-Build a
compost heap on the spot
Over time, any leachate from the heap will add fertility to the spot. As the heap is turned, soil and compost will be blended. When the compost is ready, haul away what you need, leave some to amend that spot.
-Gley
Look it up. This serves as a barrier to keep moisture and nutrients contained.
-Hugelkulture
As a nutrient and moisture trap, this method is hard to beat
-Build
Since nothing is growing in that spot, seems to be a fine place for a shed,
chicken coop, campfire pit.