At the local earthworm farm, Im sure everyone here knows earthworms are the superstars of soil building, the nearby dairy hauls in truckloads of cow manure. Heaping it into a few rows threefeet wide by two feet feet high and mabey 50 yards long, (they are under shed like roofs), the earthworms are allowed to do their stuff. There are no flies, no smell, quite surprizing untill you think about the origens of this system. Every few days or week or so they put the mix thru a seperator and put the worms back onto a new batch of manure. The castings are sold for renewing and assisting soil health.
I read some years ago how we could spend as a country a small fraction of money and redo all the depleted farmland in a number of years to a richness unknown for years.