Romul_Hum model of soil organic matter formation coupled with soil biota activity. III. Parameterisation of earthworm activity

Quantitative description of the role of soil fauna in soil organic matter (SOM) formation and dynamics is necessary for further development of SOM modelling. This is especially true for the role of anecic earthworms in SOM formation, which was first observed in the classical investigations of Charles Darwin in 1881. Despite the large number of earthworm studies available in the literature, more attention has been paid to the role of these organisms in loss of carbon through decomposition and nutrient release than to their role in SOM formation. A set of anecic earthworm parameters were compiled or developed for ease of incorporation as a module into the SOM dynamics model Romul_Hum, which also represents the SOM forming activities of soil micro- and meso-biota. An approach was developed for initialization of earthworm biomass in the absence of measured biomass, and parameters were developed for food palatability, ingestion and egestion. The eco-physiological parameters of food consumption, excretion efficiency, assimilation efficiency, lifespan, and mortality for anecic earthworms were developed using an approach similar to that for food web mesofauna in the Romul_Hum. Parameters for processes unique to freshly excreted casts were developed to include rapid mineralization of SOM and nitrogen, SOM formation, and high nitrogen fixation rates. The addition of the earthworm module to the Romul_Hum model allows assessment of the combined effects of earthworms cast production, and micro- and meso-faunal food web activity within the casts, on the formation of stable SOM.