Hi Thierry
Personally I get at least 2 crops per year off of each bed, topping up once a year with compost, either around standing plants (normally potatoes or brassica) or prior to planting out plants grown in plugs. I do try to rotate crops on as long a rotation as possible (but don’t always get the planning right!). I never plan to leave fallow, although there are short periods when beds may be empty – at the moment I have lifted all parsnips and carrots, so those beds are now ready to take new plantings as the weather warms up.
Hope that helps?
Bluebell