A greater understanding of the terrestrial C cycle will benefit climate change models and add to our knowledge of agriculture's potential in greenhouse gas mitigation. A field microcosm study was conducted in no-tillage and conventional tillage grain sorghum during 2004 growing season. The 5 cm diameter x 15 cm deep polyvinyl chloride (PVC) microcosms were amended with 0.5% by weight ¹³C-labelled grain sorghum residue that was grown and labelled the previous winter in the growth chamber. The empty microcosms were hammered into the soil and carefully removed as to not disturb the surrounding soil. For conventional tillage, the soil was removed from the microcosm and the residue was incorporated before returning the soil to the microcosm. For no-tillage the soil was not removed and the residue was placed on the soil surface. Non amended controls were also included for each tillage practice. The ends of the microcosms were then covered with nylon netting and returned to the soil where they were taken. One set of microcosms from each treatment was harvested at t=3, 16, 25, 40, 68, and 159 d and destructively sampled. The soil was split into 0-5 and 5-15 cm depths and analyzed for total %C and %N, ¹³C signature, ¹³C in aggregate different aggregate size classes, phospholipid fatty acids, and neutral lipid fatty acids.