Assessing Soil Moisture Regimes with Traditional and New Methods

Soil moisture regime classes are required by U.S. soil taxonomy and other classification systems. Soil moisture regimes are based on long-term daily data of soil water content, which are as a rule estimated by means of models. International Commitee on Soil Moisture and Temperature Regimes (ICOMMOTR) has proposed classifying pedoclimate on the basis of biweekly water potential. This study was conducted to validate the use of the Erosion-Productivity Impact Calculator (EPIC) model in assessing soil water content of experimental fields placed in different European pedoclimatic conditions, to compare the pedoclimatic classification obtained with EPIC with those produced by the traditional Billaux and Newhall models, and to evaluate the results attained with the ICOMMOTR methodology. The trial was carried out over a 5-yr period in four experimental farms. The soil water content of a meadow was measured weekly or biweekly, at 0.15- and 0.75-m (or 0.45-m) depths. The EPIC model results were compared with measured data and submitted to statistical analysis of accuracy. Predicted daily soil water from EPIC was utilized to classify the soil moisture regimes following the requirements of U.S. soil taxonomy. The traditional Billaux methodology led to an overestimation of the presence of the xeric class whereas the Newhall method overrated the ustic soil moisture regime. The ICOMMOTR classification methodology was less affected by crop and by year variability than all the other methods and performed better in differentiating the soil moisture regimes of the four study sites.