Effect of Bacterial Inoculum and Fertigation Management on Nursery and Field Production of Lettuce Plants

Plant growth-promoting rhizobacteria have been applied to different vegetable crops but there is still no information on the effect of bacterial biostimulant application under variable nutritional level on lettuce seedlings and their performance after transplanting in the field. This study aimed to evaluate the efficacy of a bacterial biostimulant to enhance growth and quality of lettuce seedlings fertigated with increasing nutrient rates and to assess the efficacy of these treatments on lettuce head production. Lettuce seedlings were inoculated with 1.5 g L−1 of TNC BactorrS13 (a commercial biostimulant containing 1.3 × 108 CFU g−1 of Bacillus spp.) and fertigated with a nutrient solution containing 0, 1, 2, and 4 g L−1 of NPK fertilizer (20-20-20). At the end of transplant production, the plants were evaluated for greenhouse cultivation. The effect of fertigation rate on seedling height, dry biomass, dry matter percentage, and water use efficiency was evident up to 2 g L−1 of fertilizer in the non-inoculated seedlings, whereas fresh biomass and nitrogen use efficiency changed up to 4 g L−1 of fertilizer. The use of the bacterial biostimulant modified seedling growth and its response to nutrient availability. The inoculation of the substrate with Bacillus spp. promoted plant growth and allowed seedlings to reach the highest height and biomass accumulation. The physiological age of lettuce seedlings showed a strong influence on plant growth and production after transplanting. The bacterial treatment positively affected the yield and nitrate content of lettuce plants.