I feel Nitrogen is a riddle that I would like to understand. One thing that I have recently learned is that certain amino Acids help the plant in taking in Ca. Many Organic growers in Oregon and Washington use pelleted chicken manure and feathers as a source of N. I have not used them as I am still using a small amount of urea. One thing that I have learned using Sap Analysis is that I am using less and less each year as my soil improves.