A new approach for removing iron interference from soil nitrate analysis

► Fe interferes with NO3− analysis using a modified Griess-Ilosvay method. ► The Fe to NO3− ratio of Fe interference varied non-linearly with Fe concentration. ► Fe interference occurred with all buffers tested but was least with imidazole. ► We used phosphate filtration to quantitatively remove Fe from soil extracts. ► Phosphate filtered soil extracts showed no Fe interference regardless of buffer.