I know, right? And if you've got farmland you can't easily put plants on you can put animals on that instead, and eat the animals and use the stuff the animals leave behind to grow plants.

It's almost like an ecosystem that has worked for hundreds of thousands of years is actually a pretty solid idea.

Modern hydroponics are certainly not perpetual motion machines. The difference is that you can collect all of the unused nutrients below the plant and recycle them back into the input stream. Secondly, you can elevate the carbon dioxide levels because it's an enclosed system and encourage plants to grow faster. Finally, the enclosed nature more easily permits integrated pest management, which reduces total pesticide requirements...of course, herbicides are not required at all because of the way hydroponics grow.

It's not perfect, but it's exceptionally more productive than field agriculture.