Compost.

Compost makes up the major addition to our gardens fertility every year. The majority of that is in the form of aged chicken litter. You see I try and get the most out of everything we buy in and that includes the chicken feed as well. We mostly try to litter our chickens on cut and dried grass clippings but in the winter when they are not outside as much we need to supplement their litter with wood bedding. Usually two to three times a year I clean out the coop and drag the litter out behind the pole barn. Once it is out there I basically leave it to mellow for at least a year and sometimes two. I also add to the compost in and effort to increase the nutritional components. My main additions are charred wood, ash and burned bone.
We have a number of mature trees on our property and that means plenty of sticks for the burn barrel. I used to make charcoal just for the forge but now I make it for the garden as well. I ran across an article on Terra Preta some time ago and ever since I try to add charcoal to my soil when I have a surplus.
I also used that same burn barrel a few years back to dispose of several deer carcasses left over from deer hunting. I burned most of the deer bones by suspending them over the fire which was stoked by the fat from the bones and also some that was left over from the butchering. Afterwords I had an ash that was rich with bone fragments and I figured that would add more nutrients to the pile so I saved the ash and bone to add to the pile.
I also add leaves in the fall to the base of a new pile. Sometimes I also add coffee grounds as well to offset the alkaline nature of the wood ash. That is all. If I get a chance I may turn the pile once or twice a year but that is about it.
In addition to this I also keep a garden compost pile that gets most of the organic matter from the kitchen.

In unrelated news I made a batch of strawberry rhubarb jam this evening and this weekend I dried a ton of dill.