Introduction: Soybean (Glycine max L.), with 20% oil and 40% protein, is economically one of the most important plants of the legume family and has the largest cultivated area among the plants of this family. Weeds are the most important factor in reducing crop yield and the main limiting factor in optimal soybean production. Improper use of herbicides may also lead to problems such as herbicide residues groundwater contamination, and weed resistance. Therefore, it is important to adopt appropriate management solutions that do not include the above problems. One of the non-chemical solutions for weed management is the use of cover crops. Cover crops are effective in suppressing weed biomass. Considering the serious problems caused by the competition of weeds with soybean in Golestan province and the significant decrease in soybean yield, this research was conducted with the aim of investigating the effectiveness of cowpea, mung bean and millet cover crops in the management of weeds of three soybean cultivars in Golestan province.

Materials and Methods: A factorial experiment was conducted as a randomized complete blocks design in three replications in Gorgan and Aliabad Katoul, Golestan province in the crop year of 2018-2019. The test factors were soybean cultivars in three levels, Saman, Katoul and Sari as the first factor and six levels of weed management including pure soybean cultivation with herbicide use, pure soybean cultivation with weeding operations, simultaneous cultivation of mung bean cover crops (Vigna radiata L.) together with soybean, cowpea cover crops (Vigna unguiculata L.) together with soybean and of millet cover crop (Panicum miliaceum L.) together with soybean and pure soybean cultivation without any management operations (control) infested with weeds, was considered as the second factor. Height, density and dry weight of weeds were measured three times, 5, 10 and 15 weeks during the growing season.

The data obtained were subjected to analysis of variance (ANOVA) using SAS software version 9.1 (SAS Institute, Cary, NC, USA). The significant differences among the treatments were determined by the least significant difference (LSD) test (p< 0.05). Figures were drawn by Excel 2019.

Results and Discussion: The results showed that the highest percentage of reduction in dry weight, leaf area, height, number of species and density of weeds compared to the control was related to the treatments of cover crops, and the lowest percentage of dry weight, leaf area, height, number of species and density of weeds was 71.67, 64.27, 57.71, 44.71 and 70.91% belonged to herbicide treatment respectively. The highest soybean grain yields were observed in the amount of 26.36%, respectively, compared to the control treatment in Saman cultivar in Aliabad under the conditions of weeding. The highest uniformity index with 0.69 was obtained from Gorgan, which showed 32.69% more uniformity than Aliabad. Also, the highest Peleo species richness index with 0.95% was obtained from Aliabad, which was 9.27% more than Gorgan. The highest Sorensen similarity index with 0.6867 and 0.4622% was obtained from herbicide and weeding treatments, and the lowest amount of this index was observed in the treatment of mung bean, cowpea and millet cover crops with 0.0556%. The highest uniformity index of Saman with mung bean cover crop treatment and Sari with millet cover crop treatment was 0.98% and 0.973%, respectively, and the lowest uniformity index of Ketol with herbicide management treatment was 0.841%. The highest index of menhinic richness was obtained from the treatment of Saman in cowpea cover crop, and Katoul in mung bean cover crop (1.064%), and the lowest index was obtained Saman in weeding management (0.791%), which is statistically similar to the treatments Mung bean cover crop in Saman and Katoul cultivars, and the treatments cowpea cover crop in Katoul and Sari cultivars were in the same group.

Conclusion: The most favorable treatment for Weed Control Efficiency and the highest percentage of reduction in dry weight, leaf area, and height, number of species and density of weeds was simultaneous cultivation of cover crops and the lowest amount of all these traits was obtained in the herbicide treatment.