Question
i also am doing a project on whether commercial fertilizer will make a plant grow bigger than cow manure would. which one do you think would make a plant grow bigger

Answer
It depends on your Soil.  Cow Manure, in modest doses, would definitely yield the best results if you have a healthy sample of Soil.  Commercial Fertilizer tends to induce deficiencies.  But remember:  No plant will ever grow bigger than its DNA pre-determines.  People tend to forget that.

Good luck on your project, Charlie.