urea is a synthetic organic....which is a chemical. yes it has carbon so you are telling the truth when you tell your customers that you are using organic fert. I think many lawn care companies do what you do. if i were to sell a synthetic organic to my customers i would use nitroform 38-0-0 as it is in my opinion a better product with better long term results than 46-0-0.
(it feeds the soil too.)