The degradation of trifluralin was investigated in field soil over a 3-year period. A 2-month laboratory investigation was also performed using field soil flooded with water. Twenty-eight transformation products were isolated and identified in these studies. None of the isolated transformation products exceeded 3% of the initially applied trifluralin. After 3 years, less than 1.5% of the applied trifluralin could be detected in soil, 4% was distributed among numerous transformation products, and 38% remained as soil-bound residues, a, a, a-Trifluorotoluene-3, 4, 5-triamine, a degradation product of trifluralin, appeared to be a key compound in the formation of soil-bound residues. © 1979, American Chemical Society. All rights reserved.