Submitted to: Pedosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2006
Publication Date: 6/1/2007
Citation: Zheng, J., He, X., Walling, D., Zhang, X., Flanagan, D.C., Qi, Y. 2007. Assessing Soil Erosion Rates on Manually-tilled Hillslopes in the Sichuan Hilly Basin Using 137Cs and 210Pbex Radionuclides. Pedosphere. 17(3):273-283. Interpretive Summary: Soil erosion can be caused by wind, by water and/or by the effects of tillage mechanically moving soil particles down a hill. It can be difficult to determine how much soil has been detached and moved by different processes, as well as conserved by various practices, and the exact locations where soil loss has occurred. This study measured the quantities of two different radioactive isotopes (Cesium-137 and Lead-210) down a slope profile, to determine where soil erosion had been greatest (lower amounts of the isotopes present, below a reference value) to where soil erosion was low or sediment deposition had occurred (higher amounts of the isotopes present, above a reference value). Local farmers in China till this field by hand hoeing, always from the bottom of the hill to the top. They also redistribute sediment deposited in adjacent drainage ditches back up onto the field as a conservation practice, effectively reducing the amount of net soil loss. Hoeing tillage and slope convexity caused the greatest estimated soil loss near the top of this hill. Erosion rates decreased down the hill, and significant sediment deposition was found at the very bottom of the profile where the slope was very flat. This research impacts scientists, conservationists, farmers and others interested in determining where soil detachment and sediment deposition have occurred in agricultural landscapes, and how cropping, tillage and conservation practices can impact the soil loss.
Technical Abstract: Purple soils are widely distributed in the Sichuan Hilly Basin and are highly susceptible to erosion, especially on the cultivated slopeland. But quantitative assessment of the erosion rate is difficult due to the manually-tilled small patches of lands, sophistic structure of land use, and steep hillslopes. Here, 137Cs and 210Pbex measurements were used to investigate the spatial pattern of soil erosion rates and then assess the effect of hoeing tillage in a purple slope-land in Shangqiao Village, Neijiang City, in the Sichuan Hilly Basin. The 137Cs and 210Pbex inventories at the top of the cultivated slope were extremely low, though these values were highest at the bottom of the cultivated slope. By combining the erosion rates provided by the 137Cs and 210Pbex measurements, the weighted mean net soil loss was estimated to be 3100 t km-2 yr-1, which is significantly less than the 6930 t km-2 yr-1 for a 10° cultivated slope obtained from the runoff plots at the Suining Station of Soil Erosion. The spatial pattern of soil erosion rates on the steep agricultural land shows that manual tillage plays an important role on soil redistribution along the slope. Also, the traditional farming system of “Tiaoshamiantu” has a significant effect in reducing soil loss, leading to the comparable lower net erosion rate on the field.