Summary
This study evaluated the critical role of allometric equation selection in estimating soil carbon inputs from agricultural crop residues, a fundamental input to dynamic soil carbon models used in greenhouse gas inventories. Using 28 years of data from a Swiss long-term cropping experiment, the authors demonstrated that choice of equation alone could cause modelled soil organic carbon stocks to decline under one method whilst remaining stable under another, with differences between equations reaching 6.6 Mg C ha⁻¹ year⁻¹ for individual crops. The findings highlight that uncertainty in model-based soil carbon inventories stems substantially from allometric coefficient selection, not merely from model parameters or structure.
UK applicability
The methodology and findings are directly relevant to UK soil carbon accounting, particularly for agricultural greenhouse gas inventories and carbon sequestration policy. UK modellers should evaluate whether allometric equations developed for Swiss or other European conditions are appropriate for British crop types and climates, or whether equation recalibration is necessary to avoid similar uncertainties in national carbon reporting.
Key measures
Annual soil carbon inputs (Mg C ha⁻¹ year⁻¹); simulated soil organic carbon stocks (SOC); comparison of five allometric equations; variation across crop types and fertiliser treatments
Outcomes reported
The study compared five allometric equations used to calculate soil carbon inputs from crop yields and quantified the resulting uncertainty in soil organic carbon stock predictions 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 simulated soil carbon stocks showing either decline or stability depending on which equation was selected.
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