How does soil regain its fertility?

Some soils gradually regain fertility as soil minerals continue to break down, releasing plant nutrients like calcium, magnesium, iron, potassium, etc.

Soils also regain fertility with time as plants live, grow, die and then decompose on and in the soil. Humans can help this along by adding organic materials, like compost and manure. Organic matter includes plant nutrients that include nitrogen, phosphorus, sulfur, magnesium, etc.

Direct additions of chemical fertilizers will also increase a soil's fertility, of course.