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SOIL PHYSICS

Hood Infiltrometer—A New Type of Tension Infiltrometer

^a Institute of Soil Science and Site Ecology, Univ. of Technology, Dresden, Germany
^b Umwelt-Geräte-Technik, Müncheberg, Germany

^* Corresponding author (kai.schwaerzel{at}forst.tu-dresden.de).

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION THEORY MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Disk infiltrometers are widely used to determine saturated and near-saturated soil hydraulic conductivity. Previous studies have recommended applying a high-permeability material to the undisturbed soil surface to establish a complete hydraulic bond between the disk and the infiltration surface. Other studies have shown that the use of the contact material affects the infiltration, and hence also the determination of saturated and near-saturated conductivity. In this study, we tested a new type of infiltrometer (that we call a hood infiltrometer), which might overcome these problems. Instead of requiring a disk and contact material, it places a water-filled hood, open side down, onto the soil surface. In this study, repeated hood and disk infiltrometer field tests in conjunction with time-domain reflectometry (TDR) measurements were performed at the same location to compare the performance of the two types of infiltrometer. Furthermore, we extracted undisturbed soil cores to measure the hydraulic functions in the lab. The measured hood and disk data were analyzed using Wooding's solution and by numerical parameter optimization technique using uni- and bimodal hydraulic functions. Running the disk infiltrometer with a contact layer provided saturated hydraulic conductivities that were 10 times smaller than corresponding values measured by the hood infiltrometer. We attributed these differences to smearing, sealing, and clogging of pores, which led to additional flow impedances in the soil surface layer. We were able to show, however, that the combined use of hood and disk infiltrometers in conjunction with TDR enabled hydraulic characterization of the soil from saturation to dry conditions.

Abbreviations: TDR, time-domain reflectometry

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION THEORY MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Soil hydraulic conductivity functions hinge on soil structure and, with decreasing water content, on soil texture. Renger et al. (1999) differentiated between two principal types of hydraulic conductivity curves. With the first type, the hydraulic conductivity remains constant from saturation up to the air-entry pressure of the soil. Soils of this type start to drain at pressure heads below the air-entry value, producing a dramatic decline in hydraulic conductivity (Fig. 1 ). This curve type is particularly characteristic of sandy soils or of soils with a coherent structure. The second curve type is common for soils with macropores. In such soils, the saturated hydraulic conductivity may be orders of magnitude higher than the conductivity of the same soil under a few centimeters of pressure head sufficient to drain the macropores (Fig. 1). Most soils show a hydraulic conductivity curve between the two types.

View larger version (16K): [in this window] [in a new window]   Fig. 1. Principal types of hydraulic conductivity functions (redrawn from Renger et al., 1999); h = supply pressure head.

Only a few studies have dealt with the influence of the contact material on disk infiltrometer measurements. Reynolds and Zebchuk (1996) have demonstrated that the pressure head at the soil surface and the pressure head at the membrane on the disk infiltrometer can vary considerably depending on the thickness, saturated conductivity, and air-entry value of the contact material, and on the flow rate out of the infiltrometer. Using Darcy's law, they calculated the pressure head applied on the soil surface with a degree of certainty similar to that provided by a Mariotte bubble tower. Everts and Kanwar (1993) compared disk infiltration measurements with ponded infiltrometer measurements taken at the same place and the same positive head. They found that disk infiltrometer measurements made through a 20-mm layer of sand were an order of magnitude less than ponded infiltration measurements. Contact material to moisten correctly might be another source of error in disk infiltrometer measurements. Close et al. (1998) have shown that a nonuniform wetting of the contact material at the membrane interface led to very erratic infiltration results. Some researchers have suggested that contact material may not be needed for a relatively smooth soil surface (e.g., Logsdon and Jaynes, 1993; Wang et al., 1998). At the same time, Bagarello et al. (2001) found 30% lower infiltration rates than those obtained when a layer of contact material was present. These differences might be relevant for some practical purposes, e.g., when infiltration and deep leaching of chemicals is predicted (Kung et al., 2005).

