Rice (Oryza sativa L.) root coatings were investigated to determine the amounts and mineralogical properties of the coatings during plant growth and in different soils under field conditions. X‐ray diffraction, electron microscopy, high gradient magnetic separation, and chemical methods were employed. Determinations of oxygen transport by different rice cultivars were made in vitro.Rice cultivars, growth stage, and soil type were significantly related to the amount of iron oxyhydroxide (FeOOH) on field‐grown rice roots. Accumulation of FeOOH was < 2% of dry root weight 7 days after flooding of the soil, increased to a maximum of about 10% at plant maturity and decreased slightly thereafter. Of the four soils studied, two Vertisols had less FeOOH accumulation on root surfaces than two Alfisols. Of the four cultivars characterized (‘Brazos’, ‘Labelle’, ‘Lebonnet’, and ‘Bluebelle’), Brazos had the largest amount of O2 released from the roots and precipitated the largest amount of FeOOH on the roots when field grown in three of four soils. Lake Charles clay was the only soil in which Brazos rice did not rank highest in percent FeOOH on roots and in grain yield.Goethite (α‐FeOOH) and lepidocrocite (τ‐FeOOH) were identified in rice root coatings that were ultrasonically dispersed and concentrated by high gradient magnetic separation.