Prilled urea 46% includes 46% of nitrogen (N) in ureic form, very easily absorbed from the leaves of plants. Absorption from the root system is slower, because urea in soil is converted (as a results of enzymatic hydrolysis) into the ammonia form available for plants, and then into nitrate form. https://caidenfijll.tinyblogging.com/an-unbiased-view-of-fertilizer-urea-composition-80846133