We tested the new UGT (Müncheberg, Germany) infiltrometer that uses a hood instead of a disk to connect it to the soil. The theory behind the new system is that it places a water-filled hood with its open side directly onto the soil surface, which is meant to eliminate the problems of the disk infiltrometers in establishing a hydraulic bond between the infiltrometer chamber and the soil. The aim of our study was to compare the performance of the two types of infiltrometers using a combination of field and laboratory tests as well as numerical studies.

	THEORY

TOP NOTES ABSTRACT INTRODUCTION THEORY MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Steady-State Flow from a Circular Source
In this study, analysis of disk and hood infiltrometer measurements is based on Wooding's (1968) solution for infiltration from a circular source with a constant pressure head at the soil surface. If the unsaturated hydraulic conductivity K(h₀) (cm d^–1) is given by an exponential function (Gardner, 1958)

[1]

where K_s (cm d^–1) is the saturated hydraulic conductivity and * (cm^–1) is the exponential slope, then the steady-state flow rate Q (cm³ d^–1) is given by

[2]

where r₀ is the disc radius (cm), h₀ is the applied pressure head (cm), and K(h₀) is the unsaturated hydraulic conductivity at pressure head h₀. Equation [2] can be solved for K(h₀) using multiple pressure heads for a given disk radius (Ankeny et al., 1991; Reynolds and Elrick, 1991; Jarvis and Messing, 1995). Equations [1] and [2] can be applied piecewise such that * is a constant in the interval between two successively applied pressure heads h_0(i) and h_0(i+1):

[3]

where n is the number of applied pressure heads used and the subscript notation i + denotes the estimated values of * at the midpoint between successive supply pressure heads. Rearranging Eq. [2] leads to

[4]

where the steady-state infiltration rates at the midway points between adjacent supply pressure heads h_0(i+1/2) are given by (Jarvis and Messing, 1995)

[5]

The saturated hydraulic conductivity K_s can be calculated from Eq. [1] using known values of h_0(i+1/2), K_i+1/2, and _i+1/2* as follows:

[6]

Numerical Model and Inverse Parameter Estimation Procedure
The governing flow equation for radially symmetric isothermal Darcian flow in a variably saturated isotropic rigid soil is described with the following form of Richards' equation (Warrick, 1992):

[7]

where is the volumetric water content (m³ m^–3), t is time (s), r is the radial coordinate (cm), h is the pressure head (cm), K is the hydraulic conductivity (cm d^–1), and z is the vertical coordinate (positive upward, cm). Equation [7] was numerically solved for the following initial and boundary conditions _i(z) using the HYDRUS-2D model (imnek et al., 1998):

[8]

[9]

[10]

[11]

where _i is the initial water content (m³ m^–3), h₀ is the time-variable supply pressure head imposed by the disk infiltrometer (cm), h_i is the initial pressure head (cm), and r₀ is the disk radius (cm). Equation [8] describes the initial condition in terms of the water content. Equation [9] specifies the time-variable pressure head below the disk and Eq. [10] prescribes a zero-flux condition at the remainder of the soil surface. Equation [11] states that the other boundaries are sufficiently distant from the infiltration source so that they do not influence the flow process. A no-flow condition was set at r = 0. In this study, the unimodal VGM model (van Genuchten, 1980; Mualem, 1976)

[12]

[13]

[14]

[15]

describes the soil hydraulic properties of Eq. [7], where S (dimensionless) is effective saturation, _r (m³ m^–3) is the residual volumetric water content, _s (m³ m^–3) is the saturated volumetric water content, K_s (cm d^–1) is the saturated hydraulic conductivity, and (cm^–1), n, and m (both dimensionless) are empirical parameters.

By superpositioning the unimodal VGM model, the bimodal function for water retention curves (Durner, 1994) can be obtained with

[16]

where w₁ and w₂ (0 < w₁, w₂ < 1; w_i = 1) are the weighting factors for the two overlapping regions. Combining Durner's (1994) retention model with Mualem's (1976) pore-size distribution model leads to (imnek et al., 2005)

[17]

Inverse parameter estimations were conducted with the procedures outlined by imnek et al. (1999). We included (i) the cumulative infiltration volumes I(t), (ii) the transient water content measured by the diagonally placed TDR probe _TDR(t), and (iii) the independently obtained (h) data points from laboratory steady-state measurements in the objective function. As an initial condition, we set the water content measured under the infiltration surface for the entire soil profile. We predicted the initial estimation of parameters from the measured soil texture and bulk density using the Rosetta database (Schaap et al., 2001).

