Prediction of soil organic carbon in an intensively managed reclamation zone of eastern China: A comparison of multiple linear regressions and the random forest model.

Organic carbon is a key component of soils and plays a fundamental role in soil fertility and climate change. Determining the importance of potential drivers of soil organic carbon (SOC) and thus predicting the distribution of SOC are important for measuring carbon sequestration or emissions. Coastal wetlands are precious land resources that are currently undergoing rapid reclamation in China. The alternations in soil physicochemical conditions caused by reclamation can strongly impact the cycle of organic carbon. However, identification of the important drivers of SOC dynamics and prediction of SOC using the potential drivers remain largely unclear. In this study, we used classification and regression tree (CART) to identify the importance of the potential drivers of SOC at 241 sites from an intensively managed reclamation zone of eastern China. Multiple linear regressions (MLR) and random forest (RF) models were applied to predict the distribution of SOC using continuous variables, such as the contents of Cl, CaO, Fe2 O3 , Al2 O3 , SiO2 , clay, silt, and sand as well as the soil pH, along with categorical variables, such as land use and reclamation duration. The results indicate that the soil/sediment pH was the most important variable impacting SOC, followed by the Cl and silt contents. The RF and MLR involving all predictor variables produced much higher R2 and lower error indices than the RF and MLR models involving independent variables (pH and CaO). RF performed much better than MLR as it revealed much lower error indices (ME, MSE, and RMSE) and a higher R2 than MLR. The superiority of RF in predicting SOC is related to its capability to deal with non-linear and hierarchical relationships between SOC and predictors. Analyses of land use effects on SOC dynamics indicated that paddy soils were superior in sequestering SOC than other land use types, which is likely ascribed to the rapid desalination and dealkalization of paddy field management. Therefore, paddy field management is recommended as an environment-friendly approach for managing newly reclaimed lands.