Hey welcome to the game.

Wish you enjoy it and have good luck playing.
Here some info about how we use dirt, as said up here it is used to improve trees quality and not to improve your lands quality.
We also use lands with nice quality soil to improve the quality of our crops, but this mainly happens when the world starts, because once the quality of the crop is higher than the soil it will not help us improve.
http://ringofbrodgar.com/wiki/Treeplanters_pothttp://ringofbrodgar.com/wiki/Finding_h ... ,_and_soilTo answer the best dirt quality question, idk which has been the best discovered so far, I can say I have seen Q 104 in world 6 though.
Imho, nodes with around Q 60 are fairly common, and players that happen to own a node with Q 85/90 or superior can make nice profits selling soil.