I must admit that crop rotation defeats me although I do rotate in a way.
I know why you should rotate crops, I know which crops rotate where, I just don't know how.   
 
  
Let me explain, to start with brassicas should be followed by roots ... correct ?
OK, I grow PSB and sprouts in the brassica bed ... PSB and sprout greens keep going till May most years, but I need to sow parsnips and carrots long before that and just to compound things, I grow overwintering onion set and seed .. not to mention garlic.
How do you fit that lot into the scheme of things ?
Next plot, roots should be followed by peas & beans.
Again that is almost impossible as the parsnips are still going strong in February and March, but I need to dig it over in October to sow my overwintering peas and broad beans (and I don't like parsnips stored in sand or a clamp)
About the only section that kind of works is brassicas following peas & beans, but even here there is some clashing as the runner beans keep going till at least October, maincrop peas till September, but early sprouts need to be planted out by June at the latest and Purple Sprouting soon after.
And to cap it all, these beds are supposed to be dug in the autumn and left over winter.
And, and, and... what about if you save your own seed, which means things like parsnips, carrots, leeks etc need to be left for at least another 6 months.
I can see that if you have multiple beds you could plan it quite easy, but most people only have a small plot (like me) where it's virtually impossible to do.
So I think I will continue the way I have for the last 50 odd years and just make sure nothing grows in the same spot every year. I will still plant my early Brussel Sprouts between my early Potato rows, and my over-wintering crops in the most sheltered part of the garden. The potatoes get a good dosing of blood fish & bone meal which the sprouts will also enjoy and I can lime the sprouts after the potatoes have been dug and as long as I don't manure my root crops I think everything will be OK.
All in all I think that crop rotation should be at the back of every gardeners mind but certainly not be ruled by it.
Sorry 'bout that.  
