Optimization of pro-tray configuration, substrate composition, and seedling age for chili and brinjal plug seedlings intended for robotic transplanting

Labor scarcity has accelerated interest in robotic transplanting, whose reliability depends on seedling geometry and root plug cohesion. This study optimized pro-tray configuration, substrate composition, and seedling age for chili and brinjal plug seedlings. A greenhouse experiment (three replications) evaluated three tray configurations (98 cells, 19 cm3; 72 cells, 38 cm3; 126 cells, 22 cm3), two substrates (coir pith alone and a mixed substrate of coir pith, vermiculite, and perlite, 3:1:1 by volume), and five seedling ages (25–45 days after sowing) at 5-day intervals. All three factors significantly affected most traits. For chili, the 126-cell tray with mixed substrate at 35 days after sowing produced a height of 166.3 mm, stem diameter of 2.16 mm, root-ball integrity of 98.0%, and tray canopy density of 72.66% (desirability, 0.62); the 98-cell tray with mixed substrate at 30 days had equal desirability. For brinjal, the 98-cell tray with mixed substrate at 30 days after sowing produced a height of 149.33 mm, stem diameter of 2.51 mm, root-ball integrity of 96.66%, and tray canopy density of 87.33% (desirability, 0.65). Biometrically suitable transplanting ages were 30–35 days for chili and 30 days for brinjal. These solutions provide end-effector design inputs requiring machine-performance validation.