Soil erosion is a global threat. Each year 75 billion tons of fertile soil is lost from world agricultural systems. The magnitude and rate of soil erosion can be determined through gamma spectrometry by comparing the content of the radionuclide caesium-137 in eroding or depositing sites with the caesium-137 content at undisturbed stable areas. If the content is lower than that of the reference site, soil has been lost to erosion - if it is higher soil has been deposited.