Measuring and mapping subsurface soil elemental distribution using neutron-gamma analysis

Authors: Yakubova, Galina; Kavetskiy, Aleksandr; Prior, Stephen - Steve; Torbert, Henry - Allen

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 2/17/2023
Publication Date: 9/15/2023
Citation: Yakubova, G.N., Kavetskiy, A.G., Prior, S.A., Torbert III, H.A. 2023. Measuring and mapping subsurface soil elemental distribution using neutron-gamma analysis [abstract]. 2nd Global Summit on Earth Science and Climate Change (Adv. ESCC 2023), London, UK, September 14-15, 2023.

Interpretive Summary:

Technical Abstract: Due to potential effects on climate change, assessing impacts of modern agricultural practices on soil carbon sequestration requires exact knowledge of critical elemental content (primarily carbon) over large soil surface areas (several hectares). Collecting and processing representative field soil cores for traditional laboratory chemical analysis is labor intensive and time consuming. Our neutron-stimulated gamma analysis system (paired with GPS) is a good alternative to the traditional soil elemental method. Neutron-stimulated gamma analysis can be used for simultaneous in-situ measurements of primary elements (e.g., C, Si, O, H, Fe, and K) in agricultural soils. Neutron-gamma analysis is based on detecting gamma lines that appear due to neutron nuclei interactions. Many nuclei can be detected and quantified by the presence of their characteristic gamma lines. State-of-the-art nuclear physics methodologies and instrumentation, combined with commercial availability of portable pulse neutron generators, high-efficiency gamma detectors, reliable electronics, and measurement and data processing software, have currently made the application of neutron-gamma analysis possible for routine measurements in various fields of study. Long-range trends of changing elemental content are of interest when mapping soil elemental distribution for agricultural purposes. Elemental distribution can be represented as isolines overlaying a geographical map of a studied field. Data suitable for mapping should be prepared as datasets of geographical coordinates and corresponding elemental contents. Isolines across the field can be created from such datasets by different methods (e.g., kriging, local polynomial interpolation) using available software (e.g., ArcMap). All steps required for creating soil elemental distribution maps will be presented on the poster in more detail. This will include the scheme and cart design for neutron gamma analysis, means of primary data processing and converting acquired gamma signals to elemental content, and field surveying methodology for map creation. Example elemental (primarily carbon) maps of real agricultural fields suitable for use for both assessing agricultural practices and for the carbon credit market will also be discussed.