DISTRIBUTION OF N IN A SIMULATED PROFILE OF A PODSOLIC GRAY LUVISOL FOLLOWING UREA FERTILIZATION

Abstract

A laboratory leaching study, using simulated profiles, was undertaken to help explain the ability of a Podsolic Gray Luvisol to retain a considerable portion of the added urea-N in the surface 61 cm of its profile. A Podsolic Gray Luvisol, supporting lodgepole pine, in the Alberta foothills was sampled by horizons. Reconstructed profile columns were used in a laboratory leaching study to determine the effect of urea fertilization on the movement and distribution of N. Leachates were collected periodically and analyzed for total N. Upon termination of the leaching phase, soil N was fractionated by acid (0.1 M HCl) and alkali (2% NaOH) extractions. Volatilization loss of N approximated 18.5% of that retained by the fertilized columns. The addition of urea did not significantly increase the N in the leachates. Added fertilizer was retained mainly in the surface (L-F, Ah, Ae and Bf) layers of the reconstituted profiles. The largest portion of this retained N was HCl extractable. However, in the lower layers of the fertilized profiles most of the retained N was recovered in the humic fraction. It is postulated that added N as well as residual soil N mobilized by the urea treatment are retained in the soil by reaction with metal ions, hydrous oxides of Fe and Al and expanding clays. Key words: Gray Luvisols, urea, forest fertilization, N fractionation