I see bark and lots of goodies in that soil that require N to breakdown, I used spangum mixed in real well once and it robbed all the N out of my soil. Probably the most economical fert you could get would be some fish fert either the liquid or powder and start supplementing and see how it goes from there.

If your soil was working correctly you should not have any yellowing this early with a new seedling.

Letting the soil sit takes a few weeks or a month to blend all the organisms and nutrients.