your compost bin sounds awesome! Your allotment adventures make me think I should look into community garden type things near me... (look at me talking about literally putting down roots, woah)

Random, sorry if obvious: If you can find some, wood ash is a great additive for various micronutrients (also P and K) and managing pH.

In Mali I learned that termite mounds are also full of good things for compost (plus termites take the place of earthworms as soil aerators because worms can't survive the dry season), but that is less relevant and more "interesting fact."