How much does the moisture in the ground have to do with detection depth?
Moisture in the ground by itself has very little affect on the operation of a metal detector. Fresh water, such as rain or irrigation, is not much more conductive than the dirt it soaks into. Most metallic items in moist soil will start to corrode. As these items start to break down, they create a halo of super mineralized soil around the target. The halo effect makes the target appear bigger to the metal detector. Iron and other ferrous targets will corrode faster than other targets. Gold does not corrode, and silver, copper, and brass corrode more slowly than iron. So, while the halo effect will work on some targets, it will not work on all.
