Well, since 70s we learned a lot about the soil ecology. We can talk about N, which plant can't access directly. Roots have to produce different substances tha

Well, since 70s we learned a lot about the soil ecology. We can talk about N, which plant can't access directly. Roots have to produce different substances that are eaten by various organism in soil and they then break the N into form that could be accessed by plant. Commercial fertilisers give the plant N in form that could be consumed directly, so the plant is not motivated in producing compounds for rest of soil organisms. Once they are all dead the plant is reliant to those fertilisers. So this is, simplified version, of how plants gets N, but similar situations are with other compounds, especially K, which kinda change the structure of soil and basically lock it for other type of living organisms and nutrients.