Evaluating soil organic carbon changes after 16 years of soil relocation in Chinese Mollisols by optimizing the input data of the RothC model

Abstract

Long-term intensive cultivation leads to the loss of soil organic carbon (SOC) in agricultural lands, which inevitably threatens food security and exacerbates greenhouse gas (GHG) emissions. The RothC model (Ver. 26.3win) is generally used to evaluate the changes in SOC and its responses to agricultural practices and climate change. However, previous calibrations of the RothC model emphasize the parameterization of C decomposition and neglect the effect of input data on the model accuracy. In this study, a long-term soil relocation experiment (1 m depth) in Chinese Mollisols was used to determine the effect of input parameters on the performance of the RothC model, and the optimal combination was filtered to evaluate the changes in SOC after 16 years of soil relocation. The results showed that the estimated C input from crop residues ranged from 1.22 to 2.53 t C ha−1 yr−1, and these inputs were insufficient to maintain the equilibrium state of the SOC. We also found a non-linear relationship between the initial SOC and C input, i.e., the largest C input amount was obtained under 3.24 % SOC rather than 6.31 % SOC. The difference in C input derived from estimation algorithms was the main source of model uncertainty. The simulation results indicated that from 2005 to 2020, the loss of SOC in Mollisols ranged from 2.54 to 13.90 t ha−1 when the initial SOC stocks were greater than 60 t ha−1, while the rate of SOC sequestration was 0.15 t ha−1 yr−1 when the SOC stocks was 33.03 t ha−1. Meanwhile, warming accelerated the loss and delayed the recovery of SOC in Mollisols. We suggested the equilibrium point of SOC in Mollisols under current agricultural practices was approximately 45 t ha−1. These results highlighted that Mollisols were an important C source of GHG and that a substantial capacity exists in SOC sequestration under conventional agricultural practices.