Elsevier

Geoderma

Volumes 221–222, June 2014, Pages 20-27
Geoderma

A test of the Beerkan Estimation of Soil Transfer parameters (BEST) procedure

https://doi.org/10.1016/j.geoderma.2014.01.017Get rights and content

Highlights

  • BEST is attractive for a simple soil hydraulic characterization.

  • An applicative procedure yielding reliable water retention estimates was developed.

  • The unsaturated soil conductivity was affected by the assumption of a unimodal model.

  • Factors needing developments and improvements were identified.

  • A joint effort of the scientific community would be advisable to improve BEST.

Abstract

The Beerkan Estimation of Soil Transfer parameters (BEST) procedure is attractive for a simple soil hydraulic characterization but testing the ability of this procedure to estimate soil properties is necessary. The BEST predictions were compared with soil water retention and hydraulic conductivity data measured in the laboratory and the field, respectively, at ten Sicilian field sites. Provided that BEST yielded physically possible scale parameters of the soil characteristic curves in most of the four replicated infiltration runs at a site, the measured water retention was satisfactorily predicted (i.e., not statistically significant differences between measurements and predictions, significant correlation between the data, regression line not significantly different from the identity one) when i) the infiltration run was relatively short (11 applied volumes of water); ii) the n shape parameter of the water retention curve was estimated on the basis of the measured sand and clay content of the soil; and iii) the saturated soil water content, θs, was set equal to 93% of the porosity. Possible field saturated soil hydraulic conductivity values were also obtained, although some trace of soil disturbance by the infiltration run was detected. The predicted unsaturated soil hydraulic conductivity was higher than the measured one, probably because the unimodal hydraulic conductivity function used in BEST does not reproduce the changes in the pore system of a real soil in the pressure head range close to saturation. It was concluded that BEST is promising to simply yield a reasonably reliable soil hydraulic characterization. An improved description of the unsaturated hydraulic conductivity function is desirable.

Introduction

Determining the relationships between soil water pressure head, h, volumetric water content, θ, and hydraulic conductivity, K, allows us to interpret and numerically simulate soil hydrological processes. These hydraulic characteristic curves are generally determined with laboratory and field methods differing by accuracy and experimental efforts.

Lassabatère et al. (2006) proposed to estimate the θ(h) and K(θ) curves with the Beerkan Estimation of Soil Transfer parameters (BEST) procedure, using an infiltration experiment in the field with a zero pressure head on a circular soil surface and a few basic soil physical determinations (particle size distribution, PSD, bulk density, and initial and final water content).

BEST is receiving increasing attention by the scientific community since it allows an experimentally simple hydraulic characterization of unsaturated soils. For example, Mubarak et al. (2009a) used the Beerkan infiltration method to characterize temporal variability of soil hydraulic properties under high-frequency drip irrigation, and Mubarak et al. (2009b) used the collected data to decide whether or not the changes in the topsoil parameters over the course of a cropping season should be taken into account to simulate water transfer processes. Mubarak et al. (2010) used the Beerkan method to review the soil hydraulic properties of the field sampled in 1990 by Vauclin et al. (1994), after 17 years of repeated agricultural practices. Lassabatère et al. (2010) used BEST to study the effect of sediment accumulation on the water infiltration capacity of two urban infiltration basins located on two different subsoils. Gonzalez-Sosa et al. (2010) applied BEST to document the spatial variability of the water retention and soil hydraulic conductivity curves within a watershed of 7 km2. A characterization of the unsaturated hydraulic properties of basin oxygen furnace slag based on Beerkan water infiltration experiments was carried out by Yilmaz et al. (2010). The hydraulic properties of some Burundian soils, that are difficult to characterize with other laboratory and field experimental procedures, were determined by Bagarello et al. (2011).

