Abstract:Parsing of main stem phenotype is of great significance for understanding plant growth patterns, optimizing planting density and improving crop yield. In this study, one soybean main stem node detection model YOLO?SN based on improved YOLO v8n was proposed for multiple breeding scenarios, and the phenotypic parameters of main stem node number, internode length and main stem length were analyzed. Firstly, aiming at the problems of poor model adaptability and high missed detection rate caused by significant differences in the characteristics of soybean main stem nodes in three typical breeding scenarios, including open field, indoor and artificial climate chamber, respectively. The DAF (Deformable attention fusion module) module is constructed in the backbone to enhance the model?s ability to pay attention to node regions in multiple scenarios;Secondly, for the problem that the small pixel share of main stem nodes leads to recognition difficulties, the DDH (Dynamic decouple?head) was designed in the head to improve the model?s ability to perceive the main stem nodes of soybeans;Finally, the dynamic non?monotonic focusing mechanism WIoU (Wise intersection over union, WIoU) was designed for further improving the convergence speed and generalization of original network YOLO v8n. The experimental results show that the main stem node detection accuracy, recall, average precision mean and F1?score are significantly improved in a single scene, and the comprehensive performance in multiple scenes reaches 90.6%, 85.1%, 90.0% and 87.8%, respectively, which are all better than the mainstream target detection models. The absolute error and coefficient of determination of the number of main stem nodes, the distance between nodes and the length of main stem were 0.42, 12.6 pixels, 17.4 pixels and 0.88, 0.80, 0.82, respectively. This study provide an effective method for the accurate parsing of soybean plant phenotypes in typical breeding environments, as well as offering technical support for intelligent breeding of soybeans and other legumes.