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 t

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.