ABSTRACT VERMICOMPOST APPLICATION AS A FERTILIZER SOURCE AND SUBSTRATE AMMENDMENT FOR SEEDLINGS AND TRANSPLANTS: PRACTICAL APPLICATION AND MICROBIAL ACTIVITY ANALYSIS Stephanie A Brace, PhD Cornell University 2016 Fertility management of seedlings/transplants can be difficult especially when they are grown in an organic production system. Transplants are grown in small containers with substrates that usually contain a low nutrient holding capacity. Organically supplied nutrients are primarily slow release and depend on biological processes to convert organically bound nutrients into a plant available form. Temperature influences both microbial activity and plant growth. Little information is currently available on the effect of vermicompost additions on microbial activity and subsequent plant performance in soilless substrates. Commercially produced vermicompost (VC) is a worm processed form of compost that can be used to provide fertility in organic systems. The source and method for producing VC are extremely variable. Therefore, the objective of this work was to test performance of seedlings/transplants in response to fertilizers, temperature, and sources of vermicompost. In addition, the microbial activity in vermicompost will be determined. Germination and transplant experiments were conducted using various quantities, sources and application methods of VC. Seeds of pepper ‘Calwonder’ (Capsicum annuum L.), tomato ‘Rutgers 39’ (Solanum lycopersicum L.), petunia ‘Celebrity White F1’ (Petunia x hybrid) and snapdragon ‘Rocket Mix F1’ (Antirrhinum majus L.) were included. Topdressing VC instead of incorporating led to higher fresh weight (FW) of tomato, pepper, petunia, and snapdragon. The source of VC had significant effect on plant growth of tomato and peppers in seedling and transplant stages. Vermicompost extract (VCE) applied at 5 applications per week was adequate to produce marketable seedlings of the four species above. A trial was conducted to compare the performance of several different granular organic fertilizers on 10 cm containers of ‘Celebrity’ tomato transplant growth at average daily temperatures of 10, 15, or 20 °C. The results indicate that the fertilizers perform well at 15 and 20 °C, but plant growth and nutrient availability was reduced at 10 °C. Results indicate that at 15 and 20°C Sustane, Verdanta, and Microstart can be substituted for conventional synthetic fertilizers for quality plant growth and decreased leaching. In another trial, VC, autoclaved VC and Sustane were applied in six combinations to determine if the microbial community in VC facilitated nitrogen mineralization. Plant growth and microbial parameters were measured at 2 week intervals for 6 weeks. By week 6, the FW of trts with VC or autoclaved vermicompost (AVC) applied performed better than the control. Very little difference in plant growth was found between VC or AVC treatments. Microbial activity measurements found that most of the activity of the microbes was concentrated in week 0 and 2. Respiration decreased in week 4 and then increased in week 6. The microbial activity was greatest in the first 2 weeks and coincided with the highest levels of N in the substrate and leachate.