The first day after glyphosate addition, all treatments for C mineralization were significantly different than the control except the 53 rate. The influence of the surfactant may be partially responsible for the lag of the 53 rate, possibly from surfactant lysis of microbial cells or from a surfactant– glyphosate interaction. This result was repeated in a separate experiment with product-grade glyphosate and analyticalgrade glyphosate, where it was apparent that the surfactant suppressed the 53 rate initially in the product-grade compared with the 53 analytical-grade material that contained no surfactant (data not shown).