A single‐channel flow injection system was optimized for the determination of available iron (Fe) in soil extracts by atomic absorption spectrophotometry. This method of introducing the samples in the spectrophotometer worked particularly well in preventing blockage of the burner head which was observed in the conventional introduction of Fe for its determination by atomic absorption spectrophotometry. The appropriate selection of the manifold parameters, such as injection volume, tube length and flow rate, allowed introduction of any soil extract without requiring any pre‐treatment. This system allowed determinations at a detection limit of 0.36 mg L‐1to 5 mg L‐1, with an output of 300 determinations per hour. The results obtained for analysis of 15 soil extracts were in good agreement with those provided by the colorimetric method, with average relative deviations of 1.6%. Relative standard deviations of 4.8, 2.5, and 2.3% were obtained for contents of 1.03, 1.85, and 3.99 mg Fe L‐1, respectively.