MODELING TEMPERATURE AND MOISTURE EFFECTS ON C-N TRANSFORMATIONS IN SOILS - COMPARISON OF 9 MODELS

Most models designed to simulate carbon and nitrogen transformations i n the soil have defined functions to describe the effects of temperatu re and water content on microbial processes. These functions are norma lly derived from soil incubation studies, but they could be one of the main differences among models, and their specific effect has yet to b e studied. We have analysed different functions describing the effects of soil moisture, temperature and their interaction on microbial proc esses reported in the literature. Evolution of temperature (f(T)) and moisture (g(psi)) functions applied to N mineralisation in nine C-N si mulation models (SOILN, MATHILD, SUNDIAL, TRITSIM, DAISY, NLEAP, NCSOI L, CANTIS and Kersbaum's), representing a wide range of those reviewed , were compared by using a daily data set of soil temperature (T) and water potential (Psi) obtained in the held in Northern France. Compari son between f(T) and g(psi) was realised using a common values of 'ref erence' temperature and moisture (T-ref and Psi(ref)), values at which f(T), and g(psi) are equal to 1 in all models. Large differences were observed among proposed f(T) especially when T-ref = 35 degrees C, wh ich is much higher than the average temperature of data set examined ( T = 11 degrees C). In this case, maximal relative differences between f(T) functions of studied models were around 325%. The g(psi) function s reached similar maximum values at soil moisture near held capacity, except for NLEAP and NCSOIL models. In the dry range of soil moisture, the relative differences in g(psi) become higher. The combined effect of temperature and moisture product, f(T).g(psi), varied by a five-fo ld factor between models for T-ref= 35 degrees C and Psi(ref)= -50 kPa . (C) 1997 Elsevier Science B.V.