Differences in soil organic carbon dynamics in paddy fields and drylands in northeast China using the CENTURY model

Abstract

Soil tillage and land-use conversion have been widely discussed as primary factors for soil carbon sequestration and neutralising CO2 discharge. In this study, the CENTURY model was applied to simulate long-term soil organic carbon (SOC) dynamics and quantify the response to tillage management at the farm scale in northeast China. This freeze–thawing agricultural area was originally covered with wetlands and grasslands but is now dominated by paddy fields and drylands. The regional spatial background of SOC was determined with 1.5-km grid sampling, and the difference in land use was identified. The CENTURY model was developed and validated with historical SOC monitoring data. The values of the correlation coefficient and the root mean square error between the simulated and measured SOC were 0.771 and 2.24%, respectively. The long-term historical SOC dynamics since 1949 were simulated under land-use conversions. The slow SOC decreased from 18.18gCkg−1 in 1949 to 7.29gCkg−1 in 2011. The passive SOC continually decreased by 6.11% from 1949 to 2011, while the active SOC displayed a large variation over the same temporal scale. The SOC responses under two sets of scenarios of straw return rate and tillage management were compared. The paddy fields displayed better SOC recovery than the drylands did. The SOC concentration responses to four straw return rates of 25% (present status), 40%, 60%, and 80% were simulated in paddy fields and drylands. Maintaining the 80% straw return rate recovered SOC stocks to 55.30% in drylands and 50.90% in paddy fields. The adoption of no-tillage scenarios caused the SOC stocks to increase by 0.04gkg−1y−1 in drylands and 0.14gkg−1y−1 in paddy fields. The long-term simulations indicated that agricultural development decomposed the SOC pools and that the drylands suffered more significant impacts. The simulations suggested that the paddy fields had a 7–20% faster SOC recovery speed than did the drylands and were especially sensitive to tillage management scenarios. Analysis of the series SOC responding data with the CENTURY model determined that the SOC status can recover in 30 years with continual 30-year 80% straw return and conservation tillage. The long-term SOC trends simulation also provided the SOC response range (−8.1–102.34%) under specific tillage management and straw return conditions, which shows that the model can predict future dynamics in the freeze–thawing agricultural area.