Red clover with brassicas

I don't know what an alliopathic is but assume it means something that doesn't want to be near brassicas?!? Didn't know that but suppose it's something to do with the plant families etc. Personally I grow clover under my apple trees, looks pretty and supresses the weeds.

I think it means that it chemically discourages or stops other plants growing. I want it for soil improvement and for the insects.

Doesn't seem to stop my apple trees growing

Because clover is a legume the brassicas should benefit from the fixated nitrogen. I imagine that is the thinking behind the idea.
I would wonder though if the clover whilst putting all its energy into flowering will rob the soil of other nutrients, especially Potassium and whether the brassicas can benefit from the nitrogen globules whilst the clover is still growing?
Usually a green manure crop needs to die before flowering to release its nutrients.

Interesting experiment though!

I've seen it recommended in gardening type magazines, but haven't tried it myself yet. It said that the carpet of clover helped stop cabbage root fly accessing the roots of the brassicas - but I think there was only a 30% improvement or something (can't really remember exactly, sorry), so it hardly seemed worth the risk on that basis. And presumably wouldn't help with butterflies etc... I did grow nasturtiums under brassicas once - accidentally it has to be said, they'd self seeded from the previous year . They looked amazing, but the bees found it so frustrating not being able to get at them under the anti butterfly debris netting that I lifted the netting over them at the edges - at which point the butterflies found them irresistible and laid profusely all over them, and the resulting caterpillars found an easy access route to the brassicas after all! Duh! However, I found I could easily snap them off at ground level without killing the plants when they got too exuberant and started to take over the bed, and they'd simply re-grow to provide another living green mulch. I just left all the pulled-off bits on there too to rot down. It actually worked quite well on one level...