The increasing demand for sustainable agricultural practices has driven the adoption of organic farming and increased demand for organic transplants. However, transplant growth is often lower in organic fertilizers compared to conventional fertilizers. This is most likely caused by low nutrient availability in organic fertilizers. On the other hand, increasing organic application rates has the potential to induce salinity stress/toxicity. We hypothesize that biostimulants can complement organic fertilizers in crop production by enhancing nutrient uptake and increasing crop tolerance to abiotic stress and thus close the yield gap between organic and conventional fertilizers. In this study, we tested three biostimulants: humic acid and molasses (MicroLife Soil and Plant Energy) and two microbial based biostimulants with different beneficial microorganism populations (MicroGrow CM and MicroGrow Supreme). Four organic fertilizers were tested with biostimulants, two of which were animal-based fertilizers: Sustane (4-6-4, turkey manure) and Drammatic (2-4-1, derived from fish scrap) and two of which were plant-based fertilizers: Nature Safe (7-7-7, corn steep liquor) and Pre-Empt (fermented sugarcane molasses). After applying to peat-based substrate, we analyzed the leachate nutrient availability weekly. Both fertilizer and biostimulant affected available nutrient concentrations in substrate. Additionally, transplant performance was evaluated to determine the effect of biostimulant and organic fertilizer combination on transplant growth, mineral nutrition, and physiological responses. Transplant growth varied across the different combinations of biostimulants and organic fertilizers tested, suggesting potential interactions between these factors. Some biostimulant treatments, particularly in combination with specific organic fertilizers, showed a trend towards improved early growth compared to the organic fertilizers alone. These results showed synergistical effects between biostimulants and organic fertilizers, indicating the positive role of biostimulants in organic transplant production.
