IMMOBILIZATION OF (NH4-N-15 IN 3 SOILS BY CHEMICAL AND BIOLOGICAL PROCESSES())

An investigation was made of the effect of chemical and biological pro cesses on ammonium immobilisation. Three soils, autoclaved and unautoc laved, were used. Labelled ((NH4)-N-15)(2)SO4, was added to soils that were then incubated at 25 degrees C for 0, 1, 5, 10 or 20 days. At th e end of incubation, clay-fixed (NH4+)-N-15, organic N-15 and KCl-extr actable mineral N-15 was determined. In autoclaved soil, fixation by c lay accounted for up to 31% of applied (NH4+)-N-15 over a 20 day incub ation. In unautoclaved soils (NH4+)-N-15-N fixed by clay decreased whe n nitrification reduced the quantity of KCl-extractable (NH4+)-N-15-N. Incorporation of (NH4+)-N-15 into organic matter in unautoclaved soil accounted for 6-13% of applied N, whereas in autoclaved soil, only 2- 7% was recovered in the organic N pool. The data show that both chemic al and biological processes play important roles in immobilisation of (NH4+)-N-15 in soils. Copyright (C) 1996 Elsevier Science Ltd