A 14-year trial of conventional tillage vs. no till growing corn, wheat, and cotton in South Carolina measured an increase of soil carbon in the top 5 cm from .55% to 1.4% under no-till, with no increase with the conventional till. "The crop residue additions were sufficient for increased C content of a sandy surface soil when surface tillage was absent . . . our data also show that row crop residue production was not sufficient to increase C under conventional tillage."

The most significant carbon increases in the no-till plot were in the surface layers.

Hunt, Karlen, Matheny, and Quisenberry in J. Soil and Water Cons. 51(3) 255-58