So many shells were fired that farmers are still digging up unexploded ones today. I saw a bunch of them at a corner of a farm field in Belgium pending pickup and it spooked me.
Yup, right there in the article vermontdevil linked to:
In the small farming towns of France and Belgium, undetonated World War I explosives that turn up during each year’s spring planting and autumn plowing are known as the “iron harvest."
https://www.washingtonpost.com/news/morning-mix/wp/2015/08/1...