LAUSR

BACKGROUND The efficacy of an herbicide as soil treatment agent may be largely affected by soil characteristics. Understanding the relationship between herbicide efficacy and soil characteristics can provide decision basis for herbicide application according to local conditions. This study was aimed to explore the effect of soil characteristics on herbicidal activity of atrazine as a model herbicide to barnyard grass and thus to find an indicator for the herbicidal activity assessment of an herbicide against weeds. RESULTS The herbicidal activity of atrazine to barnyard grass varied greatly among the tested soils with the medium inhibition concentration (IC50 ), based on the amended concentration, ranging from 1.07 to 10.91 mg/kg. Uptake of atrazine by barnyard grass was negatively correlated with its adsorption onto soils, whereas it was positively related to the concentration of the herbicide in in situ pore water (CIPW ). Comparable IC50 values ranging from 1.14 to 1.38 were obtained from CIPW in the tested soils with much smaller variation coefficient compared to those based on the traditional concentration (Csoil ) of this herbicide in soils determined by extraction with organic solvents. CONCLUSION The concentration of atrazine in in situ pore water could be reliable to evaluate its bioavailability and herbicidal activity to barnyard grass. CIPW of an herbicide in soil could be an indicator for guiding the practical application rate. This article is protected by copyright. All rights reserved.