in an ideal world there is an ideal rotation pattern. legumes following roots because the legumes leave something good in the soil (its early and i cant remember what it is - nitrogen maybe) which the roots crops will benefit from. there are other followings that benfit too such as crops that need to go into un manured space etc. sorry i am not explaining it very well, my books are not to hand, but in the real world it is sufficient on a small scale to just make sure that potatoes, aliums and brassicas are planted in different places each year to avoid build up of disease. if you want to start off on the best foot i would recommend reading joy larkcoms joy of vegetables i think she gives a good explaination. ;)