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION THEORY MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Hood and Disc Infiltrometers
The hood infiltrometer consists of three components: a hood, a Mariotte water supply, and a U-tube manometer (Fig. 2 ). The first of the three major components is the hood itself (diameter = 12.4 cm), which is made of acrylic and is placed open side down onto the soil with a retaining ring. The gap between the retaining ring and the hood is filled with wetted sand to seal the edge and to prevent the water from leaking out of the side. The hood is connected to a conventional Mariotte water supply (diameter = 12 cm, length = 71.6 cm), which has the addition of a bubble tower placed inside its water reservoir. The bubble tower has an adjustable pipe that controls the suction in the usual way, by allowing air entry at varying distances below the water table of the tower. In contrast to the infiltration chamber of the conventional disk infiltrometer (e.g., Ankeny et al., 1991), an additional air outlet tube connects the head space of the water reservoir with the head space of the hood. The hood also contains a standpipe that is joined to the U-tube manometer. The purpose of this is to measure the effective pressure head on the soil surface, which we can determine with a precision of 1 mm from the difference of the height of the water level in the standpipe and the negative pressure head at the U-tube manometer. The zero point of the scale of the standpipe is at the soil surface level.

View larger version (20K): [in this window] [in a new window]   Fig. 2. Schematic of the hood infiltrometer (not to scale). The effective pressure head on the soil surface can be determined with a precision of 1 mm from the difference of the height of the water level in the standpipe and the negative pressure head at the U-tube manometer. The zero point of the scale of the standpipe is at the soil surface (US = negative pressure at the U-tube manometer, H = height of the water table in the standpipe, HK = infiltration chamber height, and T = submergence depth of the air pipe).

For those soils that have a tendency to surface seal, we recommend laying a nylon guard cloth on the soil under the hood to prevent soil surface sealing and fragmentation of soil aggregates during the time the hood is filling. The cloth will float in the water-filled hood and will not affect infiltration (see Fig. 3 ).

View larger version (20K): [in this window] [in a new window]   Fig. 3. Schematic of the hood with nylon guard cloth (not to scale).

The Site
Infiltration studies were conducted at the agrometeorological station of the Technical University of Berlin in Berlin-Dahlem. Vegetation at the study site is grassland. The soil is a Dahlem sandy loam (Cambisol) with a 25-cm-thick Ap horizon at the surface. Within this depth, the particle size distribution consists of 72.8% sand (0.063–2.0 mm), 19.2% silt (0.002–0.063 mm), and 8.0% clay (<0.002 mm). From soil core measurements, the bulk density within this depth was 1.403 (±0.035) g cm^–3.

Time-Domain Reflectometry Measurements
Before the infiltrometer measurements, we installed a 20-cm-long buriable three-rod TDR probe (Soil Moisture Equipment Corp., Santa Barbara, CA) to measure soil water content during all infiltration experiments. Similarly to the study by Schwartz and Evett (2003), we inserted the TDR probe at a 30° angle into the soil surface, 3 cm from the disk infiltrometer's edge, and oriented toward the vertical axis of the infiltrometer. The soil water content under the infiltration surface was automatically measured every 60 s. We used the polynomial function of Topp et al. (1980) to convert travel time into water content.

Hood and Disk Infiltrometer Measurements
Tap water was used for the infiltrometer measurements. We conducted three replicate sequences of hood infiltration experiments at the same place of the Dahlem soil site. We measured the infiltration rate at pressure supply heads of –5, –2, and 0 cm. Pressure heads below –5 cm were not possible because air entered into the hood through the soil. A differential pressure transducer was installed at the water reservoir to automatically record the infiltration rate every 30 s (Casey and Derby, 2002). We allowed 24 h between the end of each infiltration experiment and the beginning of the next.

