In this case, the “weak links” are soil and oil. In the past, these have been cheap — when land was degraded, folks bought more or pumped in more NPK.

Now some people are realizing that at some point, there’ll just be no more virgin soil or cheap land to be had and that it’d make sense to come up with some alternatives.

One idea is to substitute labor and education for those nonrenewable inputs — many sustainable farming techniques can produce food more efficiently as measured by inputs and land used, but generally they’re a lot of work — think farmer digging instead of tearing up the land with a tractor.