Measuring and Mapping Potassium in Agricultural Fields Using Gamma Spectroscopy

Mapping total soil potassium based on scanning gamma spectroscopy, paired with global positioning system (GPS) technology is described. Total potassium was determined from the 1.46 MeV gamma peak area of the 40 K isotope. A calibration coefficient was defined based on measuring spectra of small reference samples (dozen of cubic decimeters) and Monte Carlo simulations (Geant4) of spectra in different sample volumes (up to several hundred cubic meters). Soil potassium distribution maps of agricultural fields were created based on measuring the potassium-40 peak areas in gamma spectra and calculating the soil potassium weight percent using defined calibration coefficient. ArcMap software was used for map creation. Results demonstrated the feasibility of using gamma spectroscopy and the described calibration method for determining total soil potassium.