Upon termination of the hood infiltration experiments, we performed three replicate sequences of disk infiltration experiments at the same place. For these experiments, we removed all vegetation from the infiltration surface and prepared a 10-mm-thick contact layer (K_s = 610 cm d^–1; air-entry pressure head = 32 cm) using dry spheriglass no. 2227 glass spheres (Potters Ballotini GmbH, Germany; Reynolds and Zebchuk, 1996). The particle diameter of these glass spheres was as follows: 87.3% 630–200 µm; 10.55% 200–63 µm, and 2.15% <63 µm. Then we wetted the contact material with a spray of water (Bagarello et al., 2000) and placed the prewetted disk onto its surface. We applied the following pressure supply heads: –15, –10, –5, and 0 cm H₂O. As before, the corresponding infiltration rates were registered every 30 s and the time interval between experiments was 24 h. A 10-mm-thick contact layer was necessary to level the marked microstructure of the soil surface.

Upon termination of the disk infiltrometer tests, we once more performed a hood infiltration experiment at the same place. For this experiment, the contact material was left on the infiltration surface. The purpose of this was to examine the influence of contact material on the infiltration rate. Three successive pressure steps were applied, corresponding with pressure heads of –5, –2, and 0 cm H₂O (Table 1). Table 1 shows that the initial water content under the infiltration surface was always similar in all experiments. Hence, we assumed that the 24-h waiting period between the measurements was sufficient for reestablishment of the original initial conditions.

	RESULTS AND DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION THEORY MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Wooding's Analysis
Hood Infiltrometer Measurements without Contact Layer
A summary of the hood infiltrometer results using Wooding's (1968) solution (Eq. [2]) is given in Table 2. Reproducible conductivities at any particular supply pressure head were obtained from the repeated hood infiltrometer measurements described in Table 2. The coefficients of variation between the calculated conductivities and their mean vary between 36 and 45%. Notice the relatively high saturated hydraulic conductivity of the first experiment compared with the corresponding values of the second and third hood infiltrometer experiments (Table 2). A decline in saturated hydraulic conductivity in successive infiltration experiments was also observed by Reynolds and Elrick (1986), Cislerova et al. (1988), and Bagarello et al. (2000). A reason for such a phenomenon may be that the steady-state infiltration was not always reached during the infiltration experiments. Under these conditions, Wooding's approach would overestimate the soil hydraulic conductivity (imnek et al., 1999). Inspection of the measured water contents below the hood (Fig. 4 ) shows that a stable water content was always reached at the end of any particular supply pressure head. The cause of the decline in saturated conductivity was that the saturated water content decreased throughout the hood experiments. We recorded the highest water contents, 0.389 m³ m^–3, under the hood during the first experiment (Table 1, Fig. 4), while in the sequencing infiltration experiments, the maximal water content was just 0.384 m³ m^–3.

View larger version (12K): [in this window] [in a new window]   Fig. 4. Measured water content below the hood during Exp. I. Arrows indicate step changes in the infiltrometer supply pressure head.

imnek et al., 1999

As shown in Table 2, the hydraulic conductivity decreased throughout our experiments. The values of the hood infiltrometer measurements without a contact layer were almost one order of magnitude greater than the corresponding values of the disk and hood experiments with a contact layer. The reasons for this are shown in Fig. 5 , which presents the relation between the final steady-state infiltration rate and the corresponding water content under the infiltration surface of all conducted infiltration tests. Figure 5 illustrates that while the water content rose only a little (<0.02 m³ m^–3), the final steady-state infiltration rate increased 10-fold. Our observed differences in maximal water content on the one hand and in saturated and near-saturated hydraulic conductivity on the other hand were caused not only by air entrapment and small modification of the soil structure during the infiltration experiments but also by the use of a contact material. As discussed above, Reynolds and Zebchuk (1996) showed that the hydraulic head loss across a contact layer can cause the pressure head applied to the soil surface to differ from the pressure head applied to the infiltrometer membrane. They developed a relationship to take into account the effect of the thickness of the contact layer on conductivity. The application of this equation to our disk measurements resulted in conductivity values that fell within 10% of the disk data listed in Table 2. Because of this, we conclude that the effect of the thickness of the contact layer on the conductivity is negligible compared with observed differences between the hood and disk infiltrometer results. We believe that preparing the soil surface for disk infiltrometer measurements led to the sealing and smearing of the pores of the soil surface, and applying pressure heads near saturation might have caused mobile fine-textured particles of the contact material to clog the macropores. The result was a significant decrease in the saturated and near-saturated conductivity compared with the measurements without a contact layer (Table 2). Our findings, a drop in saturated and near-saturated conductivity because of smeared pores, was also reported by Spohrer et al. (2006). We conclude that smearing, sealing, and clogging of pores lead to additional flow impedances in the soil surface layer. Because of that, saturated conditions underneath the disk will never be reached during the disk experiments. Further evidence of collapsed pores or pores filled with fine particles might be found by collecting vertical slices from the infiltration surface and examining them under a microscope; however, this was not done in this study.

