1 23 Plant and Soil An International Journal on Plant-Soil Relationships ISSN 0032-079X Volume 365 Combined 1-2 Plant Soil (2013) 365:283-290 DOI 10.1007/s11104-012-1380-7 Absorption of 15 NH 3 volatilized from urea by Citrus trees Rodrigo M. Boaretto, Dirceu Mattos, José A. Quaggio, Heitor Cantarella & Paulo C. O. Trivelin