Characterizing atrazine, mesosulfuron‐methyl, and topramezone bioavailability in North Carolina soils using greenhouse bioassays

Abstract

Herbicide carryover injury to rotational crops can vary in severity depending on the influence of soil properties on herbicide bioavailability. Greenhouse bioassays were conducted with soybean, radish, and canola to evaluate differences in the bioavailability of three herbicides with carryover risk, atrazine, mesosulfuron‐methyl, and topramezone. Bioassays were conducted in three varying regional soil types with nine herbicide treatment rates including a control. Plant visual injury was evaluated weekly, and aboveground dry biomass was weighed after harvest of soybean 28 days after emergence (DAE) and radish and canola 21 DAE. A log‐logistic dose–response regression model was used to quantify herbicide‐effective concentrations for 30% (EC30), 50% (EC50), and 80% (EC80) visual injury and aboveground dry biomass reduction in each soil type. Relative herbicide‐soil bioavailability was determined through comparisons of herbicide‐effective concentrations among soil types. Pearson correlation revealed that atrazine, mesosulfuron‐methyl, and topramezone EC30 for all species were positively correlated to soil organic matter (OM) content (r = 0.56, 0.48, and 0.40, respectively) and cation exchange capacity (CEC) (r = 0.43, 0.41, and 0.45). Topramezone EC80 for soybean and radish was positively correlated to soil clay content (r = 0.51) and silt content (r = 0.51) and negatively correlated to sand content (r = −0.51) and pH (r = −0.52). Decreased atrazine, mesosulfuron‐methyl, and topramezone bioavailability in soil with high OM and CEC, decreased topramezone bioavailability in coarse‐textured soil and at high soil pH, and differential herbicide sensitivity of crop species can inform grower decisions on herbicide selections and rotational crop plans.