Determining the Most Sensitive Indicators of Soil Carbon Transformation to the Land-Use Change from Intact Rangeland to Cropland, Western Iran

This work aimed to assess the sensitivity of soil organic carbon (SOC) quality and quantity indicators to land-use change (LUC) using carbon management index (CMI) and soil quality index (SQI) constructed by a principal component analysis (PCA). We tested this approach by analyzing soil after 40 years of LUC from intact rangeland (IR) to cropland (CL). The analyzed soil physico-chemical properties were: soil total organic C (STOC), particulate organic C (POC), hot-water extractable carbohydrate (HWC), total glomalin (TG), easily extractable glomalin (EEG), and difficulty extractable glomalin (DEG), soil organic C stock (SOCS), total nitrogen, bulk density (Bd), sand, silt, and clay fractions, pH and electrical conductivity (EC) values, equivalent calcium carbonate (ECC) content, cation exchange capacity (CEC), and the TG/STOC ratio values. Measured biochemical endpoints were soil basal respiration (BR), substrate-induced respiration (SIR), microbial biomass C (MBC), metabolic quotient (qCO(2)), and beta-glucosidase and cellulase activities. Results showed significantly lower values of all studied soil properties for the CL than the IR soil, except for the pH value, clay content, ECC, and CEC, which were significantly higher in the CL than the IR soil. Values of CMI (126.8%) and SQI (73.3%) indices were significantly lower in IR than CL soil. The contribution of the minimum data set (MDS) to the SQI analysis selected TG/STOC ratio and BR as the main indicators of SOC change. The parameters can be applied for the monitoring of soil carbon ecological processes in meadows under cold climates at high altitudes.