CHANGES IN NATURAL 15N ABUNDANCE ASSOCIATED WITH PEDOGENIC PROCESSES IN SOIL. II. CHANGES ON DIFFERENT SLOPE POSITIONS

Abstract

Rather marked variations in .delta.a15N values were obtained in a study carried out on samples taken from 4 soils belonging to the Weyburn soil association. The .delta.a15N of the total N of well-drained depressional profiles dropped sharply with depth and, in contrast, for upper slope positions was relatively constant to a depth of .apprx. 5 m. This characteristic enrichment in the heavier isotope of total N of surface horizons may represent long-term immobilization of partially oxidized ammonium N into the organic N fraction; .delta.a15N of the total N more closely represents past soil-forming processes, while that of the nitrate N appears to reflect, in addition, recent N cycle stresses.