

No, my point is that auto liability insurance covers the people you hurt while driving. It does not cover yourself or your own car, and it’s perfectly legal not to insure your own car against your own negligence, even when it’s required to insure everyone else’s property against your own negligence.
The thing being insured is different, so an auto liability insurance mandate is fundamentally different from a health insurance mandate for oneself.
Yes, “green manure” is taking nitrogen fixing crops (like clover and beans and peanuts) and to mulch them while still green, and incorporate that decomposing mulch into the soil you’re using. That adds nitrogen in fewer steps than the traditional way of using animal manure (where the nitrogen still ultimately comes from plants).
Of course, the modern Haber process also fixes nitrogen through industrial chemistry rather than agriculture, so most commercial fertilizer today gets its nitrogen from chemical synthesis of atmospheric nitrogen into ammonia.