Not All crops deplete the soil.  Legume plants self fertilize, These include alfalfa, peas, soybean, and may others. Unfortunately the majority of crops planted (grains, corn, etc) require fertializer inputs. Prior to the use of chemical fertilizers, farmers rotated fields, where one or two fields might contain a harvestable crop and the remained where planted with grasses to revitailize the field. However, this is less productive because it requires about 4 times the land for same amount of crops produced. With the Green revolution (chemical fertializers) the same farmer could produce crops on all of his land.

Now the problem is reversing that process is going to be very difficult. In order to go back to the old system, farmers will need to aquired 150% more land than they currently own, or we need to shrink the population by 75%.

Although I suspect that we would not need to go all the way back if we plant a mix of Legumes and grains on the same fields (at the same time) and scale back fertilizer use. Perhaps we can get by with only increasing the farm land use by 30% to 50% (guestimate) and by curbing wasted food.