I’m not an “expert”, but I do know a lot about plan physiology and seed germination. Nutrient content in the soil likely has nothing to do with how well the seeds grew. At this stage of growth. It’s all about how the soil retains water, releases water, how much aeration the soil allows for, and the solute concentration of the water/soil mixture.,(reply>), The ones with fertilizer did poorly because newly germinating seeds don’t immediately need any nutrients other that H2O, CO2, and O2. The fertilizer increases the solute concentration in the soil outside of the roots, contributing to an osmotic gradient inhibiting water uptake. In extreme cases this will ‘burn’ the roots.