Irregular germination of carrots.

My guess is slugs.  Same thing here.  They seem to work their way down a row, until presumably they are full.  When I looked closely I could see the missing ones had been chewed off at soil level.  Re-sowed, with a liberal sprinkling of the blue pellets of death (under enviromesh so birds can't get them).   Lo and behold lots of carrots sprouting up and lots of dead slugs.

I seem to have this problem, I'll apply nematodes I think.