I was planning on just knowing all 4 biome essays really well, and no soil at all.. bad idea?
Just know your biomes atleast one question has to come up if not two, characteristics hasn't come up in a while so I'm banking on that!
For Geoecology, soils and biomes tend to come up in a 2:1 ratio. Either 2 Biome Qs and 1 Soils, or 2 Soils and 1 Biome.
So really, if you don't mind chancing your arm, just learn either Biomes or Soils inside out, everything you possibly can.
The main risk in doing that is your chosen subject will definitely come up but it could be the sh*tiest question ever!