You raise a good point. When I had an abandoned field reclaimed, the top layer of soil ended up in the pile with the stumps. The first plants which came in were Queen Anne's lace, daisies and black eyed Susans. These have big root clusters which started aerating the soil. Even the buckwheat and rye I planted came up anemic and didn't really do anything. Over time, grasses and weeds started coming in. A few years ago I realized that the wood in the stump piles had rotted down, so I'm gradually working that back into my garden. The entire 2 acre field has been taken over by grasses. This week I plan to turn it under, disc, and plant a cover crop of winter rye.Weeds are nature’s way of improving the soil. If you have more time than money let the weeds grow but mow the seed tops to reduce spreading. Mow high. Adding annual rye grass helps. As does light tilling.