Traditional manual tillage significantly affects soil redistribution and CO2 emission in agricultural plots on the Loess Plateau

Traditional manual tillage using hand tools is widely used by local farmers in hilly and mountainous regions in China and many South-east Asian countries. Manual tillage could result in severe soil erosion, redistributing slopes from upslope areas (erosion) to lower slopes (deposition). This soil redistribution process may potentially affect the soil carbon cycle, but few studies have quantified soil CO2 emission under different manual tillage practices. In the present study we evaluated the soil redistribution and its effects on in situ CO2 emission as affected by manual tillage of different intensities on three short slopes representing typical cultivated landscapes on the Loess Plateau. Soils were removed at 2, 6 and 10 cm depths by three types of hand tools, namely a hoe, mattock and spade respectively, from the upslope and subsequently accumulated at the downslope to simulate soil erosion and deposition processes by traditional manual tillage. Across the tilled hillslopes, soil CO2 emission was reduced at sites of erosion but enhanced at sites of deposition. Tillage with greater intensity (i.e. hoeing < mattocking < spading) resulted in greater change in CO2 emission. This change in soil CO2 emission was largely associated with the depletion of soil organic carbon (SOC) stocks at erosion sites and the increments of SOC available for decomposition at deposition sites. Moreover, with increasing tillage intensity, soil redistribution by manual tillage shifted the hillslope from a C sink to C neutral or even a C source. Furthermore, manual tillage resulted in substantial changes in soil CO2 emission and redistributed soil in amounts that dwarf animal-powered tillage. The results of the present study imply that manual tillage-induced soil redistribution could have a large effect on the C balance across the local landscape and therefore may have considerable implications for estimates of regional and global C budgets.