Here's an article that may prove helpful: weight of soil
If you use the general estimate that the top 6.7 inches of good, loamy soil is 2M lbs, one acre inch weighs roughly 300,000 lbs. with roughly 39 inches in a meter, you would need 11,700,000 lbs of biomatter to create an acre meter of soil. I'llleave it to you to do the heavy lifting with a really big wheelbarrow,
and to convert to metric since I don't know if Italians even think in acres.
All the above is subject to so many variables in the types of materials, water content, decay rates, etc, that it is probably meaningless except to show that it takes a HUGE amount of material.