Abstract: 【Objective】The Inner Mongolia Autonomous Region is one of the areas with the most abundant soybean ecological types in China. Understanding the diversity and distribution of the soybean varieties according to their maturity groups (MGs) in the region is not only of great importance for rational distribution and exchange of the germplasm, but also providing a model for soybean varietal maturity group classification and planting regionalization of the country. 【Method】To classify soybean varieties from the region into different maturity groups, 21 standard varieties which represent MG000, MG00, MG0, MGⅠ, MGⅡ and MGⅢ of soybean were introduced from North America as references in this study. In the field tests, 120 local varieties collected from the major soybean producing areas were planted in Zhalantun, Chifeng, Hohhot, Hangjin Rear Banner and Ejin Banner together with the MG reference varieties. Fifteen plants with the similar growing tendency were observed, and the dates of VE (emergence), R1 (beginning bloom), R7 (beginning maturity) and R8 (full maturity) were recorded. The method of "Classifying MG by Individual Years" was used for maturity group classification of the varieties. Geographical distribution and the north boundary of the representative varieties in the Inner Mongolia Autonomous Region were surveyed. 【Result】Varieties from the Inner Mongolia Autonomous Region were classified into 7 MGs of MG0000, MG000, MG00, MG0, MGⅠ, MGⅡ and MGⅢ. Three varieties matured earlier than MG000 were classified into MG0000, and 6, 20, 43, 35, 8, and 5 varieties were respectively classified into MG000, MG00, MG0, MGⅠ, MGⅡ and MGⅢ. The MG0000 varieties were mainly distributed in the northeast foothill area of Daxinganling Mountains and northeast section of Hulunbuir Plateau. The MG000 varieties were distributed in the east foothill area of Daxinganling Mountains. The MG000 varieties were distributed in west section of Hulunbuir plateau and the south and north alpine areas of Yinshan Mountains. The MG00 varieties were distributed in cool area of Yinshan Mountains and east and south section of Daxinganling Mountains. The MG0 varieties were distributed in Hulunbuir and Xingan League traditional agricultural regions in the Nen River valley at the eastern Daxinganling Mountains, Tongliao city, the mountainous area of north Chifeng and the warm areas of the Yinshan Mountains outer hill. The MGⅠvarieties were distributed in the cool-warm area of southeast section of Daxinganling Mountains, Chifeng hilly mountains and south foothill area of the Yinshan Mountains. The MG Ⅱ varieties were distributed in mild area of the south section of Daxinganling Mountains, Tumochuan Plain at south foothill area of Yinshan Mountains and Liangwai region of the Hetao Plain. The MG Ⅲ varieties were distributed in West Liaohe Plain warm area, Daqing Mountain gully slope area，Hetao Plain irrigated area and Alxa Plateau oasis area. According to the MGs and planting area of the test varieties and referring to the agricultural regionalization and meteorological data, soybean planting regionalization of the Inner Mongolia Autonomous Region was proposed, and soybean MG geographical distribution map in the Inner Mongolia Autonomous Region was drafted. In addition, the variety introducing scheme in the Inner Mongolia Autonomous Region and eco-regional adjustment plan for the uniform tests were proposed. 【Conclusion】Soybean varieties in Inner Mongolia were distributed widely in geological regions and diverse in MGs and ecological types. The MG classification could optimize the distribution, strengthen the exchange of soybean germplasm within and out of the region, highlight the targets of soybean breeding and extension, and accelerate the broad utilization of the varieties.

Key words: soybean, Inner Mongolia Autonomous Region, maturity group, planting regionalization