If the manure is 30 years old it won't have any living seeds in it. 30 year old manure that hasn't be rained on is like gold to a garden.
Mow the area and the surrounding area low. Make sure your tiller has a adjusted working slip clutch if its so equipped. Till shallow over the mown area, maybe two inches deep. Let sit a day or two. Pick up rocks. Till again. Soil test as FWJ said to do. Add anything that is needed. Pick up the rocks you can find. Wait till there is moisture in the soil ( you can water it) and till in as much of that 30 year old manure as you can haul to it. Pick up rocks. Plant a cover crop this fall such as annual rye. Add more manure next spring and till it all in deep. Pick up rocks. You now have a garden.
Mow the area and the surrounding area low. Make sure your tiller has a adjusted working slip clutch if its so equipped. Till shallow over the mown area, maybe two inches deep. Let sit a day or two. Pick up rocks. Till again. Soil test as FWJ said to do. Add anything that is needed. Pick up the rocks you can find. Wait till there is moisture in the soil ( you can water it) and till in as much of that 30 year old manure as you can haul to it. Pick up rocks. Plant a cover crop this fall such as annual rye. Add more manure next spring and till it all in deep. Pick up rocks. You now have a garden.