General:
* Impoverish: This is the most direct opposite, meaning to make poor or less wealthy.
* Deprive: To take away something valuable or necessary.
* Exhaust: To use up all of something, leaving it empty or depleted.
* Deplete: To reduce the amount of something, often to a dangerously low level.
* Diminish: To make something smaller or less important.
In specific contexts:
* For soil: Exhaust or deplete are good choices, referring to removing nutrients.
* For knowledge: Ignorance or uninform could be used.
* For experience: Limit or restrict might be suitable.
The best antonym will depend on the specific situation and the way "enrich" is being used.