Modelling temperature and moisture effects on C–N transformations in soils: comparison of nine models

Most models designed to simulate carbon and nitrogen transformations in the soil have defined functions to describe the effects of temperature and water content on microbial processes. These functions are normally derived from soil incubation studies, but they could be one of the main differences among models, and their specific effect has yet to be studied. We have analysed different functions describing the effects of soil moisture, temperature and their interaction on microbial processes reported in the literature. Evolution of temperature (fT) and moisture (gΨ) functions applied to N mineralisation in nine C–N simulation models (soiln, mathild, sundial, tritsim, daisy, nleap, ncsoil, cantis and Kersbaumʹs), representing a wide range of those reviewed, were compared by using a daily data set of soil temperature (T) and water potential (Ψ) obtained in the field in Northern France. Comparison between fT and gΨ was realised using a common values of `referenceʹ temperature and moisture (Tref and Ψref), values at which fT and gΨ are equal to 1 in all models. Large differences were observed among proposed fT, especially when Tref=35°C, which is much higher than the average temperature of data set examined (T=11°C). In this case, maximal relative differences between fT functions of studied models were around 325%. The gΨ functions reached similar maximum values at soil moisture near field capacity, except for nleap and ncsoil models. In the dry range of soil moisture, the relative differences in gΨ become higher. The combined effect of temperature and moisture product, fT·gΨ, varied by a five-fold factor between models for Tref=35°C and Ψref=−50 kPa.