Soil test kits are really meant to test soil from your garden rather then made up compost. I doubt if you will ever get a true reading
from a mixed compost. The fact that all the feed is added means that it is bound to be in patches, not throughout as it is in garen soil that has been unaltered for months.
I tend to agree! soil test 'kits' are not meant for this type of thing.
Was this a seed compost, or a multi - purpose, or a specific onion compost that you were growing your hoped-for champions in??
don't all the Onion experts make their own blends? ;)
But if there was any Potash or Potassium in it in the form of powdered fertilizer it should have shown up in the test, as it is water soluble in compost as it is in soil.
If,as stated above that fertilizer will only appear "In Patches" then presumably if you potted 100 tomatoes up then you should expect some to be planted in infertile compost ?
I don't think so myself,the fertilizer should be adequately mixed so as to be evenly distributed throughout a bag.
I must have just got a duff bag.
Far from considering myself an Onion Expert,I do know that a lot of the real experts use M3 compost and don't blend their own compost like you suggest.
Wink Wink. ;) ;) ;) ;)