system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How is the soil replenished in farming fields.

I am wondering how the soil remains at a constant level in industrially farmed fields. I understand that a plant is growing into a big plant with crops. The matter that the plant consists of comes from the soil. When parts of these plants are removed for usage, that implies a matter deficit in this field. So, isn't the field supposed to recede with every harvest?

PS: I recently became a father and I took up gardening as a hobby, so that I have something that I can do with my kids. We are doing pretty well farming avocado seeds and lentil sprouts :)
gpt
> The matter that the plant consists of comes from the soil.

**No it doesn't!** The matter which makes up the vast majority of the plant comes from the *air*. Carbon is extracted from CO2 and used to create things like sugars and fibers which make up the plant. If you carefully grow a plant inside a pot of dirt then you will see the pot steadily becoming heavier as mass is collected and added to the plant. Fertilizers can aid the growth of plants but it is not the source of the bulk of the material which they contain.