Precocious 19th century soil carbon science

Abstract Soil organic matter is important for nutrient exchange in the soil environment, carbon sink, and soil fertility. Soil scientists usually estimate the amount of organic matter in a soil from its carbon content using the 1.724 conversion factor. The origin of this conversion factor is conventionally attributed to Jacob Maarten Van Bemmelen, a Dutch chemist. In the early nineteenth century, science academies devoted considerable attention to understanding soil humus to increase agricultural productivity. Van Bemmelen investigated the fertility of soils for growing tobacco in Indonesia. Van Bemmelen's 1890 publication used the 1.724 factor for estimating humus content from elemental analysis of C concentration. A survey of the scientific literature from the same period indicated that Emil Wolff was the first to suggest the factor. This paper draws a brief historical summary of van Bemmelen's research on soil organic matter, and discusses the origin and use of the 1.724 factor using the scientific literature from 1900s to 1930s. The origin of the factor is contextualized with the emerging humus theory of the 19th century. Our study suggests that the factor has been erroneously attributed to van Bemmelen and widely used in English, French, Dutch, and German literature. The 1.724 factor was originally developed for the conversion of carbon to humic substances, which themselves do not have a clear definition. Many regional studies have indicated the inadequacy of the factor.