Changes in Topsoil Organic Carbon of Croplands in Heilongjiang Province of China, 1981-2011.

Changes in Topsoil Organic Carbon of Croplands in Heilongjiang Province of China, 1981-2011

Abstract:

Maintenance of soil organic carbon (SOC) is critical not only to soil fertility, but also to environmental sustainability in agroecosystems. Thus, the sequestration of carbon into soils has been of increasing concern, and serves as one of the strategies to offset anthropogenic CO2. Heilongjiang Province has the largest area of croplands in China, and thus the croplands have a large potential of carbon sequestration. The overall goal of this study was to estimate the changes in organic carbon density and storage of topsoil (0-20 cm) in cultivated soils from 1981 to 2011 in Heilongjiang of NE China on the basis of measured data and those acquired during the second national soil survey in China, and further explored the main factors influencing carbon sequestration in croplands during the past 30 years.

The average carbon density in the topsoil in Lindian, Hailun, and Baoqing counties in 2011 were estimated to be 38.28，62.96, and 3.95 Mg C ha-1, respectively. In comparison with the values in the early 1980s, the results revealed a carbon gain of 5.77 Mg C ha-1 for cultivated soils in Baoqing County, with a sequestration rate of 0.19 Mg C ha-1 yr-1. In contrast, a remarkable loss of carbon was observed in Lindian (6.62 Mg C ha-1) and Hailun (14.84 Mg C ha-1), and the SOC sequestration rates were -0.22 and -0.49 Mg C ha-1 yr-1, respectively. The estimated topsoil SOC pools in Lindian, Hailun, and Baoqing counties in 2011 were 6.18, 18.59, and 30.53 Tg C, respectively. Over the past 30 years, the changes in SOC pools were -1.02, -4.39, and 2.15 Tg C for the three counties, respectively, which were -14.1, -19.1, and 7.6% of the SOC pools in the 1980s.

The analyses showed that soils with higher initial SOC density had larger carbon loss rates, indicating that the soil type was the main natural factor influencing the changes in SOC density. The increase of C pool in paddy soils was predominantly contributed to carbon sequestration in cultivated soils. Additionally, returning of crop straw in the state farm had a profound effect on the improvement of SOC density. Considering carbon sequestration, our results suggest that future agricultural management should focus on the conversion of dryland soils to paddy soils and straw returning into soils in Heilongjiang Province, NE China.