Determining the optimal dose of Trichoderma harzianum for the morphophysiological development of Pinus radiata seedlings in the nursery

Pinus radiata seedling production needs alternatives that enhance vigour and reduce chemical inputs. This study quantified the effect of Trichoderma harzianum dose on morphophysiological performance. We ran a randomised complete block design with 48 experimental units, four blocks, four treatments, and three replicates per treatment within each block, with weekly assessments for 20 weeks. We applied 0.75, 1.00, and 1.25 g L−1 to the substrate as a drench, 100 mL per seedling every 15 days, and included an untreated control. Intermediate doses increased height. The 1.00 g L−1 treatment reached 19.2 cm and 0.75 g L−1 reached 18.9 cm, increases of 3.7 cm and 3.5 cm over the control, equivalent to 24% and 22%. The overall effect lay at the significance threshold and Tukey separated the control in group a from 0.75 and 1.00 g L−1 in group b, while 1.25 g L−1 fell in ab. Stem diameter did not differ, p = 0.230. Fresh weight did not reach significance, p = 0.139, and biomass did not differ, p = 0.2610. We recommend 1.00 g L−1 due to greater height and a more uniform response, and we propose post-transplant validation using survival and dry weight.