## 1 Introduction  
The total area of saline-alkali land in China is approximately 99.13 million hectares, accounting for roughly one-tenth of the country's total land area. The extensive scale, wide distribution, severe degree, and complex soil salinization and alkalinization types have become major abiotic stress factors affecting China's ecological environmental security and sustainable ecological development. These issues severely constrain ecological construction, agricultural production, and land development and utilization. Biological improvement refers to the process of ameliorating saline-alkali soil through the life activities of organisms [1, 2]. This approach is considered one of the most ecologically sustainable and economically advantageous technical measures for soil remediation. Sesbania, a herbaceous plant of the legume family, exhibits strong nitrogen fixation capabilities and is commonly utilized as a pioneer crop for saline-alkali land improvement. China has achieved a series of positive advancements in using Sesbania for saline-alkali land treatment. Sesbania planting has been widely promoted as a biological improvement technology across various regions. The \"CAS Sesbania No. 6\" Sesbania seed has been successfully trial-planted in multiple saline-alkali land regions, achieving satisfactory results. It is presently undergoing trial planting at the experimental base in Guangxi, China.  
With the increasing labor costs in agriculture, mechanical sowing has become an approach critical to enhancing the efficiency of Sesbania planting. Compared with other leguminous plants, Sesbania seeds have a smaller diameter and weigh less. The number of seeds per hole should be restricted to three to five to ensure an adequate germination rate and appropriate sowing density. However, most precision seeders for tiny seeds are tailored for single-seed precision sowing. In contrast, spoon-type seeders for multi-seed sowing are typically suited for medium-sized seeds. This inability to meet the requirements of mechanical precision sowing associated with Sesbania seeds significantly hinders the mechanization of Sesbania planting.  
The discrete-element method [3], as a numerical analysis technique specifically tailored for multi-particle systems, has been extensively utilized in the optimization analysis of seeding machinery [4; 5; 6; 7]. When conducting simulation studies on seeders using the discrete-element method, defining the characteristic parameters of the simulation model is essential. Consequently, calibrating the discrete-element model parameters of seeds becomes necessary.  
Scholars have measured discrete-element simulation parameters for seeds of significant food and economic crops such as wheat and vegetables [8; 9; 10; 11]. Regarding leguminous plants, [PERSON] et al. [12] measured the parameters of adzuki bean seeds. [PERSON] et al. [13] performed size analysis and modeling for soybeans, providing valuable references for the structural optimization of seeding devices. However, research on seed material properties and discrete-element simulation parameters relative to the \"CAS Sesbania No. 6\" Sesbania seed remains scarce, which significantly constrains the development of mechanical precision seeding for Sesbania.  
Against this background, the characteristic parameters of the Sesbania seeds were measured and the discrete-element simulation model for the \"CAS Sesbania No. 6\" seed was built. The sowing process was simulated using EDEM, which is discrete-element simulation software, and the sowing performance was evaluated through bench experiments to validate the fidelity of the model and simulation parameters. The discrete-element model of Sesbania seed in this paper has now been applied to the design optimization of precision seeders to solve the problem of mechanical sowing of Sesbania.