It is not recommended to use potting mix with fertilizer incorporated into the next. I know people use it but again not recommended. Use a well draining commercial potting mix (Fafard 52 ot ProMix) for the air layer and best to start in a smaller pot, a 2 or 3 gal, till rooted out. You can apply a light drench of 20-20-20 liquid fertilizer. Once rooted out, you can up-pot to a 7gal till rooted and then plant out.