Investigations focused on BEST procedures were also carried out. They include, for example, the estimation of the water retention shape parameter (Minasny and McBratney, 2007), the fitting accuracy of the BEST PSD model to the data (Bagarello et al., 2009a), the algorithm to analyze the infiltration data (Yilmaz et al., 2010) and the constraint on the duration of the infiltration run (Bagarello et al., 2011). More recently, Xu et al. (2012) suggested that the applicability of the method may become questionable in wet conditions, due to a poor fitting performance of the cumulative infiltration curve. Bagarello and Iovino (2012) suggested that determining the soil textural characteristics before the BEST experiment may be an effective means to preliminarily establish if the expected performances of the water retention and particle size models are good or there is the possibility of a poor description of the water retention data. These authors also suggested that, for a general use of BEST, the Minasny and McBratney (2007) procedure should be preferred to estimate the water retention shape parameter as compared with other procedures, including the original one. It should be noted that field validation of BEST was not carried out by Bagarello and Iovino (2012) since these authors focused their investigation on the reliability of the pedotransfer model used by BEST to estimate the water retention curve. According to Nasta et al. (2012), the tortuosity parameter, p, is relatively insignificant compared to the β and γ infiltration constants that should be specifically calibrated for each soil type.

The large interest for the BEST procedure justifies comparisons of the predicted soil properties with independent measurements, i.e. with soil data collected by other experimental methods. These comparisons are important for many reasons. The most obvious is to establish if the simplified method is a practical alternative to more cumbersome and time consuming methods. Another reason is that they allow the detection of points in the indirect procedure needing specific adjustments or developments. For example, the duration of the infiltration run is an issue to be considered taking into account that a long run can theoretically be expected to yield a more reliable estimate of steady-state infiltration rate than a short run at the expense, in practice, of more appreciable deterioration phenomena of the infiltration surface. An extensive assessment of the BEST predictions against alternative methods has still to be carried out, although some contributions can now be found in the literature. For example, field and laboratory measurements of saturated soil hydraulic conductivity were generically found to be of the same order of magnitude in the investigation by Yilmaz et al. (2010).

The objective of this investigation was to test the applicability of the BEST procedure at the near point scale, i.e. within an area of a few square meters, in different Sicilian soils. At this aim, the predicted soil hydraulic parameters were used to establish a comparison with laboratory measured water retention data and field measured saturated and unsaturated soil hydraulic conductivities.

Section snippets

Field sites, soil sampling and soil parameter calculations

Ten sites located in western Sicily, showing appreciable differences in both soil texture and land use (Table 1), were sampled in the second half of 2010.

For a given site, having an area of approximately 25 m2, eight undisturbed soil cores (0.05 m in height by 0.05 m in diameter) were collected at the 0 to 0.05 m and 0.05 to 0.10 m depths in four randomly selected points. Four disturbed soil samples (0–0.10 m depth) were also collected. The undisturbed soil cores were used to determine in the

Results and discussion

The two applied procedures to determine the n parameter (Lassabatère et al., 2006, Minasny and McBratney, 2007) yielded significantly correlated values (R2 = 0.88, R > 0, N = 10) that were generally higher with the Minasny and McBratney (2007) procedure (Fig. 1). However, the 95% confidence intervals for the intercept (− 0.112–0.949) and the slope (0.569–1.066) suggested a statistical coincidence of the regression line with the identity one.

For both the long (L) and short (S) infiltration runs, the

Conclusions

In this investigation, the soil of ten Sicilian sites was characterized at the near point scale by replicating all measurements four times for a given site.

The duration of the infiltration run, the assumed saturated soil water content, θs, and the calculation procedure of the n shape parameter of the water retention curve influenced the water retention predictions by the Beerkan Estimation of Soil Transfer parameters (BEST) procedure of soil hydraulic characterization. A good correspondence of

Acknowledgments

This study was supported by grants of the Università degli Studi di Palermo (fondi ex 60%, Dottorato di Ricerca in Sistemi Agro-Ambientali, indirizzo Idronomia Ambientale) and the Sicilian Region (Progetti DIFA and CISS). Thanks to M. Birtone, S. Pomilla, and S. Sferlazza for their help in the experimental work. Vincenzo Bagarello and Massimo Iovino outlined the investigation and Simone Di Prima analyzed the data. All authors contributed to analyze and discuss the results and write the

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