Physical–Mechanical Properties of Tomato Seedlings for the Design and Optimization of Automatic Transplanters

This study was based on the hypothesis that the hybrid type and its physical–mechanical properties significantly influence the operational efficiency of transplanting systems. Understanding these properties is essential for optimizing the performance of semi-automatic and automatic transplanters. To test this hypothesis, a completely randomized design was implemented to evaluate the physical–mechanical properties of tomato seedlings. A total of 1350 seedlings from three F1 hybrids—Natalie (H1), CID (H2), and Gavilán (H3)—cultivated in central Mexico, were analyzed. The statistical analyses included mean comparisons using Tukey’s test and multiple linear regression to estimate the center of mass (CM). The results indicate that H2 was notable for its total height (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mrow><mi mathvariant="normal">h</mi></mrow><mrow><mi mathvariant="normal">t</mi></mrow></msub></mrow></semantics></math></inline-formula> = 311.76 mm), canopy development in X, Y, and Z axes (170.24 mm, 106.84 mm, and 98.14 mm, respectively), stem diameter (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mrow><mi mathvariant="normal">d</mi></mrow><mrow><mi mathvariant="normal">s</mi></mrow></msub></mrow></semantics></math></inline-formula> = 3.65 mm), total weight (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mrow><mi mathvariant="normal">w</mi></mrow><mrow><mi mathvariant="normal">t</mi></mrow></msub></mrow></semantics></math></inline-formula> = 11.92 g), <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mrow><mi mathvariant="normal">d</mi></mrow><mrow><mi mathvariant="normal">e</mi></mrow></msub></mrow></semantics></math></inline-formula> (78.36 mm) and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mrow><mi mathvariant="normal">d</mi></mrow><mrow><mi mathvariant="normal">p</mi></mrow></msub></mrow></semantics></math></inline-formula> (233.40 mm) distances, and oscillation period (T = 0.88 s). H1 had the highest stem height (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mrow><mi mathvariant="normal">h</mi></mrow><mrow><mi mathvariant="normal">s</mi></mrow></msub></mrow></semantics></math></inline-formula> = 53.18 mm), <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mrow><mi mathvariant="normal">w</mi></mrow><mrow><mi mathvariant="normal">t</mi></mrow></msub></mrow></semantics></math></inline-formula> = 11.76 g, and root ball (RB) moisture content (MC) (77.36%). H3 had the largest <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mrow><mi mathvariant="normal">d</mi></mrow><mrow><mi mathvariant="normal">s</mi></mrow></msub></mrow></semantics></math></inline-formula> = 3.70 mm, as well as the highest MC in the stem (94.51%) and the remaining foliage (92.92%). Regarding mechanical properties, the average adhesion force (AF) was 4.606 N (H1), 7.470 N (H2), and 3.815 N (H3). The average root ball punching force (RBPF) was 0.36, 0.48, and 0.25 N, respectively. The lowest static friction coefficient (SFC) on a galvanized steel sheet was 0.936. The drop test (DT) revealed an average residual substrate mass of 0.148 g at a height of 500 mm. It can be concluded that the interaction between hybrid type, transplanting age, and MC plays a critical role in the efficient design of semi-automatic and automatic transplanting equipment. This interaction enables process optimization, ensures operational quality, reduces seedling damage, and ultimately enhances and increases the long-term profitability and sustainability of the equipment.