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Title: Changes in soil organic carbon induced by tillage and water erosion on a steep cultivated hillslope in the Chinese Loess Plateau from 1898-1954 and 1954-1998

Author
item LI, YONG - CHINESE ACAD AG SCI
item ZHANG, Q - CHINESE ACAD AG SCI
item Reicosky, Donald
item Lindstrom, Michael
item BAI, L - CHINESE ACAD AG SCI
item LI, L - CHINESE ACAD AG SCI

Submitted to: Journal of Geophysical Research-Biogeosciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/27/2006
Publication Date: 3/1/2007
Citation: Li, Y., Zhang, Q.W., Reicosky, D.C., Lindstrom, M.J., Bai, L.Y., Li, L. 2007. Changes in soil organic carbon induced by tillage and water erosion on a steep cultivated hillslope in the Chinese Loess Plateau from 1898-1954 and 1954-1998. Journal of Geophysical Research-Biogeosciences. 112:G01021.

Interpretive Summary: The fate of soil organic carbon (SOC) transported and redistributed by erosion over the steep agricultural landscapes is uncertain. The effect of topography, slope and slope position on SOC redistribution must be considered. Depletion of SOC and erosion are interrelated, since a decrease in organic carbon increases susceptibility of soil to erosion. This work evaluated how radionuclides could be used directly for assessing SOC redistribution as affected by intensive tillage to determine the spatial patterns of both tillage and water erosion-induced SOC redistribution and evaluate the compensating effects of tillage-induced soil redistribution on SOC loss due to water erosion. To meet the objectives, a field sampling was conducted on a cultivated hillslope of Fangzhuang catchment in the hilly-gully regions of the Chinese Loess Plateau. Significant increase of SOC amounts at the lower field boundary on concave slopes of the summit and sharp decrease on convex slopes of the backslope resulted from tillage-induced soil redistribution by moldboard plowing; whereas, the overall losses of SOC over the entire hillslope are attributed to severe water erosion. Tillage-induced soil redistribution could increase SOC and compensated for 8%-14% of the SOC losses due to water erosion during 1898-1998, but on the whole soil erosion reduced SOC pool over the steep cultivated hillslope of the Loess Plateau. Soil erosion reduced the SOC pool over the steep cultivated hillslope of the Loess Plateau. The results suggest that radionuclides could be used directly for quantifying dynamic SOC redistribution as affected by tillage erosion. These results are significant to Chinese farmers and policy makers in that intensive tillage results in substantial soil redistribution and losses of soil carbon. This information will assist scientists and engineers in developing improved tillage methods to minimize carbon loss and to improve soil carbon management. Farmers can develop and utilize new management techniques for enhancing soil carbon by changing tillage intensity to minimize changing soil properties across a sloping landscape.

Technical Abstract: The fate of soil organic carbon (SOC) transported and redistributed by erosion over the steep agricultural landscapes is uncertain. The effect of topography, slope and slope position on SOC redistribution must be considered. Our objectives were to (i) determine the spatial patterns of both tillage and water erosion-induced SOC redistribution, (ii) evaluate the compensating effects of tillage-induced soil redistribution on SOC loss due to water erosion, and (iii) quantify changes of SOC between 1898-1954 and 1954-1998. To meet these objectives, we conducted field sampling on a cultivated hillslope of Fangzhuang catchment in the hilly-gully regions of Chinese Loess Plateau. Soil organic carbon was calculated by multiplying SOC concentration by total soil redistribution (TSR) including both tillage and water-induced soil redistribution derived from 137Cs and 210Pbex inventories and from the tillage erosion prediction (TEP) model. Our results showed that the hillslope soil had an 89% decrease of 137Cs inventories for the last 45 years and a 55% decrease of 210Pbex inventories for the last 100 years. Significant increase of SOC amounts at the lower field boundary on concave slopes of the summit and sharp decrease on convex slopes of the backslope resulted from tillage-induced soil redistribution by moldboard plowing; whereas, the overall losses of SOC over the entire hillslope are attributed to severe water erosion. Tillage-induced soil redistribution could increase SOC and compensated for 8%-14% of the SOC losses due to water erosion during 1898-1998, but on the whole soil erosion reduced SOC pool over the steep cultivated hillslope of the Loess Plateau. During the period 1898-1954, net SOC loss from the entire study hillslope was 1.65 t C ha-1 at the rate of 30.01 kg C ha-1 yr-1. Within the period 1954-1998, the net SOC loss was 10.65 t C ha-1 at the rate of 236.72 kg C ha-1 yr-1. The positive relationship between SOC and both 137Cs and 210Pbex confirmed that fallout radionuclides are a promising method for tracing tillage and water erosion impacts on SOC dynamics covering a timescale of 45 to 100 years.