Abstract

Xuejun Dong and Bob Patton

Soil water retention curves are essential for solving water flow problems, but direct measurement usually is laborious, time-consuming and expensive. Thus indirect methods using more easily measured soil properties are frequently used. The model of Arya and Paris (1981) [Soil Sci. Soc. Am. J., 45: 1023-1030] has been used widely to predict water retention curves based on particle-size distribution and bulk density. A major difficulty in the application of this model is determining the empirical parameter describing soil particle shape. Despite numerous efforts for alternative calibration of this parameter, the original Arya-Paris model remains pervasive and relevant for varying textured soils. We developed an easy-to-use spreadsheet-like Minitab macro to automate the parameter estimation for use with the Arya-Paris model. This method was tested on prairie soils from North Dakota, USA. Results showed that parameter estimation for soil water retention curves was improved by allowing both soil particle shape and particle density parameters to vary. The best estimates of shape factors varied from 1.08 to 1.44 and those for particle density ranged from 1500 to 2650 kg/m3 . The macro facilitates the rapid characterization of soil water retention relations and is applicable to other soil types.