Changes in soil properties under mechanical stress significantly influence the emergence and growth of crops, with different crops responding differently to these changes. To explore the impact of different soil compaction states on crop growth, field experiments were conducted in 2022 and 2023 in sandy loam soil in Manitoba, Canada. The crops (canola and soybean) were planted under three compaction levels created by a seeder’s press roller: no press roller (P0), one pass of the press roller (P1), and two passes of the press roller (P2). Soil mechanical properties and plant growth were measured for each treatment. The results indicated that soil shear strength increased significantly with each level of compaction from P0 to P1 and from P1 to P2, while soil surface resistance remained largely unaffected. Interestingly, soybean and canola responded differently to soil compaction. Soybeans showed no significant changes in emergence speed or final plant population across the three treatments. Conversely, canola exhibited over a 50% increase in emergence speed and more than a 100% increase in final plant population with either one (P1) or two passes (P2) of the press roller, compared to the no press roller (P0) treatment. These findings provide valuable guidance for agricultural producers and engineers in adjusting the down pressure of seeder press wheels when planting different crops.

Achieving high sowing precision for small and irregularly shaped seeds remains a significant challenge in air-suction plug-tray seeding systems due to frequent seed slipping and detachment during the seed-picking and conveying processes. To address this issue, a novel seed cap incorporating a seed-carrying plate structure was developed. A DEM-CFD gas–solid coupling model of the seed-metering device was established for metering chili pepper seeds. With suction (negative) pressure, seed-carrying plate height, and suction-hole diameter as affecting factors, simulations with a quadratic orthogonal rotational combination were conducted. Response surface methodology (RSM) was employed for multi-objective parameter optimization, followed by comparative bench test verification. The results indicate that the interaction between suction pressure and suction-hole diameter had a highly significant effect on the multiple-filling rate. The optimal combination of working parameters was determined as a suction pressure of 25.5 kPa, a seed-carrying plate height of 0.2 mm, and a suction-hole diameter of 0.4 mm. Experiments with the seed-metering machine demonstrated that under these optimal parameters, the single-seed qualification rate reached 95.09%, the miss-seeding rate was 3.06%, and the re-seeding rate was 1.85%. Compared to the conventional seed cap without a seed-carrying plate, the single-seed qualification rate increased by 4.49%, while the miss-seeding and re-seeding rates decreased by 2.06% and 2.43%, respectively. The seed-carrying plate structure effectively reduced the dependence of the seed-metering device on high suction pressure, providing a technical reference for the research and development of precision plug-tray seeding of irregular seeds.