[ArchD]

If the concern is minerals, aren't there rocks in the soil that as they get broken down over time will release minerals?

As for non-mineral things like nitrogen, isn't the soil supposed to have an ecosystem that replenishes these things? In healthy soil, there are bacteria, fungus, earthworms, ants etc to make the soil conducive for plant growth.

Nature doesn't add artificial chemicals for fertilizer yet left to its own devices, plants thrive in natural soil. The activity of growing plants per se doesn't deplete soil. Maybe it's the use of pesticides and herbicides that kills the soil by killing the things living in it.

[bluGill]

> As for non-mineral things like nitrogen, isn't the soil supposed to have an ecosystem that replenishes these things?

Iowa farmers grow corn for money, and Soybeans to replenish the nitrogen. They have discovered enough uses for the "waste" soybeans that sometimes it is worth more than corn, but the original reason soybeans were planted was for the cheap nitrogen.

[Retric]

In nature biomass ends up in roughly the same places so this balances out, with crops farmers are removing significant biomass from farmland. The use of fertilizer is in part a consequence of specific plants depleting soil.

Carbon, nitrogen, oxygen, and hydrogen which represents the bulk of organic mater is available from air and water, but phosphorus for example gets depleted. Nitrogen fertilizer is something of a special case as extracting it from the atmosphere takes a lot of energy. However, nitrogen fixing bacteria will return it to soil if given time to do so.

The specifics of course get more complicated, sod for example is physically removing layers of soil.