Experimental corrections of simplified methods for predicting water retention curves in clay-loamy soils from particle-size determination

The Arya and Paris model for predicting soil water retention curves from particle-size distribution data is a commonly accepted method for rigid soils with medium grain size but limitations to its application for fine textured soils occur, due to the dominant role of internal structure in such soils. Moving from the consideration that simplified models for determining soil hydraulic characteristics may be usefully adopted to reduce laboratory investigation costs, in this study an attempt is made to extend the Arya-Paris formulation to clay-loamy soils by means of an experimental calibration function which takes into account the effective soil water retention behaviour. The methodology is based on an inversion procedure of the Arya-Paris model from observed values of water retention and potential during evaporation processes on undisturbed soil columns. It has been found that the resulting calibration function is typical for each soil and it substantially improves the prediction of the soil water retention curve from textural information.