Effect of topsoil thickness on soil organic carbon in high-yield and irrigated farmland in North China

Reduced tillage and conservation tillage probably lead to the problem of shallow topsoil and compactible topsoil in the long run. In order to solve the problem above, the experiment of different artificial topsoil thicknesses was designed. And soil organic carbon contents (0–50 cm) were determined for looking over the effect of different topsoil thickness in this experiment. There were four kinds of artificial topsoil thickness (10, 20, 30, 40 cm) in the experiment, respectively. A two-year field experiment was conducted to study the variation of soil organic carbon by using the methods of the equivalent soil mass and stratification ratio. The total results indicated that different topsoil thicknesses had a significant effect on soil organic carbon content. Compared with the initial trial in 2007, soil organic carbon content decreased by 22%–48%. Using the methods of the equivalent soil mass, it was showed that the highest soil organic carbon storage occurred in the 20 cm topsoil thickness and that the thickness too high or too low is not conducive to increase the storage of soil organic carbon. The research suggested that the stratification ratio of 20 cm topsoil thickness was higher than that of other treatments over time, and it was of good soil quality. It was concluded that different thicknesses of topsoil had different effects on organic carbon content. In the short term the topsoil thickness of 20 cm had the highest soil organic carbon content and storage. The thickness too high or too low is not conducive to increase the soil organic carbon storage. The long-term effectiveness still need to be observed.