The use of herbicide glyphosate has increased significantly in recent years due to the widespread use of Roundup Ready crop varieties and increased adoption of conservation tillage systems.  In this study, we evaluated glyphosate mineralization as affected by tillage system, cotton variety, and row spacing.  The field experiment was established in 2004 on a Compass sandy loam using a factorial arrangement with four replications.  The tillage treatments were conventional and non-inversion deep tillage (conservation) systems.  Roundup Ready and conventional cotton varieties were planted at standard (40") and 15" row spacings.  Soil samples were collected at 0-10 cm depth in spring of 2005.  Laboratory soil incubation was carried out using ¹⁴C-glyphosate for 91 days.  Preliminary data showed that 32 to 46% of the initial radioactivity was converted to ¹⁴CO₂.  Glyphosate mineralization was significant higher in conservation tillage soils than in conventional till soils regardless of other treatments.  Soil microbial community as indicated by PLFA profiles will be assessed.