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Abstract
This study was conducted to derive point pedotransfer functions (PPTFs) for soil water retention (SWR) in western Iran. Topsoil and subsoil of 63 soil series, which were representative of different regions of Hamadan province, were sampled. Soil water retention was determined by the sand box and pressure plate at matric suctions (h m) of 0, 1, 2, 5, 10, 25, 50, 100, 200, 500, 1000 and 1500 kPa. PPTFs were derived through multiple linear regressions for the topsoils and subsoils. These used particle size distribution, bulk density, organic matter, calcium carbonate and gravel contents as easily-available inputs. To increase the accuracy of the PPTFs, saturated water content was also included as an input variable in a group of PPTFs but they are not better as assessed using the Akaike Information Criterion. All of the PPTFs were statistically significant (p < 0.001) and could be used to predict the SWR. The absolute effect of bulk density on the SWR diminished as h m increased. Bulk density decreased the SWR for low h m and increased it for high h m. In the wet range, organic matter increased the SWR. Clay and silt increased SWR whereas gravel decreased it. The effect of calcium carbonate on SWR was negligible.
Acknowledgement
Appreciation is expressed to Deputy of Research Affairs, Bu-Ali Sina University, Hamadan for the financial support of this project. Special appreciation is extended to Prof. A.R. Dexter of Institute of Soil Science and Plant Cultivation (IUNG-PIB), Poland and Dr. A.A. Sabziparvar of Bu-Ali Sina University for their thoughtful reviewing of the manuscript and helpful comments. We also would like to acknowledge the comment of a reviewer who suggested using the Akaike Information Criterion to compare different pedotransfer functions.
