I have used low biuret urea to greatly increase spring flowering, it works great. According to the Citrus Production Manual, published by the University of California either Low Biuret Urea (46-0-0) or Potassium Phosphite (0-28-26) can be used. The spray to increase bloom should be sprayed between December 15 and to February 15. For warm greenhouse production the earlier spray of December 15 provides a much better bloom. I can find no where in the University's production manual that it states that nitrogen inhibits flowering.