Abstract: Biodiversity is one of the important measures for ecological control of weeds. In this study, a two-year (2019-2020) field experiment was conducted to explore the effects of cropping systems (sweet corn-soybean, CS; sweet corn monocropping, MC; and soybean monocropping, MS) and nitrogen application rates (0 kg·hm^-2, N0; 150 kg·hm^-2, N1; 300 kg·hm^-2, N2) on weed populations and community structure. The species number and density of weeds were counted in sweet corn seedling, booting and harvest stages during spring and autumn sweet corn cropping season. The results showed that a total of 34 weed species from 15 families were recorded in the two years. Crabgrass (Digitaria sanguinalis) was the dominant species in all treatments and accounted for 34.60%-54.95% of total weed density in different planting patterns. Barnyard grass (Echinochloa crusgalli) was the dominant species in CSN0, which accounted for 24.52% of total weed density. Melochia (Melochia corchorifolia) was the dominant species in MCN1, accounting for 13.96% of total weed density. Green bristlegrass (Setaria viridis) was the dominant species in CSN1, MCN0 and MCN2, accounting for 11.26%, 13.76% and 17.27% of total weed density in each planting pattern, respectively. Goose grass (Eleusine indica) was the dominant species in CSN2, MCN1, and MCN2, accounting for 10.72%, 10.81%, and 16.40% of total weed density, respectively. Compared to the treatment without nitrogen application, nitrogen application significantly reduced the average weed density in the CS in spring and in the MC in spring and autumn in 2019. The results of multivariate analysis of variance showed that the growth period of sweet corn had a significant impact on the average density of weeds in two years, the species number in 2020, the density-species index in 2019, and Simpson index, Shannon index and Margalef richness index of weed in 2020. Nitrogen application significantly affected the weed density-species index in 2019. Results of the detrended correspondence analysis showed that the changes of weed community composition were closely related to growing season and growth period of sweet corn, and that cropping system and nitrogen application did not have consistent effects on weed community composition. In conclusion, nitrogen application reduced weed density, while intercropping system could partially inhibit weed species richness in crop seedling stage. Sweet corn-soybean intercropping system under nitrogen application is beneficial to weed control.

Key words: weed control, sweet corn, soybean, intercropping, nitrogen application.