Because soil organic matter (OM) influences preemergent herbicide performance, many herbicide rates are based on soil OM content. Recent studies have found large inter‐laboratory differences in OM values whether determined by either similar or different methods. Making herbicide rate recommendations can therefore be difficult. A NaOH extraction method for determining humic matter (HM) is used by only a few laboratories but is gaining acceptance. Previous studies have shown that soil HM content also correlates with herbicidal activity. This study with several sulfonylurea herbicides found that both adsorption and herbicidal activity correlated more strongly with soil HM content than soil OM content.