The Iron Harvest is a term used to describe,
. . . the annual “harvest” of unexploded ordnance, barbed wire, shrapnel, bullets and congruent trench supports collected by Belgian and French farmers after plowing their fields. The harvest generally applies to the material from World War I, which is still found in large quantities across the former Western Front.
A 2016 Daily Telegraph article about unexploded munitions on the Somme noted that 25 tons of munitions had been removed from battlefields just in the first 6 months of 2016,
Michel Colling, head of the Amiens bomb disposal unit that handles the Somme, said: “Since the start of the year we’ve been called out 300 times to dispose of 25 tons of bombs.
“As soon as you start turning the earth up, you find them. At this rate, we have another 500 years to clear the area, so the work is far from over,” he told the Telegraph.
. . .
“We have accidents quite frequently. The rotor blades from tractors can set them off, though the farmers are generally protected as they are inside the vehicle and above ground.
“There are accidents with collectors who want to empty munitions either for their collections or to sell them.
“Also, when trenches are built on construction sites, these can set off devastating explosions. All the towns around here have been built on ground teeming with bombs.”
Articles on the Iron Harvest estimate that anywhere from 25 to 30 percent of shells fired in World War I failed to detonate. Add to that estimates that up to 1.5 billion shells were fired on the Western Front during the war, and it is no wonder that hundreds of tons of World War I era materiel is discovered every year in France and Belgium.