Maybe to prevent them from digging up mines/artillery shells and blowing themselves up. My sister visited Verdun back in the '70s and was told farmers were still getting blown up when they'd hit a shell with their plows.
It would be neat to search for stuff like that, but IMO, far too risky.
The Annual Iron Harvest of Unexploded Shells from the WWI battlefieldsCan you imagine ONE TON per ten square feet and 2/3 is unexploded?
Nov 11, 2016. By Ian Harvey."According to some estimates, one ton of explosive material was fired for every square meter of the West French front’s territory. Two thirds of these explosives ended up un-detonated and laid there, later being buried in the chaos of the war."
"In Ypres alone, an estimated 300 MILLION explosives belonging to German and British forces were buried, most were duds and have not yet been discovered. As recently as 2013 a total of 160 tons of munitions, including 15-inch naval gun shells, were meticulously unearthed from the regions around Ypres.