Soil Nutrients: Deficiency and Replenishing
It’s true that plants grow from the top-down. In other words, it uses water and carbon dioxide from the air to grow.
But nutrients like nitrogen (N), phosphorus (P) and potassium (K) are key elements for plant growth. If you deplete the soil from these nutrients, this deprives the plants from growing.
For example, this is an ongoing problem for farming and tree harvesting areas. This is why farmers rotate crops and allow periods of rest or “fallow” to replenish soil with nutrients.
In addition, farmers use chemical and natural fertilizers to replace nitrogen which are leached from the soil by growing plants or runoff into streams.