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

Abstract

The fate of soil organic carbon (SOC) transported and redistributed by erosion over steep agricultural landscapes is uncertain. The effect of topography, slope, and slope position on SOC redistribution must be considered. Our objectives were to (1) determine the spatial patterns of both tillage and water erosion‐induced SOC redistribution, (2) evaluate the compensating effects of tillage‐induced soil redistribution on SOC loss due to water erosion, and (3) quantify changes of SOC storage between 1898–1954 and 1954–1998 periods. To meet these objectives, we conducted field sampling and investigated a cultivated hillslope in the Fangzhuang gully of Xigoumao catchment in Chinese Loess Plateau. Soil organic carbon redistribution 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. The major losses of SOC over the entire hillslope are attributed to severe water erosion. Significant increase of SOC at the lower field boundaries on the summit and upper backslope resulted from tillage‐induced soil redistribution by moldboard plowing. Tillage‐induced soil redistribution increased SOC and compensated for 8–14% of the SOC losses due to water erosion during 1898–1998, but the total soil erosion reduced SOC pool over the steep cultivated hillslope of the Loess Plateau. During the period 1898–1954, the net SOC loss from the entire hillslope was 1.65 t C ha−1 (0.03 t C ha−1 yr−1). Within the period 1954–1998, the net SOC loss was 10.65 t C ha−1 (0.24 t C ha−1 yr−1). The positive relationship between SOC with 137Cs and 210Pbex confirmed the utility of fallout radionuclides as a promising method for tracing tillage and water erosion impacts on SOC dynamics covering a timescale of 45 to 100 years.