In modern agricultural mechanization, granular materials such as fertilizers and crop residues (e.g., straw) are widely involved in operations like fertilizing, seeding, harvesting, and mulching. The mechanical behavior of these particles—such as movement, stress response, breakage, and deposition—directly affects application uniformity, operation efficiency, and mechanical wear. The Discrete Element Method (DEM), as a core tool for analyzing multiparticle systems, has become increasingly valuable in the structural optimization and performance prediction of agricultural machinery. This chapter focuses on two representative granular subjects—fertilizer granules and individual crop straw stems—and systematically investigates their physical and mechanical properties, contact parameter calibration, and DEM modeling strategies. The content includes the construction of a comprehensive granular property database, simulation-based analysis of fertilizer discharge dynamics, and a mechanical model of straw stems incorporating failure characteristics. These studies provide both theoretical foundations and numerical references for intelligent control and equipment design in precision agriculture.