Book excerpt: Modern industrial agriculture is not sustainable because of its heavy reliance on petroleum, a non-renewable source of the energy used in farming, and because of pollution caused by petroleum products such as fertilizers and pesticides. A systems analysis of farming suggests that agriculture will be more sustainable when services of nature, such as nutrient recycling by soil micro-organisms and natural controls of insects, replace the services now provided by energy from petroleum. Examples are drawn from the Southeastern USA, but lessons learned can be applied worldwide.