Posted: 29/09/2015 at 06:49
Think we're looking at two different things - if using a rotational plan the section where onions are to be grown will already have been manured for the legumes and limed for the brassicas in previous rotations - that should be sufficient for the onions - adding manure to that section will not suit the root crops which would be grown with the onions when working to a rotational plan.
That's how a basic crop rotation for a vegetable garden works - the planting conditions are an accumulation of what has gone before.
If starting from scratch and not using a rotational plan, then add manure.
The advice does not conflict - just different ways of providing the same conditions.