Soil Properties and Phosphorus Isotopic Exchangeability in Cropped Temperate Soils

Isotopically exchangeable phosphate (P) is the main source of P for most crops. The amount of P that is located on the solid phase of a soil and that can exchange with P in the soil solution can be calculated knowing the concentration of water-extractable P (CP ) and two kinetic parameters: (i) the ratio between the total introduced radioactivity added as 33P in a soil/water system and the radioactivity remaining after 1 min in this solution (R/r1minute ) and (ii) the rate of disappearance of 33P from the solution with time (n). The aim of this article was to propose statistical models describing R/r1minute and n as a function of CP and other soil properties. By doing so we made the hypothesis that it is possible, knowing CP and selected soil properties, to calculate the amount of P located on the solid phase of the soil that remains isotopically exchangeable after 1 min and 60 min (Pr1minute , Pr60minutes ). This work was done in two steps. First, isotopic exchange kinetic experiments were carried on nin...