Changes in Natural ¹⁵n Abundance Associated With Pedogenic Processes in Soil. Ii. Changes on Different Slope Positions

Rather marked variations in δ a 15 N values were obtained in a study carried out on samples taken from four soils belonging to the Weyburn soil association. The δ a 15 N 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 approximately 5 m. This characteristic enrichment in the heavier isotope of total nitrogen of surface horizons may represent long-term immobilization of partially oxidized ammonium N into the organic N fraction; δ a 15 N 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.