Rb was applied to the topsoil in order to trace the potassium which was taken up from the topsoil by plants. The resulting K/Rb ratio in plants increased when plants came into contact with the Rb free subsoil. This change in the K/Rb ratio enables the calculation of the K uptake from the subsoil. the average of the K uptake from the subsoil by spring wheat was 35% of the total uptake.
Key words K-uptake - K/Rb ratio - Subsoil