Population control is the key factor here, because for organic methods
to be truly sustainable, one needs animal manure and animals need water
and space, too. It's all very cyclic.
We humans are a problem and capable of a solution to the challenge of
the sustainability of Earth's systems. Humans adjust quickly to food
supply. Once we have more than we need we produce lots more of us.
Lots more of us require ever more more food. The article correctly
notes that without artificial nitrogen there could be far fewer
humans. But like villages that strive to become towns that strive to
become cities that strive to become ever bigger, it seems more is a
basic, or base, human instinct.