Large uncertainty in soil carbon modelling related to method of calculation of plant carbon input in agricultural systems

Summary

This comparative analysis demonstrates that the choice of allometric equation used to estimate soil carbon inputs from crop residues introduces substantial uncertainty into dynamic soil carbon models, with estimated inputs varying by up to 6.6 Mg C ha⁻¹ year⁻¹ for individual crops. Applied to a Swiss long-term cropping experiment across 28 years and multiple fertiliser treatments, the five equations tested produced annual soil carbon input estimates ranging from 2.1 to 5.3 Mg C ha⁻¹, with significant downstream effects on simulated soil organic carbon stocks. The authors conclude that critical evaluation and selection of allometric equations and their coefficients is essential when developing model-based soil carbon inventories for agricultural systems.

UK applicability

The findings highlight a critical methodological uncertainty relevant to UK greenhouse gas inventory reporting and soil carbon accounting under environmental schemes. Given regional differences in crop types, yields and growing conditions, UK applications would require validation of suitable allometric equations for British agricultural conditions before adoption in policy-relevant carbon modelling.

Key measures

Soil carbon inputs (Mg C ha⁻¹ year⁻¹) estimated via five allometric equations; simulated soil organic carbon stocks using C-TOOL model; variation in estimates by crop type and yield level

Outcomes reported

The study compared five allometric equations used to calculate soil carbon inputs from crop yields in a 28-year Swiss field experiment, finding estimated annual inputs ranged from 2.1 to 5.3 Mg C ha⁻¹ year⁻¹ across equations. Soil carbon stock simulations using the C-TOOL model showed that choice of allometric equation strongly affected predicted soil organic carbon trajectories, with four equations predicting SOC decline and one predicting no change.

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