A critique of soil carbon assumptions used in ILUC modeling
Recent estimates of land use change emissions vary widely, in part due to differences in assumptions on soil carbon. In this report, we review a recent meta-analysis on soil carbon changes with land conversion and discuss its results in the context of the underlying literature studies it references. In particular, we assess how the conversion of cropland to corn affects soil carbon stocks.
We assess the data input related to soil carbon changes under corn, based on a 2015 meta-analysis by Argonne National Laboratory (ANL). We identify three main questions related to the application of the results of the meta-analysis within the ANL land use change modeling framework: (a) lack of comparison with other crops; (b) use of data from crop rotational systems; and (c) influence of short-term studies.
Overall, we do not believe that this meta-analysis adequately supports an assumption that the conversion of generic cropland to corn will increase soil carbon. The scientific literature points towards a consensus that continuous corn cultivation does not significantly affect soil carbon stocks over time, and there is not sufficient evidence to compare soil carbon under corn with that under other annual food crops. Assuming that soil carbon stocks increase when other crops are converted to corn would tend to underestimate land use change impacts from corn ethanol.