Summary
This paper quantifies substantial uncertainty in soil carbon modelling that arises specifically from the choice of allometric equation used to estimate carbon inputs from crop residues, rather than from model structure or parameters alone. Using 28 years of data from a Swiss long-term cropping experiment across four fertiliser treatments, the authors demonstrate that the same yield data produce carbon input estimates ranging from 2.1 to 5.3 Mg C ha⁻¹ year⁻¹ depending on equation selection, with consequent dramatic differences in modelled SOC trajectories. The work highlights that standardising and validating allometric equations is a critical—and currently overlooked—step in establishing reliable soil carbon inventories for agricultural greenhouse gas reporting.
UK applicability
The methodological findings regarding allometric equation selection are directly applicable to UK soil carbon modelling for inventory and policy purposes, though the specific equations evaluated were derived from European data and UK conditions may require equation validation or development. The identification of carbon input estimation as a major source of uncertainty is likely to be relevant for UK agricultural carbon accounting frameworks and long-term field studies.
Key measures
Annual soil carbon inputs (Mg C ha⁻¹ year⁻¹), modelled soil organic carbon (SOC) stock changes, variation in estimates across five allometric equations, range of uncertainty by crop type and yield level
Outcomes reported
The study compared five allometric equations for calculating soil carbon inputs from crop yields and assessed how equation choice affects modelled soil organic carbon stocks using the C-TOOL model. Estimated annual soil carbon inputs ranged from 2.1 to 5.3 Mg C ha⁻¹ year⁻¹ across equations, with simulations showing either SOC stock decreases or no change depending on which equation was used.
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