Trifluralin (α,α,α‐trifluoro‐2, 4‐dinitro‐N, N‐dipropyl‐p‐toluidine) was applied in 1976 to Egam loam and Beason clay soils on the same field plots that were utilized in a 1973 study. The rates and methods of herbicide application, herbicide formulation and soil incorporation and plot size were also the same. Soybean (Glycine max L.) was seeded in both years with the same crop row‐width. Average herbicide residues, expressed as per cent of 0 day residues in 1976, were initially up to 7% higher in 1976 than in 1973, in both soils. The residues dissipated to about the same level, however, in both years starting 70 days after herbicide application, could be largely explained on the basis of rainfall distribution patterns in the two years. Less than 4% herbicide remained in 1976, 126 days after its application. The herbicide persistence was generally higher at higher herbicide rates in each soil, and could be described by first‐order kinetics.