『Abstract
Use of a single factor for converting soil organic carbon to
soil organic matter is challenged. The basis for this challenge
arises from four sources: the original papers published in the
nineteenth century, empirical studies published throughout the
twentieth century, theoretical considerations of organic matter
composition, and a consideration of what led to the popularity
and general acceptance of the conventional factor. The conventional
factor of 1.724, based on the assumption that soil organic matter
contains 58% carbon, applies only to some soils or only to particular
components of soil organic matter. Studies published since the
end of the nineteenth century have consistently shown that the
factor of 1.724 is too low for most soils. In a review of previously
published data, the median value for the conversion factor was
found to be 1.9 from empirical studies and 2 from more theoretical
considerations. A factor of 2, based on the assumption that organic
matter is 50% carbon, would in almost all cases be more accurate
than the conventional factor of 1.724. A consideration of the
possible variation in organic matter composition predicts a range
of factor values between 1.4 and 2.5, a range that is narrower
than empirical results at least in part because of the interaction
between the methods used to estimate organic matter and soil composition.
Convenience. authority, and tradition rather than strength of
evidence are in large part responsible for the widespread acceptance
of the conventional factor.
Keywords: Van Bemmelen factor; Soil organic carbon; Soil organic
matter; Humic substances; Organic carbon storage』
Contents
1. Introduction
2. Establishment of the conventional factor
3. Challenges to the conventional factor
4. A comparison of theoretical estimates with empirical observations
5. Sources of variation
6. Persistence of the conventional factor
7. Conclusion
Acknowledgements
References