Nash Huber was born and raised in south-central Illinois, where small family farms were growing corn, soybeans and oats, along with wheat. They grew these crops for cash sales and for animal feed, since they all had some cattle, dairy cows, hogs and chickens. No one was thinking about farming "sustainably" in those days. They were farming the way their ancestors had farmed. It turns out that their farms were far more sustainable than the industrial agriculture that has succeeded them.
Organic does not equate to sustainable as long as organic farmers model their farms on conventional agriculture. Even Monsanto calls itself "sustainable!" In order to be truly sustainable, we cannot expect to build a cash economy out of natural systems.
In the future ALL farming will have to be organic because society will get to a point where it cannot tolerate paying for the high environmental costs of conventional agriculture. But that, in and of itself, does not make organic agriculture sustainable because it generally uses the same techniques as conventional agriculture. It’s a lot less harmful, but still not sustainable.
A true sustainable system will always mimic nature. Nature hates bare ground and as soon as there is a disturbance that causes bare ground, like a landslide, fire, plow, or bulldozer, nature wants to cover it with plants. These plants (we might call them weeds) start to form new topsoil. They fix nitrogen, hold moisture, and create a structure for living organisms to repopulate the soil.
Humans, however, want specific plants to grow and not have to compete with the weeds. We use machines, chemicals, or manual labor to keep the weeds at bay, to the point that we create bare ground between the rows. Even on the best organic farms, where we work hard to maintain soil health, we expose some of the ground to water erosion, sun bleaching, wind, etc. Given enough time, the soil will collapse. In conventional agriculture that time is short. Organic farming greatly increases that time, but we still can do better.
A time-honored technique to increase sustainability is to put animals, especially cattle, on the land (in temperate, not tropical climates, where the soil is very different). Cattle and grass have a special relationship in the northern hemisphere. Cows do not eat grass to the ground; they munch the tops of the grass as they walk along. This causes part of the grass’s root system to die off and decay into soil while the rest of the roots push up more grass to collect sunlight. Meanwhile the cattle are fertilizing the soil as they walk about. Putting cattle on soil for one or two seasons every five years is an easy and efficient way to sustain soil health, and one that was perfected by Mother Nature on the Asian taiga, the North American prairie or the plains of Serengeti many millennia ago.