"Industrial farming based on huge amounts of cheap oil is not sustainable either. Think about all the oil/gas used in fertilizer production, pesticides, mechanization, harvesting, processing, storage, trucking, packaging."
Believe me, farmers think about that subject far more than you can imagine. They do everything they can to reduce the number of passes they have to make through each row of crops.
Farms like my in-laws leverage technology to the maximum. For example, they have GPS units on their tractors that are integrated with meters that track how much fertilizer is being distributed and they've been tracking this for almost a decade. When they harvest, they have GPS units on the combines and sensors that are tracking yields. At the end of every season they use 2D and sometimes 3D modeling to determine the optimum distribution of fertilizer down to a few feet. The off-season is dedicated to crunching these numbers, plus a mountain of other data that is collected. The goal is to absolutely maximize the efficiency of resource use: fuel, fertilizer, pesticides, etc.
When it comes to the question of sustainability you've got to remember that many if not most farms are generational. Fathers passed the farm to the current generation, they hope to pass it to their sons or daughters. They are far more invested in the economic and environmental sustainability of their operations than the folks that have made sustainability a trendy buzzword.
And understand that I am talking about industrial farms. There is no true distinction between the "industrial farm" and the "family farm." They are one and the same, but there is a lobby out there that has it out for agriculture. You sound like a real jerkoff if you're attacking the "family" farm, but if you use the word "industrial", you conjure images of smokestacks belching pollution and fat white guys in suits lighting Cubans with the money they stole from the pocket of the janitor. It's totally cool to attack those guys.
Think about it this way. Where I live it takes about 1,500 acres to support a family. Let's say you have three families working a farm, a father and his two married sons and their kids. That's three families that need about 4,500 acres to make a living. That is a lot of land and it requires an industrial, in the dictionary sense of the word, operation to farm.