The outputs of a principal component analysis (PCA) were ecologically interpreted, after the overall weed infestation indexes of all weed populations occurred in 82 sampling sites amounted to 57 5hm 2 cotton fields was assessed by visual scoring the level of weed infestation to cotton in seven scales. There was a close correlationship among the structure of weed community, crop rotation system and geographical factors. The marked difference in water content of soil resulted from the different crop rotatio...