Soil carbon storage and mineralization rates are influenced more by the amount of carbon added to the soil than by physical disturbance like tillage. A long-term study found that different tillage methods did not significantly affect overall soil carbon levels, but did change how carbon was distributed in the soil layers. The highest rates of carbon breakdown were in the top soil layer, while the lowest rates were deeper down. The amount of carbon added to the soil and the type of organic matter present were more important factors in determining carbon breakdown rates than the intensity of tillage. A model that considered the relationship between carbon input and breakdown rates accurately predicted how soil carbon levels changed over time in different soil layers.