While I am not in Europe, we did research 20th century deep plowing techniques while investigating a circa AD 1100 Weeden Island site in Florida that had unusually deep (45 cm) plow scars. I also consult old agricultural journals and manufacturing catalogs to identify farm machinery parts recovered from sites. In addition, many of our historic Mississippi River and Red River navigation maps show what types of crops were growing in different fields along those rivers at the time. We sometimes use this in estimating depth of disturbance because different crops sometimes had different plowing techniques.