[bluGill]

When you pull a potato off a field, you're taking with it a bunch of phosphorus. That is why we have to have a replacement for that. I'm not sure how to solve the problem long term. I agree. Morocco wasn't the right answer, but what is?

[jijijijij]

The solution is easy: Recycle poop and pee. All that sweet nitrogen and phosphorous that has been DNA, ATP and protein is right there in the bowl. The problem is humans flushing all the good stuff down the toilet and into the ocean. With today's knowledge, using human excrement as fertilizer can be done safely. At least recover the phosphorous.

[bluGill]

Not as easy as you say, but the idea is sound enough