The L values of four paddy soils and one United Kingdom soil were determined under water-logged and aerobic conditions over a period of 7 weeks using rice and ryegrass as the respective test crops. Under water-logged conditions, the L values attained a constant level in the course of the growing period, indicating that isotopic equilibrium between the added P32 and the soil was achieved. Under aerobic conditions, the equilibrium L values tended to be lower than those determined under water-logged conditions. This was taken as an indication of an increase of labile soil phosphorus by reduction of ferric iron. © 1969 Martinus Nijhoff.
