S08 - Session P8 - Quantifying the effects of plant growth-promoting microorganisms and organic fertilizers on growth of indoor vegetable transplants

Authors: Nicklass McClintic *, Zhihao Chen, Yujin Park

The uses of plant growth-promoting microorganisms (PGPM) and organic fertilizers in crop production are considered sustainable alternatives to chemical fertilization. However, the beneficial effects of PGPM inoculation and organic fertilizer on plant growth can depend on various factors, including fertilizer types, groups of PGPM, and plant species. In this study, the effects of Azosprillium brasilense and Rhizophagus intraradices inoculation were evaluated on the seedling growth of lettuce ( Lactuca sativa 'Cherokee') and tomato ( Solanum lycopersicum 'Red Robin') under organic fertilizers derived from food waster or corn steep liquor and fermented fish by-products compared to under chemical fertilizer without PGPM. In a temperature-controlled vertical farm, the seeds of lettuce and tomato were sown in rockwool substrate, and A. brasilense (1.05 × 10 8 CFU/L) or R. intraradices (580 propagules/L) were applied through sub-irrigation weekly at and after sowing. The seedlings were fertilized with three different fertilizers at 100 ppm total nitrogen and grown at 21 °C under sole-source LED lighting at a photosynthetic photon flux density of 200 µmol∙m -2 ∙s -1 with an 18-hour photoperiod. At the transplant stage, lettuce seedlings had 75% less shoot fresh weight and 64% less dry weight under organic fertilizers than chemical fertilizer. Similarly, tomato seedlings grown with organic fertilizers had one less leaf, 36% smaller stem diameter, 40% shorter stem length, and 75% or 67% less shoot fresh or dry weight, respectively, compared to seedlings grown with chemical fertilizer. In contrast, there was little to no effects of A. brasilense or R. intraradices inoculation and organic fertilizer types on seedling growth in both species. Further research is needed to determine the effective application methods of organic fertilizers, A. brasilense , and R. intraradices to have beneficial effects of using sustainable alternatives for indoor vegetable transplant production.