I am aware that gardening is possible without gas or petroleum products. Are you saying there's a fertilizer available that is natural and doesn't contain animals or animal products in it? Check again. maybe I'm wrong but most organic fertilizers are, largely, manure (chicken manure mostly--it's crazy with nitrogen). Here on the tiny homestead we fertilize using crop rotation, legumes, mixed cover crops, and composted (mostly vegetarian) kitchen waste, as well as our beloved chicken manure and dry waste mucked out from the chicken coop.

Anyway, I don't wanna argue the nuances of what's available at the garden store. I'm talking about food production on a society-wide scale. We agree that treading lightly is a good idea, and we are all finding our ways to do it. I think that's the most important thing.

The production of food and its relationship to soil fertility is of great spiritual and practical importance to me. I could talk about it forever, in case that's not painfully obvious; but I shall leave it at that, and close by offering some more specific recommendations from my earlier rant, for anyone who may be interested in learning more about traditional food production, petroleum usage in agriculture, and the way it relates to our society.

Wendell Berry "The Unsettling of America" Sierra Club Books, 1977
James Howard Kunstler "The Long Emergency" Atlantic Monthly Press, 2005
Richard Manning "The Oil We Eat," originally an article in Harper's: http://www.wesjones.com/oilweeat.htm
A very enriching discussion of community production hidden in a recipe for ginger beer: http://www.westonaprice.org/foodfeatures/Realthing.html
An eye-opening treatise on the need for animal fertility in vegetable farming: http://www.westonaprice.org/farming/wasteland.html