The mechanisms governing the precision of seeding depth and the related agronomic outcomes are site-specific. Regional soil mechanics in the Yangtze River Basin plays a role in affecting the relationship between the seeding unit and the soil, which is a key consideration for machine design. Using four technical objectives for evaluation, a field bench experiment was conducted in the field using a market available seeding unit (2BMYFQ) to illustrate the tool-soil interactions. Two tillage treatments (i.e. no-till and rotary till), three depth settings (i.e. 2.5cm, 4.0cm and 6.0cm) and three downward forces (i.e. 0.6kN, 1.0kN and 1.2kN) were adopted in the experiment. Seeding depth, soil properties after seeding and seedling establishment rate were measured. Results showed that the interactions between the seeding unit and soil mechanics affected seeding depth significantly. The maximum seeding depth variation was 37.61%. Results showed that linear elastic force depth control assembly plus the poorly managed seedbed made it impossible for precision seeding depth control. The mechanisms leading to the poorly controlled seeding depth were identified, including both the void soil support and the over sinkage of the ground wheel. Meanwhile, the seeding unit affected soil mechanics significantly, which in due resulted into non-uniform seedling establishment rate. Results indicated that the combination of the no-till, 4cm depth setting and 1.2kN downforce provided the best precision of the seeding depth. While in the tilled soil, 4cm depth setting and 1.0kN led to the best result. Overall, the depth control performance in the tilled seedbed condition was higher than that in no-tilled soil. The research result indicated that suitable downforce selection was inherently related to both soil mechanics and agronomically defined seeding depth. Inter-relationship between the seeding unit and soil mechanics as well as on-line soil monitoring system for downforce control were key measures for precision seeding in a given agricultural zone.