I did a little experiment with my garden spots last couple of years. I got the soil ammended last year and the production doubled atleast. Almost no disease in my tomatoes. Everything overall just looked much better. Ive never really done a before!/after before that but it made a huge difference in my garden. That being said, there is a thousand reasons for crop failure. Theres alot of reading you can do on fertilizer utilization when your ph is off. Some crops will absolutely not grow if the ph isnt right.