Organic farming is sustainable farming?

It depends, on the practices being used. Sustainable farming is about being a steward to the land in which you practice agriculture on, in other words you protect that land from anything harmful and work to preserve a natural balance. Organic farming simply is a way of farming that is monitored by a governing agency (the USDA) which places restrictions on using certain chemicals in your growing operation. Organic operations still spray pesticides and insecticides as well as other cides contrary to popular belief. The reason they are allowed to is based on the USDA's definition of organic. If a toxic chemical is found in nature (i.e a plant) then it may be used in organic application despite the fact that is may pose ecological and health side effects. Organic farming that follows a pre 1980's philosophy is probably way closer to being considered sustainable than lets say that organic head of lettuce you have in your fridge. But all in all Organic and Sustainable farming are very different ways of farming, that can be interlinked but several key philosophies differ from one another