Urea is nitrogen fertilizer which is essentially taking the place of ammonium nitrate. I only use it on bare soil before I plant and rake it in and water it down so I can't tell you how to use it on growing plants. However, your farm extension office will be able to help you if application rates are not on the bag. You have to be careful with it because it will kill plants if applied to heavily, kinda like the spots in your lawn where your dogs urinate, there is urea in urine.