Comment on “Determining soil carbon stock changes: Simple bulk density corrections fail” [Agric. Ecosyst. Environ. 134 (2009) 251–256

Abstract

Lee et al. (2009) showed the equivalent soil mass (ESM) approach for correcting bulk density changes when estimating soil carbon stock or density. The ESM approach from Ellert and Bethany (1995) attempts to correct for differences in bulk density from different sampling dates by calculating the mass of soil C in an equivalent soil mass per unit area. This is done by first designating the mass of the heaviest soil layer as the equivalent mass. The C density from subsequent sampling is then calculated by estimating the thickness of the deepest soil layer required to attain the equivalent mass. Lee et al. (2009) showed various calculations of the ESM approach. In this comment, we should like to point out that the material coordinate system, which is simpler andmore general, is better for handling this issue. In fact, Gifford and Roderick (2003) have proposed the use of the mass (or material) coordinate system for soil C accounting. The material coordinate or Lagrange system was proposed by Smiles and Rosenthal (1968) for calculating water flux in swelling soils. It has been applied in calculatingwater flows in swelling soils (McGarry and Malafant, 1987; Ringrose-Voase et al., 2000).For C accounting, we based the C density on the mass of the soil mineral material. First, we calculate the mineral mass of each sampling