The ground that you are talking about is experiencing a nutrient over load. You'll need to increase the carbon content of the ground so that composting can take place and the nutrients made available. The composting will go a LONG WAY towards reducing the smells that you mentioned.
You'll need to incorporate high carbon organic materials into the soil and then let the ground go fallow for a season. Cover the ground with large portions of Wood Shavings, Leaf Litter, Straw or Lawn Clippings, then rototill the material into the ground. Another source would be to run a bunch of tree pruning material through a wood chipper...its bulky, but with a high nutrient load it should break down well. It will probably take a lot of material to offset the nutrient load, a soil test would give you a better idea of how much material you'll need to incorporate. Ask for a recommendation with the soil test...
Once everything is rototilled into the ground then water the area and let it sit for the summer. Next spring you should have a nice rich soil...great, awesome garden soil...and NO smell.