You are getting into territory where there isn't a consensus on whether it's "vegan" or not. The surface area of vegan practices is large and complex, and only certain core principles are shared by virtually all vegans. You probably won't find a lot of agreement from most vegans with your statement. Even organicly grown food uses organic pesticides, which could arguably be called not vegan due to killing insects. And there is organic meat after all.

A certain percentage of soil is made up of decomposed animals, so anything grown is not vegan by some arbitrarily strung out standard. Where do you draw the line?