Lower Early Growth of Coffea arabica Seedlings Under Supplemental Irrigation Without Nutrient Replacement: A FarmBot Trial

Robotic platforms can standardize treatment delivery in early coffee experiments, but evidence on joint water–nutrient responses remains limited. We evaluated the main and interaction effects of supplemental irrigation and fertilization on Coffea arabica cv. Castillo seedlings in a 180-day outdoor FarmBot trial. Sixty-six seedlings were allocated to control (Zone A, n = 18), irrigation only (Zone B, n = 18), fertilization only (Zone C, n = 15), and irrigation plus fertilization (Zone D, n = 15). Plant height and leaf diameter were monitored together with soil moisture and temperature. Nine seedlings did not survive to the month-6 assessment, and among the remaining fifty-seven, a further three height and four leaf-diameter values were zero-coded and treated as missing because they were incompatible with living-plant dimensions; the analytical samples were n = 54 for height and n = 53 for leaf diameter. At month 6, Zone B had the lowest means (31.0 ± 5.3 cm; 30.9 ± 12.1 mm), whereas Zones C and D had the largest numerical means. One-way ANOVA detected treatment differences for height, F(3, 50) = 14.81, p < 0.001, and leaf diameter, F(3, 49) = 20.26, p < 0.001. Tukey tests showed that Zone B differed from Zones A, C, and D, while Zones A, C, and D did not differ significantly. MANOVA detected irrigation, fertilization, and interaction effects; however, the regression models explained only 36% and 43% of the variance in height and leaf diameter, respectively. Under these site-specific conditions, supplemental irrigation without nutrient replacement was associated with poorer seedling growth. The findings support evaluating irrigation together with nutrient status and drainage under site-specific conditions.