Assessment of the Methods of Estimating Scaling Parameter in Arya-Paris Model for Predicting Soil Water Retention Curve

Document Type : Research Paper

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Abstract

Direct measurement of soil water retention curve parameters is hard, costly, and sensitive. One of the good indirect methods in prediction of soil water retention curve is Arya-Paris model, which uses the soil particle size distribution (PSD) data. The AP model estimates pore radius ( ri ) from the radius (Ri) of spherical particles by scaling pore with a parameter α. In this study, data from soil particle-size distribution, soil water retention curve, bulk density, and porosity of 96 different soils including sandy, loamy sand, sandy loam, and silty loam were used to help assessing methods of estimating the scale parameter. The values of scaling parameter obtained from the inverse method for the sandy, loamy sand, sandy loam, and silty loam were 1.32, 1.36, 1.45, and 1.23, respectively. Use of  the linear method for sandy and silty loam soils resulted in α values of 1.34 and 1.25, respectively, while, by using the constant method (recommended by Arya et al) for sandy loam and loamy sand, α values were1.37 and 1.46, respectively, which were the closest to the real calculated values. By studying the variations of α in different soil textures and moisture contents, it was noted that there was no significant relationship between α and the amount of sand in the soil. However, increase in the soil moisture increased the value of α while the correlation coefficient for α and soil moisture was calculated at 0.45.

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Journal of Water Research in Agriculture
Volume 27, Issue 3
April 2013
Pages 347-356

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