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Deriving and Validating Pedotransfer Functions for Some Calcareous Soils ⇑ Habib Khodaverdiloo A, Mehdi Homaee B, , Martinus Th

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Deriving and Validating Pedotransfer Functions for Some Calcareous Soils ⇑ Habib Khodaverdiloo A, Mehdi Homaee B, , Martinus Th Journal of Hydrology 399 (2011) 93–99 Contents lists available at ScienceDirect Journal of Hydrology journal homepage: www.elsevier.com/locate/jhydrol Deriving and validating pedotransfer functions for some calcareous soils ⇑ Habib Khodaverdiloo a, Mehdi Homaee b, , Martinus Th. van Genuchten c, Shoja Ghorbani Dashtaki d a Department of Soil Science, Urmia University, Urmia, Iran b Department of Soil Science, Tarbiat Modares University, Tehran 14115-336, Iran c Department of Mechanical Engineering, COPPE/LTTC, Federal University of Rio de Janeiro, Rio de Janeiro, RJ, Brazil d Department of Soil Science, Shahrekord University, Shahrekord 88186/34141, Iran article info summary Article history: The unsaturated soil hydraulic properties are needed for many different applications in soil hydrology. Received 12 January 2010 Pedotransfer functions (PTFs) have proven to be useful to indirectly estimate these parameters from more Received in revised form 14 December 2010 easily obtainable soil data. Until now no studies have been conducted to derive or verify PTFs for calcar- Accepted 28 December 2010 eous soils, which hydraulically may not behave the same as non-calcareous soils. The objectives of this Available online 6 January 2011 study were to assess the influence of soil CaCO3 on the soil water retention characteristics of some cal- This manuscript was handled by P. Baveye, careous soils, and to derive PTFs for these soils. Two data sets were used to derive and evaluate the estab- Editor-in-Chief lished PTFs. Data set 1 containing 220 samples was employed as a calibration set for multiple linear regression. An independent data set containing 55 soil samples from a different location served to verify Keywords: the derived PTFs. No significant difference in accuracy was found between the PTFs with and without Calcareous soils CaCO3 in terms of estimating specific soil water retention values or the van Genuchten soil hydraulic Pedotransfer function parameters. Compared with the Rosetta PTFs of Schaap et al. (2001), the derived point and parametric Soil hydraulic properties PTFs provided better accuracy with average RMSE values of 0.028 and 0.107 cm3 cmÀ3, respectively. Water retention curve Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction content. From a prediction point of view, PTFs can be distinguished into point and parametric PTFs. Point PTFs predict the water Estimates of the unsaturated soil hydraulic properties are content at pre-defined soil water pressure heads, while parametric needed for many agronomic, environmental and engineering appli- PTFs assume that the hydraulic properties can be described ade- cations involving water flow and contaminant transport processes quately with a hydraulic model containing a limited number of in the vadose zone. A broad array of laboratory and field methods parameters. are currently available for direct measurement of the hydraulic Iran, as many other countries, does not have sufficient soil properties (e.g., Dirksen, 2000; Dane and Topp, 2002). Unfortu- hydraulic data for deriving local PTFs for relevant agricultural or nately, most or all methods are too time consuming and costly environmental modeling applications. However, several large dat- for most applications (Wösten et al., 2001). Furthermore, due to abases such as UNSODA (Leij et al., 1996), HYPRES (Lilly, 1997; high temporal and spatial variability in the hydraulic characteris- Wösten et al., 1999), WISE (Batjes, 1996) and the USDA-NRCS ped- tics, a large number of samples is generally required to accurately on soil characterization database (Soil Survey Staff, 2010a) have characterize field conditions. been established to facilitate analyses of the soil hydraulic proper- An alternative to direct measurement is the use of indirect ties. Consequently, it is attractive to use such databases to develop methods in which the hydraulic properties are estimated from PTFs for regions with less available data. Although the advantages more easily measured or more readily available soils data (Bouma, of existing PTFs are well discussed in the literature (e.g. Tietje and 1989; Wösten et al., 2001). Methods that may be used for this Tapkenhinrichs, 1993; Espino et al., 1995; Wösten et al., 1995; purpose include statistical pore-size distribution models, inverse Minasny et al., 1999), their applicability to calcareous soils has models and especially pedotransfer functions (PTFs). PTFs (Bouma not been addressed thus far (Homaee and Farrokhian Firouzi, and van Lanen, 1987; Bouma, 1989) are based on the premise that 2008). Also, practical applications of most PTFs is often hampered the hydraulic properties can be related to basic soil properties such by their very specific data requirements. as the particle size distribution, bulk density and/or organic matter Hydrologists in countries with insufficient soil hydraulic or taxonomic data are often confronted