Speaker
Description
South Africa faces a critical deficit in spatially continuous, cost-effective soil health monitoring, a gap that undermines informed land management, food security planning, and national resource governance. Conventional soil assessment methods, which depend on discrete point sampling and laboratory analysis, are inherently too slow, too costly, and too spatially limited to capture the landscape-scale variability that characterises the country's diverse agricultural terrain. This study addresses that deficit by investigating the utility of natural gamma radiation as a rapid, non-invasive proxy for soil health indicators at Groote Post Wine Estate, Darling Hills, Western Cape (33°22'S, 18°35'E), and by evaluating the scalability of this methodology as a national resource intelligence tool.
Groote Post Farm (approximately 2,700 ha) occupies a geologically complex terrain defined by the interaction of three lithological units: the Neoproterozoic Malmesbury Group metasediments, the Cape Granite Suite plutons (emplaced approximately 550–510 Ma), and Quaternary aeolian sands and calcretes. Each unit exhibits a characteristically distinct naturally occurring radionuclide (NOR) signature. The Cape Granite Suite, on which the estate's vineyard is situated, is among the most radiogenic of common rock types, with reference activity concentrations of approximately 74.1 Bq/kg for uranium (²³⁸U), 1232.2 Bq/kg for potassium (⁴⁰K), and 84.6 Bq/kg for thorium (²³²Th). The Malmesbury Group metasediments exhibit moderate concentrations, while the Quaternary deposits are geochemically dilute. This natural radiometric contrast makes the site an ideal natural laboratory for testing gamma-based soil mapping.
The study employs a multi-phase methodology. Phase 1 involves a UAV-borne gamma radiation survey using a DJI Matrice 350 RTK platform equipped with a NaI(Tl) scintillation detector. The UAV operates at a controlled altitude of approximately 10 m above ground level at a lateral speed of 5 m/s, acquiring a continuous, georeferenced gamma radiation dataset with a detector footprint of approximately 14 m in width. Concurrent ground-based soil sampling is conducted systematically across the vineyard to a depth of 30 cm, with four samples per row and a row-skipping interval of approximately five rows to balance spatial representativity with operational efficiency. Phase 2 involves spectral analysis of the gamma radiation data using both Window Analysis (WA), which isolates specific energy windows corresponding to ⁴⁰K (1.46 MeV), ²³⁸U (1.76 MeV), and ²³²Th (2.61 MeV), and Full Spectrum Analysis (FSA), which utilises the entire gamma energy spectrum to account for spectral overlap and background radiation, yielding more accurate radionuclide concentration estimates. Statistical correlation analysis using both Pearson (r) and Spearman (ρ) coefficients will evaluate the relationships between gamma-derived variables and measured soil health indicators including pH, total carbon, clay content, and bulk density. Radionuclide ratios — specifically Th/U, U/K, and Th/K — will be calculated as geochemical proxies for weathering intensity, mineral composition, and soil texture respectively. Phase 3 applies Geographic Information Systems (GIS) spatial interpolation techniques, including Inverse Distance Weighting (IDW) and Kriging, within QGIS to generate high-resolution, continuous spatial distribution maps of radionuclide concentrations, derived ratios, and soil health indicator surfaces across the study area.
This research is expected to generate the first quantitative NOR dataset for the Malmesbury–Cape Granite Suite contact zone of the Darling Hills, filling a fundamental scientific gap in South African geoscience. If validated, gamma-ray spectrometry as a soil health proxy offers a cost-effective and scalable alternative to conventional monitoring, with direct application to precision agriculture, environmental baseline establishment, and national resource planning. The national security dimension of the study is grounded in South Africa's formal recognition of food security as a core component of national stability, as articulated in the White Paper on National Defence (1996) and the National Development Plan 2030. By repurposing radiometric techniques — originally developed for military reconnaissance and nuclear safeguards — as a soil intelligence tool, this research demonstrates the dual-use potential of geophysical sensing for strategic resource security. The methodology is scalable from farm level to landscape and regional scale, with potential for adaptation to broader SANDF and SSA environmental monitoring frameworks.
Keywords: natural gamma radiation, soil health, NaI(Tl) spectrometry, UAV-borne radiometry, Groote Post Farm, Cape Granite Suite, Malmesbury Group, GIS spatial mapping, Kriging interpolation, national security, food security, precision agriculture.
| Apply for student award at which level: | MSc |
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| Consent on use of personal information: Abstract Submission | Yes, I ACCEPT |