Seed rope direct-seeding is an advanced precision sowing technique that involves encapsulating seeds within rope materials, adhering to specific spacing and quantity, and then deploying these ropes in the field as an alternative to conventional direct-seeding. This method offers the dual benefits of minimal sprout damage and precise control over row-to-seed spacing. The mechanical properties of the seed rope material and the integrity of the wrapped seeds are critical factors that influence the growth and development of the plants’ root system, which in turn is a key determinant for the optimization of the seed rope automatic seeder. This paper employed uniaxial tensile testing to investigate the mechanical properties and tensile failure characteristics of seed ropes across various materials, seed wrapping techniques, and seed soaking methods. Additionally, scanning electron microscopy was utilized to scrutinize the microstructural features of the tensile fracture surfaces of the seed ropes. The results showed that the tensile strength of paper-based seed ropes ranged from 1.80 to 2.89 N/mm, with elongation at the break between 31.4% and 47.5%, and a critical stress range of 5.67 to 9.06 N. In contrast, non-woven fabric ropes exhibited a tensile strength range of 0.91 to 1.23 N/mm², an elongation at break range of 160.3 to 284.2%, and a critical stress range of 2.86 to 3.86 N. Electron microscope scanning imagery analysis indicated that the broken fibers were disordered, and the fibers of the soaked ropes showed minor surface damage, which is attributed to the decline in tensile strength observed in soaked ropes. Regarding the phenotypic study of root growth and development, the root growth and development phenotypes of two types of rope materials across four different vegetable varieties were explored; the results indicated that the influence of the seed rope material on the root system was pronounced in the early stages of growth and development. As plants progressed to the middle stage of growth, the trend in root length mirrored that of the early stage, with the seed rope material continuing to significantly impact root system development. In the late stage of growth, the effect of the seed rope material on root growth gradually diminished as the seed rope material decomposed. Interestingly, the root length under non-woven fabric wrapping not only caught up to, but in some instances, surpassed the root length of unwrapped seeds. This research provides valuable theoretical insights and data to support the optimization of the parameters for the automatic seed rope direct-seeder.

In the design of operating procedures, structures, and control systems for agricultural machinery and equipment, it is necessary to fully consider data on the properties of relevant agricultural materials as the basis for research and design. Therefore, studying the physical properties of agricultural materials is of great significance. The basic physical parameters of agricultural materials include their shape, size, density, porosity, and moisture content. This study focuses on the triaxial dimensions, 1000-grain weight, moisture content, and tribological properties (sliding friction angle, natural repose angle) of the seeds of 16 varieties of small-seeded vegetables commonly grown in Hainan, including flowering Chinese cabbage, Chinese cabbage, lettuce, and leaf lettuce. Measurements were conducted using instruments such as a digital vernier caliper (Deli, Ningbo, China; accuracy 0.01 mm), an electronic balance (LICHEN, Shanghai, China; accuracy 0.001 g), a constant-temperature oven (Shangyi, Shanghai, China), and self-developed sliding friction angle and natural repose angle testers. Discrete element simulations were performed via EDEM 2021 software to validate the tribological properties by establishing particle models (spherical for flowering Chinese cabbage and Chinese cabbage; long–flat for lettuce and leaf lettuce) and instrument geometric models. Additionally, seed germinability (germination potential, germination rate, and germination speed) was tested using a constant-temperature incubation method. The results showed distinct differences between near-spherical and long–flat seeds in geometric characteristics, 1000-grain weight (2.27–3.06 g vs. 1.00–1.29 g), and tribological behavior (e.g., smaller natural repose angles for near-spherical seeds indicating better flowability). Plastic plates were identified as optimal for seed box guides due to lower sliding friction coefficients. EDEM 2021 simulations effectively verified the experimental data. High-germination-rate seeds (e.g., Hong Kong flowering Chinese cabbage, and Lifeng No.3 Chinese cabbage) were recommended for subsequent trials. These findings provide data support for the selection, design, and optimization of seed rope braiding machine components and sustainable seeding process.