Challenges and strategies in estimating soil organic carbon for multi-cropping systems: a review

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Multi-cropping systems play a crucial role in global agricultural production. Accurately estimating the soil carbon sequestration capacity of multi-cropping systems is of significant importance for enhancing agricultural productivity, mitigating greenhouse gas emissions, and reducing carbon footprint. However, soil carbon cycling is more complex in multi-cropping systems compared with single-cropping systems, and existing assessment methods cannot accurately estimate soil carbon sequestration in multi-cropping systems with high operability. Here, we reviewed the accuracy and efficiency of the three primary global soil carbon assessment methods, including statistical models, process-based models, and the Intergovernmental Panel on Climate Change (IPCC) steady-state method. Our study concludes that it is difficult to simulate the dynamic evolution of soil organic carbon (SOC) using the statistical models, while the well simulation through process-based models demands a large amount of data. Additionally, the IPCC Tier 2 method cannot be directly applied to estimate SOC in multi-cropping systems due to mismatches in parameters and time steps. We suggest modifying the structures and parameters of the IPCC Tier 2 method by revising the inventory unit and redetermining the parameter values, which should efficiently address its bottleneck in estimating SOC for multi-cropping systems. Moreover, long-term experimental observations and multi-model ensemble simulations are beneficial for determining the parameter values to address the data deficiencies in IPCC Tier 2. This study aims to explore pathways for improving the accuracy of SOC estimation in multi-cropping systems and, thus, carbon footprint calculation worldwide.