<Looks outside at corn field
Well, they could use a little more ammonium phosphate on the field as a few spots are suffering nitrogen starvation, but another field owned by another farmer is doing just fine down the road.
My own garden did okay, given it used to be a burn pile for previous owners and I need to do some more prep work.
The reality is that carbon dioxide is plant food that is desperately needed - plants are currently operating in CO2 starvation mode.
You want to know what killed the dinosaus? The drop in CO2.
Human mining operations have been reclaiming carbon and other nutrient compounds locked in the crust, away from biological cycles, and returning them to that cycle.
So, with respect to the man's work, sometimes one can focus a lot of effort on case studies which, while supporting their theory, are exceptions to the greater trend.
Many of the places we turned into farm land were flooded river deltas and irrigated deserts. The decline in soil quality has more to do with the increased water usage of urban populations and the competition for water sources in arid regions (which includes California) rather than a systemic global problem.