I would not dig a fertilizer in where the plants may be shallow rooted because then you can damage the very roots that are supposed to be taking up the fertilizer. It would be OK to incorporate when digging over an empty bed. It is true that organic fertilizers need to be converted by microbes into usable form but one would hope they can do that near enough to the surface that one didn't have to disturb the roots. There's also a potential downside to working the fertilizer in too deep, because then the nutrients may end up below the "feeder" roots and wasted. I would just scratch the fertilizer gently into the surface.
