Organic agriculture is actually quite sustainable, and when intensively cultivated, very productive. Its all a matter of how you do it. For example, the Iroquois nation utilized the 3 sisters system where they grew corn, squash and beans. Beans fixed nitrogen in the soil, corn provided a pole for the beans to grow and the squash acted as a natural mulch. This allowed the Iroquois to develop a sedentary, high pop density, essentially anarchist/communist society. Small scale, organic plots can provide enough food. However I'm more in favor of high rise vertical farms for most communities. You can still utilize organic methods, but it would provide yields far higher than solely ground based farming.