One huge change in our lives was the Haber process, a way to generate fertilizer from air (and explosives as well). Before this, fertilizer was "harvested" from bird populated islands. The green revolution hinges on this change. Fertilizer is critical to farming (duh).
I've read concerns that we're using up sources of phosphorus readily available for use in fertilized. While not as critical as N, it's still needed by plants. Potassium is easier to come by.