CONVECTIVE TRANSPORT OF ORTHOPHOSPHATE (P-31 AND P-32) IN SEVERAL MANITOBA SOILS

Abstract

The convective transport of ³¹P and ³²P in three soils was investigated using elution and miscible displacement techniques. The rate of movement of both ³¹P and ³²P compared with that of water was greatly retarded by soil-phosphorus interactions; the retardation of movement increased with increasing rates of phosphate fixation of the soils. The rate of ³¹P and ³²P movement in soil was influenced by the mode of phosphate application. The rate measured by pulse input was greater than that measured by continuous input. The rate of ³¹P movement was invariably greater than that of ³²P. Also, the specific activity of the effluent obtained from soil columns was different from the specific activity of the phosphate solution added, particularly at the start of elution. The change in specific activity and the slower rate of ³²P movement than that of ³¹P was attributed to exchange of ³²P with soil phosphate. It is suggested that isotopes such as ³²P, which can exchange with their unlabeled form in the medium, cannot be used to determine accurately the movement of ions in media such as soils.