The amount of C released (respiration) on a given date of sampling provides an indicator of how active the microbial community is and in part reflects the availability of substrates at the date of sampling. The respiration in Blount1 and Bennington2 soils increased with incubation at all glyphosate application rates. Whereas, in Blount0 soil the respiration after a small initial increase, decreased to nearly zero as the incubation proceeded in the presence of glyphosate. This differential response would suggest that Blount1 and Bennington2 soils that received glyphosate repeatedly under field conditions had a shift in microbial community that was adapted to degrading glyphosate (Haney et al., 2002, Araújo et al., 2003 and Lancaster et al., 2010), hence demonstrated an increase in respiration with increasing glyphosate application rate. These results also suggest there is a glyphosate dosage history microbial response as the Bennington2 soil with a much higher number field applications per year had highest respiration values. Whereas, Blount1 soil with lower annual glyphosate applications had lower respiration compared to Bennington2 soil. Araújo et al. (2003) also demonstrated strongest response in microbial activity in soil with several years of glyphosate exposure.