Reevaluating multi-pool first-order kinetic models for fitting soil incubation data

• Reevaluate suitability of first-order kinetics with constant rate parameters for incubation data. • Solely fitting cumulative C effluxes may cause a biased understanding. • Suggest focusing more on instantaneous rather than cumulative C effluxes for accurate modeling C dynamics. Soil incubation experiments are frequently conducted to investigate soil carbon (C) cycling and its response to environmental changes. Multi-pool first-order models, which apply constant kinetic rate parameters for each pool, are widely used for fitting these datasets due to their simplicity. However, their ability to accurately represent instantaneous C effluxes is often overlooked, as cumulative effluxes are typically prioritized. Here, we calibrated a three-pool first-order model using a 384-day incubation dataset with fluctuating CO 2 and CH 4 effluxes. Despite constantly good performance for cumulative C effluxes ( R 2 = 0.99–1.00), the R 2 values vary greatly with experimental conditions for instantaneous effluxes ( R 2 = 0.36–0.93), depending on the frequency of aerobic-anaerobic shifts. The results are regardless of the objective function used for model fitting (i.e., maximizing R 2 for instantaneous or cumulative C effluxes). Compared to cumulative effluxes, we propose emphasizing instantaneous effluxes and calibrating additional variables in soil C modeling. This strategy can offer more insights for improving predictions and enhancing understanding of soil C-climate feedbacks under dynamic environmental conditions.