with situations where one or more PTF input parameters is not available. The Rosetta package ⇑ Corresponding author. Tel.: +98 21 4829 2280; fax: +98 21 4419 6524. (Schaap et al., 2001) implements five hierarchical PTFs to predict E-mail address: [email protected] (M. Homaee). the WRC, as well as the saturated and unsaturated hydraulic 0022-1694/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jhydrol.2010.12.040 94 H. Khodaverdiloo et al. / Journal of Hydrology 399 (2011) 93–99 conductivity. The hierarchy in PTFs allows prediction of van the core. This procedure was carried out over a period of 2 days to Genuchten hydraulic parameters and the saturated hydraulic con- obtain as complete saturation as possible by minimizing entrapped ductivity using limited (soil textural class only) to more extended and dissolved air in the cores. Soil water contents at saturation (texture, bulk density, and one or two water retention points) in- were determined by oven-drying the saturated samples at 105 °C put data. This makes Rosetta quite useful for countries having data for 24 h. After saturation, cores were placed on a saturated ceramic limitations. plate inside a pressure plate apparatus and subjected to consecu- Calcareous soils are widely distributed over the world and tive pressure heads of À100, À330, and À1000 cm to allow desat- physically may not behave the same as non-calcareous soils. Cal- uration of the samples and measurement of the water content. Soil careous soils contain 5% or more (by volume) inorganic carbon or water retention values at À3000, À5000, and À15,000 cm pressure CaCO3 equivalent (Soil Survey Staff, 1999). Soils of this type are heads were similarly determined using a pressure plate apparatus the dominant formation in many areas, particularly in arid and on disturbed soil samples in three replicates. semiarid regions. According to the FAO, about 65% of soils in Iran Particle size distributions of selected soil samples (ranging from are calcareous (FAO/UNDP, 1972). Inorganic carbon in soils com- those having the lowest to the highest CaCO3 contents) were deter- monly exists in the form of the carbonate minerals calcite (CaCO3), mined after removing their calcium carbonate. Calcium carbonate dolomite [Ca, Mg(CO3)2], and as magnesium calcites (Ca1Àx was removed using diluted HCl following procedures proposed MgxCO3). Other less common forms are aragonite (CaCO3) and sid- by Kroetsch and Wang (2006) for removal of carbonates prior to erite (FeCO3). Carbonates in soils may be of primary (inherited determining particle size distributions. The HCl-treated soil from parent materials) or secondary (pedogenic) origin. Secondary samples were air-dried and grinded, after which the particle carbonates usually consists of aggregates made up of silt- and clay- size distributions and water retention values at À3000, À5000, sized calcite crystals, which are easily identified using grain mount and À15,000 cm pressure heads were obtained, again using the techniques. Large crystals of calcite or dolomite are mostly of pri- pressure plate apparatus. A t-test was performed to verify statisti- mary origin (Doner and Lynn, 1989). cal differences between the amounts of retained water and the soil Qualitative and quantitative knowledge of Ca and Mg carbonates particle size distributions of paired samples (i.e., samples before is useful in many agronomic and environmental studies, such as for and after calcium carbonate removal). investigations of root growth, water movement, contaminant trans- To obtain a uniform description of all WRCs, we used the soil port, soil pH (Nelson, 1982) and the nature of the exchange complex water retention equation of van Genuchten (1980): (Goh and Mermut, 2006). Studies that considered the effects of cal- h À h cium carbonate precipitation on reductions in pore space suggest h h h s r 1 ð Þ¼ r þ n 1À1=n ð Þ that neither water retention nor the hydraulic conductivity is af- ð1 þjahj Þ fected significantly by calcium carbonate precipitation (Frenkel where h is the volumetric water content (–), h is the soil water pres- et al., 1978). However, from water retention and adsorption energy sure head (L), hr and hs are the residual and saturated water contents points of view, carbonates of the clay size can be treated as silt par- (–), respectively, and a (LÀ1) and n (–) are shape factors. The nonlin- ticles (Soil Survey Staff, 2010b). Thus, the hydraulic properties of ear least-squares optimization program RETC of van Genuchten calcareous soils may well differ from non-calcareous soils. Also, cal- et al. (1991) was used to fit the hydraulic parameters in Eq. (1) to cium carbonate is routinely removed from soil when soil texture is the measured retention data. determined. The properties of soils with large CaCO3 contents hence The geometric mean dg (L) and geometric standard deviation dg may well change during standard hydraulic analyses, which may (–) of the soil particle diameters were determined using methods further complicate the use of PTFs for non-calcareous soils. Hence, proposed by Shirazi and Boersma (1984): the applicability of available PTFs, such as those in the Rosetta pack- age, to calcareous soils remains largely untested.
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