Our area was a traditionally fertile area for agriculture. Receding glaciers left behind tons of sediment. Black dirt was 4 feet deep in my backyard; a sewer replacement trench let me scope that measurement..
In 2010, the yard was ripped up by a backhoe for a sewer line replacement ($4000 ouch!), it needed some serious attention this past spring. Ceramic sewer was scattered everywhere and lots of gravel and other stuff was brought up from the backhoe work. With help, we unloaded 8 full-size pick-up truck loads of municipal compost (leaves, branches, bits of plastic) from our local city DPW and raised the yard about 2 inches, for nice drainage.
After several rototilling sessions to mix in the compost, we planted mostly from seed. I would guess that our soil is pretty rich with high levels of humus. I haven't tested it's pH or had nutrient levels tested, but we've had great success with our garden thus far.
After this year, we will begin incorporating compost with chicken droppings and household compost, as well as yard waste as raised bed dressing. We've never used any pesticides, insecticides, or artificial fertilizers on the garden. We don't plan to, but it is clear that the previous owner did apply pesticides, herbicides, and fertilizers.
Watering may be required, but not regularly. In summer 2010, the garden was watered often after initially sewing seed in the second week of May, but by mid-June, the watering stopped; none since, either. I hadn't been very proactive with mulches last year, so that may be a serious way of reducing the overall water cost of the project.