Pedologists often lay out soil from each horizon like this for great profile overviews, even though the horizons are thicker
We use Hori Hori knives or other fixed blades to poke around the pit. I was partial to the wood handled Mora knives early on in my career. They were about $10 - much cheaper than they are now. I found a good substitute in the later part of my career which had a blunted point. That held up pretty well.