"I would say that the Expert Books have been the biggest innovation in gardening publications since the death of William Robinson in 1938" - Dr Brent Elliott (Librarian, Royal Horticultural Society)
I have the later Fruit Expert one as well somewhere ...
The Expert Vegetable Notebook by Dr D. G. Hessayon should always be within arms' reach.
The 3-fold rotation: Brassicas, Others, Roots is explained.