Gamma‐ray spectrometry as versatile tool in soil science: A critical review

Abstract

Gamma‐ray spectrometry is an established method in geo‐sciences. This article gives an overview on fundamentals of gamma‐ray spectrometry that are relevant to soil science including basic technical aspects, and discusses influencing factors, inconsistencies, limitations, and open questions related to the method. Gamma‐ray spectrometry relies on counting gamma quanta during radionuclide decay of 40K, 238U, and 232Th, but secular equilibrium for the decay series of U and Th must be given as decays of their respective daughter radionuclides are used for determination. Secular equilibrium for U and Th decay series, however, is not always given leading to, e.g., anomalies in U concentration measurements. For soil science, gamma‐ray spectrometry is of specific value since it does not only detect a signal from the landscape surface, but integrates information over a certain volume. Besides, different spatial scales can be covered using either ground‐based or airborne sensing techniques. Together with other remote sensing methods, gamma signatures can provide completive information for understanding land forming processes and soil properties distributions. At first, signals depend on bedrock composition. The signals are in second order altered by weathering processes leading to more interpretation opportunities and challenges. Due to their physico‐chemical properties, radionuclides behave differently in soils and their properties can be distinguished via the resulting signatures. Hence, gamma signatures of soils are specific for local environments. Processes like soil erosion can superimpose gamma signals from in situ weathering. Soil mappings, available K and texture determination, or peat and soil erosion mapping are possible applications being discussed in this review.

Groundcover Mulching in Mediterranean Vineyards Improves Soil Chemical, Physical and Biological Health Already in the Short Term

“…Passive gammaray spectrometers measure the natural emission of gamma-rays from the topsoil (first 30-40 cm), in particular the emission of the radionuclides 40 K, 232 Th, 238 U. The radionuclides content of the soil is strongly related to soil parent material mineralogy and to several soil physical and chemical characteristics, namely texture, calcium carbonate content and stoniness [46,47]. Despite their large potential, ECa and gamma-ray have been used merely as a mapping tool [48][49][50], while, to the best of our knowledge, they have never been used to improve the assessment of soil management and other agronomic practices in vineyards.…”

A new methodological framework for geophysical sensor combinations associated with machine learning algorithms to understand soil attributes

“…However, new geotechnologies have emerged in recent decades, allowing the acquisition of data at shorter times, with non-invasive and accurate methods such as reflectance spectroscopy, satellite imagery, and geophysical techniques Demattê et al, 2017Demattê et al, , 2007Fioriob, 2013;Fongaro et al, 2018;Mello et al, 2021;Terra et al, 2018). Among these technologies, geophysical sensors have been recently used in pedology to understand pedogenesis and the relationship between these processes and soil attributes (Son et al, 2010;Schuler et al, 2011;Beamish, 2013;McFadden and Scott, 2013;Sarmast et al, 2017;Reinhardt and Herrmann, 2019). Among these geophysical techniques used, we highlight gamma-ray spectrometry, magnetic susceptibility (κ), and apparent electrical conductivity (ECa).…”

“…Weathering and pedogenesis, concomitantly with the geochemical behavior of each radionuclide, determine their distribution and concentration in the pedosphere (Dickson and Scott, 1997;Wilford and Minty, 2006;Mello et al, 2021). Therefore, gamma-ray spectrometry can provide important information for the comprehension of soil processes and attributes (Reinhardt and Herrmann, 2019), soil texture (Taylor et al, 2018), mineralogy (Wilford and Minty 2006;Barbuena et al 2013), pH (Wong and Harper, 1999), and organic carbon (Priori et al, 2016).…”

Proximal Mobile Gamma Spectrometry as Tool for Precision Farming and Field Experimentation

“…In the past years, soil scientists have made increasing efforts to evaluate possibilities related to gamma spectrometry and to overcome limitations for practical applications. Proximally recorded gamma spectra provide information on soil properties that are potentially relevant for different applications in agricultural soil use and research [1][2][3].…”