Anna my Strophe -

My source is the poem as it is published in The Nation's Favourite Poems (published by the BBC and with a fwd by Griff Rhys Jones) - and that, of course, uses "practise" - because the speaker in the poem is suggesting the verb, not the noun.

No, I ain't jokin'. See the thread in info about 100 most-often misspelled ww....!