Efficacy of atrazine [2-chloro-4-(ethylamino-6-(isopropylamino)-s-triazine] applied preemergence to no-tillage and conventional-tillage corn (Zea mays L.) was studied in the field for 2 yr at two locations. Other variables examined were lime treatments, atrazine rates, and acid-forming (NH4NO3) vs. nonacid-forming (NaNO3) nitrogen fertilizers. Mean surface soil pH levels during the growing season were higher with no-tillage than conventional tillage, because of the retention of lime in the surface in no-tillage vs. mixing it with the soil in conventional tillage, but there was no consistent increase in atrazine efficacy or longevity in one system over the other. Liming significantly increased atrazine efficacy and longevity in both no-tillage and conventional-tillage systems. Increased rates of atrazine increased weed control and longevity of the herbicide. Use of NaNO3 as a nitrogen source resulted in increased atrazine efficacy and longevity as compared with use of NH4NO3 during the first year, which was relatively dry, but had no effect during the second year, which was relatively wet.