View larger version (23K): [in this window] [in a new window]   Fig. 5. Final steady-state infiltration rate for an applied pressure head of h0 = 0 cm and the corresponding final water content under the infiltration surface for repeated infiltration experiments at the same place at the agrometeorological station of the Technical University of Berlin in Berlin-Dahlem (Germany). The time interval between the end of one infiltration run and the beginning of the next was at least 24 h.

Table 2 also shows the mean of the saturated conductivity of the soil cores obtained from the constant-head method. Compared with field measurements, the constant-head method yielded greater saturated conductivity (Table 2), possibly caused by the greater degree of saturation obtained during the laboratory procedure, leading to a greater number of water-filled pores. Another reason for the observed differences between the methods was discerned by Reynolds et al. (2000) when they compared the disk infiltrometer and the constant-head method for various soil textures and agricultural management practices. They found that often the constant-head method produced the highest conductivities regardless of soil type and land management. Reynolds et al. (2000) suggested that these higher conductivities may be attributed to worm holes, old root channels, and cracks. Such voids were never visible on both ends of the cores we investigated, however. Differences between the field and lab measurements might also be attributed to the different sample sizes of the infiltrometers and the soil cores.

Numerical Results
We also analyzed the measured disk data using the inverse parameter optimization method. The aim of the numerical studies was to test our thesis that soil surface alterations affected the disk infiltrometer measurements. Note that the inverse optimization of the parameters was not applied to the hood data. The reason for this is that hood infiltrometer experiments have a relatively small measurement range (from saturation up to the bubble point of the soil) and the applicable range in validity would be narrowed compared with the disk infiltrometer.

Optimization with Unimodal Functions
The results of the parameter estimation are listed in Table 3. Only small differences were found among the parameter values _r, _s, , K_s, and n of the repeated disk experiments. These values were located in a narrow range around the estimated mean (Table 3). The estimated parameters _s, , K_s, and n were only weakly correlated with each other (data not shown). In contrast, a relatively high correlation between the parameters _r and n (0.94–0.95) was found. Close agreement (generally <20 mL) was obtained between the measured and fitted cumulative infiltration curves of the second disk experiment (Fig. 6 ); larger deviations were mainly caused by step changes in the infiltrometer supply pressure heads. Similar results were obtained for the other disk experiments (data not shown). In spite of these good fits and the reasonable statistics (narrow 95% confidence interval and low degrees of parameter correlation), the predictions of water contents were poor (Fig. 7 , left side). The numerical model overestimated infiltration speed in the middle of the experiments and underestimated the water contents at the end; these deviations were up to 0.015 m³ m^–3.

View larger version (17K): [in this window] [in a new window]   Fig. 6. (a) Measured and calculated cumulative infiltration curves and (b) their differences for the disk infiltrometer, Exp. II. Arrows indicate step changes in the infiltrometer supply pressure head.

View larger version (27K): [in this window] [in a new window]   Fig. 7. Measured and calculated water content below the disk based on unimodal (van Genuchten, 1980) and bimodal (Durner, 1994) soil water retention functions. Arrows indicate step changes in the infiltrometer supply pressure head.

imnek et al., 1999

View larger version (26K): [in this window] [in a new window]   Fig. 8. Hydraulic conductivities of the Dahlem soil calculated using Wooding's (1968) solution and using numerical simulation (unimodal soil water retention function); h = supply pressure head.

