Dry Combustion Carbon, Walkley–Black Carbon, and Loss on Ignition for Aggregate Size Fractions on a Toposequence

Abstract

Accurate and simple methods for determining soil organic carbon that do not involve the use of chemicals that damage the environment are required. Dry combustion carbon, Walkley–Black carbon, and loss on ignition (LOI) were determined on whole soils (<2000 µm) and aggregate size fractions (250–2000 µm, 53–250 µm, <53 µm) collected from a toposequence, part cropped and part under forest regrowth. For each group, the Walkley–Black correction factor averaged 1.2, which was less than the usually assumed factor of 1.3. Both temperature and sample weight had significant effects on LOI, but the former had a greater effect. There were strong correlations between LOI and dry combustion carbon for all aggregate size fractions. Highest coefficient of determination (R2=0.89–0.93) were obtained for 1‐g soil samples ignited at 375°C for 2 h; under these conditions, slopes and intercepts of the regressions of organic carbon on LOI were not significantly different among aggregate fractions.