Evaluating Loss-on-Ignition Method for Determinations of Soil Organic and Inorganic Carbon in Arid Soils of Northwestern China

There is a need for determinations of soil organic carbon (SOC) and inorganic carbon (SIC) due to increasing interest in soil carbon sequestration. Two sets of soil samples were collected separately from the Yanqi Basin of northwest China to evaluate loss-on-ignition (LOI) method for estimating SOC and SIC in arid soils through determining SOC using an element analyzer, a modified Walkley-Black method and a LOI method with combustion at 375 °C for 17 h and determining SIC using a pressure calcimeter method and a LOI procedure estimated by a weight loss between 375 to 800 °C. Our results indicated that the Walkley-Black method provided 99% recovery of SOC for the arid soils tested. There were strong linear relationships (r > 0.93, P < 0.001) for both SOC and SIC between the traditional method and the LOI technique. One set of soil samples was used to develop relationships between LOI and SOC (by the Walkley-Black method), and between LOI and SIC (by the pressure calcimeter method), and the other set of soil samples was used to evaluate the derived equations by comparing predicted SOC and SIC with measured values. The mean absolute errors were small for both SOC (1.7 g C kg−1) and SIC (1.22 g C kg−1), demonstrating that the LOI method was reliable and could provide accurate estimates of SOC and SIC for arid soils.