Chlorimuron, clomazone, imazaquin, imazethapyr, and pendimethalin were each applied at five rates to soils at 10 different sites each year for three years to determine which soil properties influenced their bioactivity. Six soils in the U.S. (NC) and four in Zimbabwe were characterized for their plow-layer contents of organic matter (OM), humic matter (HM), clay mineral (CM), and silt and for pH and cation exchange capacity (CEC). At each site, the rate of each herbicide yielding 80% weed control (I80) was determined by visually evaluating the treated plots. The I80 values were then regressed with the various soil properties to determine which of them contributed to this rate. In the U.S. soils, the I80 was highly correlated with % OM (r
2 = 0.64–0.72) and % HM (r
2 = 0.55–0.69) for chlorimuron, imazaquin, and pendimethalin but was less correlated with % OM (r
2 = 0.30) and pH (r
2 = 0.31) for imazethapyr. Equations relating the herbicide rate for 100% weed control to soil properties were derived for chlorimuron, imazaquin, imazethapyr, and pendimethalin then compared with registered recommended rates for each chemical from the label. Herbicide rate equations based on similar soil parameters were taken from the literature to compare with our rate equations and with registered rate recommendations for comparison purposes and to add validity to the use of soil parameters for making herbicide rate recommendations. The rate equations, based on selected soil parameters, produced rates comparable with registered rates for chlorimuron, pendimethalin, and metribuzin and lower rates of application than registered rates for imazaquin, imazethapyr, alachlor, and metolachlor for soils with OM levels below 3.5%.