Vegetable transplant production is a critical phase that enhances the efficiency, sustainability, and profitability of vegetable cropping systems. In the U.S. Midwest, many organic vegetable growers produce their own transplants due to the limited commercial availability of certified organic transplants. A major constraint in this process is managing nutrient availability, which can compromise transplant quality. While a variety of organic amendments exist, there is limited empirical data on their comparative effectiveness and application strategies in transplant production. This two-year greenhouse study evaluated the effects of selected organic amendments on the growth, root system architecture, and nutritional composition of pepper (Capsicum annuum) transplants grown in 25-cell trays. The experiment was arranged in a randomized complete block design with four replications. Treatments included three dry organic fertilizers bone meal (3-15-0), blood meal (12-0-0), and feather meal (12-0-0) mixed at recommended label rates with growing media at the time of seeding. Additionally, treatments included a liquid fish emulsion (5-1-1 AquaPower™), compost amendment, conventional synthetic (15-5-15 Peters Excel®), and a no-fertilizer control. Data was collected on plant height, stem diameter, plant biomass, tissue nutrient content, and chlorophyll content of leaves. Root and shoot biomass were also collected followed by analysis of root architecture using WinRhizoTM software. Synthetic fertilizer treatment resulted in the highest plant biomass and height, followed closely by blood meal, with no statistically significant difference between the two in either year. Root surface area and volume were greatest in plants treated with feather meal, followed by those receiving blood meal. Weekly EC and pH data collected on the growth medium leachate samples showed that there was a strong negative correlation between them that is when EC was high, pH was low across the treatments, with compost treatment having the highest EC and pH overall. These findings underscore the influence of organic fertilizer source on pepper transplant growth and nutrient status, contributing to improved organic transplant production practices and enhanced transplant quality for vegetable growers.
