Prilled urea 46% involves 46% of nitrogen (N) in ureic form, simply absorbed because of the leaves of plants. Absorption from the root system is slower, because urea in soil is converted (like a results of enzymatic hydrolysis) into the ammonia form available for plants, after which into nitrate form. https://tituspolyo.techionblog.com/37238918/the-basic-principles-of-cow-head-no-skin