Adding an empirical factor to better represent the rewetting pulse mechanism in a soil biogeochemical model

The rewetting of a dry soil causes a pulse in decomposition of soil organic matter (SOM). This mechanism may dominate carbon (C) and nitrogen (N) cycles in arid, semi-arid and Mediterranean ecosystems. Existing biogeochemical models perform poorly for systems characterized by pulsed events. In this study, we added a rewetting factor into the DAYCENT soil biogeochemical model to better represent the drying-rewetting pulses. Based on a 4-month laboratory incubation from a parallel study, we developed a simple rewetting factor for representing the enhanced mineralization pulse by rewetting stimulation. The rewetting factor was then incorporated into DAYCENT by modifying the soil moisture factor. The DAYCENT modification significantly improved model performance in predicting soil C respiration rates in drying-rewetting treatments through the capture of rewetting pulses. The modification also improved prediction performance for net N mineralization in treatments with shorter rewetting intervals, but did not improve predictions in treatments with longer rewetting intervals. The model modifications were validated by using a laboratory incubation data set from a different field site. The modified DAYCENT predictions showed that active and slow SOM pools were major contributors to mineralization pulses while the contribution from the passive pool was minimal. The modifications we made improved model performance and should be considered in future field representations of biogeochemical processes.