Plant uptake of selenium and L Se ‐values in different soils

Abstract Rye‐grass was grown in six different soils with four additions of 75 Se‐labelled selenite through six cutting in a pot experiment. Following the last cutting, the soils were extracted with a series of solvents to fractionate the residual soil selenium. The plant content of added and total selenium was determined. The results showed that equilibrium between added and native selenium was obtained before the third cutting, giving a nearly constant L Se ‐value for the last four cuttings. The L Se ‐values differed between the soils, and there was a positive correlation between the L Se ‐values and the plant uptake of native selenium. In accordance with this, the best correlation with the total selenium concentration in the plants was obtained with the isotopically exchangeable selenium in the soil after the last cutting. It is concluded that isotopically exchangeable selenium approximates the fraction of soil selenium from which plant uptake of selenium occurs.