Four applications is an absolute minimum to substain. To keep the natural bio activity going, you want to maintain constant levels of N too. I am not going to pretend to know soil microbiology but I do know their activity goes up and down with available Carbon and Nitrogen. Active soil microbes will improve the soils more than any thing we can do short term. I do apply PHC product, it does have innoculates, sugars humates and seaweed. It also has a good trace mineral and Iron boost. Most of our track home sites start off with a lots of trash, heavy conpaction and a layer of sand over clay. Aeration is a very good idea.