Powdered organic fertilizer is crucial for sustainable agriculture, but its poor flowability and hygroscopic compaction and caking nature cause frequent blockages during mechanized strip application. While a single Johnson–Kendall–Roberts (JKR) discrete element method (DEM) model simulates powder flow well, it fails to reflect the mechanical breakage of hard caked lumps. Thus, this study established a comprehensive DEM model simultaneously simulating both powder and caked lumps. Based on coarse-graining theory, 0.147 mm particles were scaled to 2 mm spheres. Contact parameters (e.g., JKR surface energy) were calibrated using response surface methodology, yielding a repose angle simulation error of only 0.18%. The actual three-dimensional (3D) geometry of caked lumps was reconstructed via 3D scanning, and breakage mechanical parameters were accurately calibrated by combining uniaxial compression tests with a Bonding model (errors for ultimate load and displacement < 2%). Applying this model to an anti-blocking fertilizer discharge device, simulations and performance tests demonstrated an acceptable macroscopic representation of both powder flow and lump breakage. The optimized device achieved a strip application uniformity coefficient of variation of 3.87–6.40%. By simulating the complex coexistence of powder flow and lump breakage, this study provides a feasible parameter calibration method and numerical reference for optimizing anti-blocking discharge devices.