There is a field like this about half a mile away from me. I assume it is a type of forage crop as it is quite patchy and there are a couple of cows now in with it. There are no visible turnips though. Couldn't see any honeybees from the gate, but there is plenty of other stuff coming into flower much closer.
Last autumn we had another yellow flowering field. Again, I thought it must be mustard/turnip type stuff for forage. Does that give a cabbagey flavoured honey? There was definitely something not very nice tasting in last autumn's honey.