There's a section of my back yard that has always had a strong ammonia smell. I always thought it might be coming from the weeds, or worst case scenario an issue with the septic lines :-O

I recently had the whole thing dug up to run drainage lines, which exposed the septic line. We inspected it closely and didn't see any leaks or problems. But the smell is still there!

You can see that the entire area that's been dug up is on a slope towards the garage, and is in full shade; the house blocks the sun completely, so there's a line about where the grass starts that separates full-shade from full-sun.

I've done some research, and now I believe that this smell comes from high amounts of nitrogen from bacteria in the soil.

Any suggestions on how to improve this without tilling in organic material? My main hesitation for tilling in organic material is the expense, so I'm hoping for a cheaper solution that I can do myself.