Degradation of Bromoxynil in Regina Heavy Clay*

Summary A spectrophotometric method was developed to detect bromoxynil in Regina heavy clay, and the breakdown under different temperature and moisture conditions was studied. At rates equivalent to 14 kg/ha, over 50% of the applied bromoxynil was degraded in 2 weeks at 25°C and at moisture levels in excess of the wilting point. Losses at 18°C were slightly slower. Little breakdown occurred in sterile soil, indicating that microbial degradation could be an important factor contributing to bromoxynil breakdown under field conditions. Paper and thin‐layer chromatographic techniques were used to isolate and identify soil degradation products. In addition to the parent compound small amounts of 3,5‐dibromo‐4‐hydroxybenzamide and 3,5‐dibromo‐4‐hydroxybenzoic acid were detected.