THE INFLUENCE OF CROPPING SYSTEMS ON WEED COMMUNITIES IN THE COTTON FIELDS OF JIANGSU PROVINCE
种植制度对江苏省棉田杂草群落影响的研究

The overall weed infestation indexes and density of all weed populations occurr ing in both the rice_cotton crop rotation and continuous dry_cropping sys tems of the main cotton belts in Jiangsu Province were surveyed over five years continuously. The succession patterns of weed communities and weed occurrence we re studied through statistical analysis in space and time. The results showed th at there was a close relationship between the structure of weed community and th e level of weed infestation and cropping systems. Under the rice_cotton crop rot ation system, the density of hydrophilous weeds such as Echinochloa crusgalli, Alternanthera philoxeroides and Malachium aquaticum was the highest, whi le that of xerophilous weeds (e.g., Digitaria sanguinalis) was lowest. Ho wever, there was marked linear relationship between abundance and time, with abu ndance of hydrophilous weeds (e.g., E. crusgalli) decreasing, and that of x erophilous weeds as (e.g., D. sanguinalis) increasing with time, when cott on was gro wn continuously in the fields with the rice_cotton rotation system. After four years continuous cotton growing, the structure of weed community seemed to tend to stable condition. In the cotton fields with cotton cropping system, there wer e dense density of xerophilous weeds as dominants and no marked change of weed c ommunity structure between different years. Moreover, the marked difference of w eed community structure and weed density occurred between two different cropping systems. The influence of cropping systems on weed community was much more sign ificant than that of geographical factors.