Parameter Optimization of a Double-Screw Trenching-Fertilizing Machine Based on the Discrete Element Method

To address the issues of narrow row spacing, complex terrain, and low fertilization efficiency in trenching and fertilizing operations for mountainous tea gardens, a dual-spiral integrated trenching and fertilizing machine was designed, and its key parameters were optimized using the discrete element method (DEM). The research aimed to improve the stability of trenching depth, uniformity of trench width, and fertilization accuracy to meet the needs of precision agriculture in tea gardens. A soil–tool interaction model was established using Extended Discrete Element Method (EDEM) simulation software, and the forward speed, spiral blade rotation speed, and spiral angle were optimized via the Box–Behnken design of response surface methodology. Simulation results showed that the optimal parameter combination was a forward speed of 0.37 m·s−1, spiral blade rotation speed of 202.31 r·min−1, and spiral angle of 23.13°, achieving a trenching depth stability coefficient of 98.12%, width uniformity coefficient of 97.44%, and soil coverage rate of 75.32%. After optimizing the fertilization device parameters, the coefficient of variation for fertilization uniformity decreased to 5.80%, the bilateral symmetry index approached 0, the target layer trenching rate reached 89.86%, and the fertilizer drift loss rate was only 3.00%. Prototype tests in tea gardens verified that the machine achieved a trenching depth stability coefficient of over 94.28% and fertilization uniformity of 94.29%, meeting the design requirements. This study provides an efficient trenching and fertilizing solution for hilly and mountainous tea gardens, promoting the transformation of trenching and fertilizing machinery from experience-driven to model-driven design.