A technique is described for the correction of abnormally high iron concentrations measured by X‐ray fluorescence spectrometry in alfalfa tops contaminated with soil. By adding to alfalfa samples, known amounts of different soils representative of the textural types occurring in the sampling area, the concentration of iron and aluminium in the contaminating soil was determined by subtracting the concentrations of the elements in the uncontaminated controls. A single regression equation relating concentrations of iron in the contaminating soil as a function of soil aluminium was suitable for correcting iron concentrations measured in all plants contaminated with soils of a loamy texture. Another regression equation was derived to correct values of iron in plants contaminated with sandy soils.