at any soil carbon depth distribution was demonstrated. The theoretical model for NCS calculations for soils with different carbon depth distributions accounted for neutron and gamma ray propagation laws in our analysis; previous model results were verified by comparison to a Monte Carlo simulation using Geant4. The experimental results confirmed the identified proportionality. Calibration of the mobile INS system using pits filled with synthetic soil is described; this calibration was used for AvgCw% determinations in INS field measurements. The calculations of AvgCw% in the upper soil layer (~8 cm) and corresponding standard deviations were determined using carbon dry combustion measurements. Benchmarking soil carbon determination by INS demonstrated results comparable to the standard dry combustion technique (DCT). Given the agreement between these methods, the described INS measurement system can be recommended as a reliable alternative means of measuring soil carbon.