SUITABILITY OF USING 137CS AND 210PB FOR QUANTIFYING SOIL ORGANIC CARBON REDISTRIBUTION AFFECTED BY INTENSIVE TILLAGE ON SLOPING LAND

Authors: LI, YONG - CHINESE ACAD AG SCI; ZHANG, Q - CHINESE ACAD AG SCI; Reicosky, Donald; COLEMAN, D - UNIV. OF GEORGIA; BAI, L - CHINESE ACAD AG SCI; Lindstrom, Michael; LI, L - CHINESE ACAD AG SCI

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 9/22/2004
Publication Date: 9/22/2004
Citation: Li, Y., Zhang, Q.W., Reicosky, D.C., Coleman, D., Bai, L.Y., Lindstrom, M.J., Li, L. 2004. Suitability of using 137Cs and 210Pb for quantifying soil organic carbon redistribution affected by intensive tillage on sloping land. Proceedings of International Conference on Land Resource Management and Ecological Restoration in the Loess Plateau, September 20-22, 2004, Yangling, China. p. 175-184.

Interpretive Summary: Accelerated soil erosion by intensive tillage on steep slopes is a major threat for sustainable agricultural production as well as the environment in western China. Depletion of soil organic carbon and erosion are interrelated, since a decrease in organic carbon increases susceptibility of a soil to erosion. This accelerated soil erosion results in severe loss of surface soils and has a major impact on soil quality. Little is known, however, about the dynamic distribution of soil organic carbon associated with soil and tillage erosion at the field level. Radionuclides (**137 Cs and **210 Pb) have been demonstrated as an effective way to study erosion and deposition within the landscape and that radionuclides move on sloping land by the same physical mechanisms during tillage operations. This work evaluated how radionuclides could be used directly for assessing soil organic carbon redistribution as affected by intensive tillage. The profile variations of the radionuclides were measured along the slope before and after 50 plowing operations over a five-day period. The implicit assumption was that 50 tillage operations could be equivalent to 50 years of intensive tillage. The results showed that the radionuclides were significantly correlated with soil organic carbon contents at all slope locations. The results suggest that radionuclides could be used directly for quantifying dynamic soil organic carbon redistribution as affected by tillage erosion. These results are significant to 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: Spatial and temporal variation in soil organic carbon (SOC) is of great importance because of global environmental concerns. Tillage intensive erosion adversely affects SOC profile pattern. However, few direct measurements have been conducted to investigate the dynamic process of SOC as affected by intensive tillage at the field level. Our objective was to test the potential of **137 Cs and **210 Pbex for directly assessing SOC contents redistribution on the slope land as affected by tillage operation. Fifty plowing operations were conducted over a five-day period using a donkey-drawn moldboard plow on steep backslope of the Chinese Loess Plateau. Profile variations of SOC contents, **137 Cs and **210 Pb were measured at upper, mid and lower portions of the slope after 50 plowing operations. **137 Cs concentration was uniformly mixed in the upper 0-30 cm of soil whereas **210 Pbex showed a linear decrease at upper and mid portion, and exponential decrease with soil depth on the lower portion of the control slope. SOC contents of 0-30 cm layers were much higher than the soil layers below 30 cm on the control slope, and showed a similar decrease pattern to ** 210Pbex on the mid and lower portion of the control slope. Fifty plowing operations resulted in a decrease of SOC content (g/kg) by 38% and by 47% for the soil layers of 0-45 cm at upper portion and mid portion, respectively. However, SOC content in the soil layers of 0-100 cm at the lower position increased by 18% after 50 plowing operations. Weighed mean values of **137 Cs concentrations decreased from 1.48 Bq/kg to 0.29 Bq/kg at upper position, from 2.53 Bq/kg to 0.33 Bq/kg at mid position, and increased from 1.48 Bq/kg to 2.81 Bq/kg at lower position. Weighed mean values of **210 Pbex concentrations decreased from 27.71 Bq/kg to 6.15 Bq/kg at upper position, from 35.46 Bq/kg to 1.57 Bq/kg at mid position, and from 25.53 Bq/kg to 19.40 Bq/kg at lower position. Profile concentration of **137 Cs and **210 Pbex are significantly correlated with SOC contents with R**2 of 0.81 and 0.86 for the control slope, 0.91 and 0.86 for experimental slope. The results suggested that fallout of **137 Cs and **210 Pbex could be used directly for quantifying dynamic SOC redistribution as affected by tillage erosion.