Fohrer (1995) studied seal formation of a sandy loam soil (with similar texture and bulk density to the soil of our study) during laboratory rainfall experiments. She determined the saturated hydraulic conductivity of the seal layer to be between 1.2 and 3.6 cm d^–1, with our estimated values (geometric mean = 5.5 cm d^–1) being in this order (Table 3). Because of surface seal formation during the disk experiments, substantial discrepancies between the soil pressure head underneath the seal layer (at 0.5-cm depth) and the simulated pressure head applied on the soil surface existed in the numerical experiments (Table 4). The higher (less negative) the supply pressure head, the larger were the differences between the simulated soil pressure head at the 0.5-cm depth and the pressure head applied on the soil surface. Such discrepancies have also been reported by other researchers (e.g., Reynolds and Zebchuk, 1996; Wang et al., 1998). Our predicted soil pressure heads at the 0.5-cm depth indicate that saturated conditions were reached in none of our disk experiments. The additional flow impedance of the seal layer prevented the full range of available pore sizes from conducting. These simulation results are corroborated by our TDR measurements (Fig. 5) and also by Fohrer's (1995) results.

View larger version (21K): [in this window] [in a new window]   Fig. 9. (a) Unsaturated hydraulic conductivities at each supply pressure head (h) calculated using Wooding's analysis (the values were corrected as regards the soil pressure heads listed in Table 4) and the corresponding optimized hydraulic conductivity functions and (b) soil water retention values of the Dahlem soil from soil cores and optimized bimodal soil water retention curves obtained from three sequential disk infiltrometer experiments. The infiltration experiments were conducted at the same place: the agrometeorological station of the Technical University of Berlin in Berlin-Dahlem (Germany). Additionally, (a) shows unsaturated hydraulic conductivities of the Dahlem soil obtained from laboratory evaporation experiments. Laboratory soil water retention points were incorporated into the optimization processes.

	CONCLUSIONS

TOP NOTES ABSTRACT INTRODUCTION THEORY MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Disk infiltrometers are often used to determine the contribution of macropores to the infiltration rate and conductivity at saturation (Jury and Horton, 2004). Yet the presence of a contact layer in disk infiltrometer studies may lead to unrealistic conductivity values for pressure heads > –3 cm because of surface sealing, smearing, and clogging of pores. Steps or methods are required to circumvent these problems. For instance, Schwartz and Evett (2003) used a CaSO₄ solution to avoid sealing problems. We presented a new type of tension infiltrometer that, instead of requiring a disk and contact material, places a water-filled hood open side down onto the soil surface. The hood infiltrometer permits the measurement of the hydraulic conductivity including flow in macropores from field saturation up to the bubble point of the soil. The combined use of hood and disk infiltrometers in conjunction with TDR might be a powerful tool for the hydraulic characterization of field soils from saturation to dry conditions.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION THEORY MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
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Received for publication March 7, 2006.

	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION THEORY MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

• Ankeny, M.D., M. Ahmed, T.C. Kaspar, and R. Horton. 1991. Simple field method for determining unsaturated hydraulic conductivity. Soil Sci. Soc. Am. J. 55:467–469.[Web of Science]
• Assouline, S. 2004. Rainfall-induced soil surface sealing: A critical review of observations, conceptual models, and solutions. Vadose Zone J. 3:570–591.[Abstract/Free Full Text]
• Bagarello, V., M. Iovina, and G. Tusa. 2000. Factors affecting measurement of the near-saturated soil hydraulic conductivity. Soil Sci. Soc. Am. J. 64:1203–1210.[Abstract/Free Full Text]
• Bagarello, V., M. Iovino, and G. Tusa. 2001. Effect of contact material on tension infiltrometer measurements. Trans. ASAE 44:911–916.[Web of Science]
• Brooks, R.H., and A.T. Corey. 1964. Hydraulic properties of porous media. Hydrol. Pap. 3. Colorado State Univ., Fort Collins.
• Burdine, N.T. 1953. Relative permeability calculation from size distribution data. Trans. Am. Inst. Min. Metall. Eng. 198:71–78.
• Casey, F.X.M., and N.E. Derby. 2002. Improved design for an automated tension infiltrometer. Soil Sci. Soc. Am. J. 66:64–67.[Abstract/Free Full Text]
• Cislerova, M., J. imnek, and T. Vogel. 1988. Changes of steady-state infiltration rates in recurrent ponding infiltration experiments. J. Hydrol. 104:1–16.[CrossRef]
• Close, K.R., G. Frasier, G.H. Dunn, and J.C. Loftis. 1998. Tension infiltrometer contact interface evaluation by use of a potassium iodide tracer. Trans. ASAE 41:995–1004.[Web of Science]
• Dane, J.H., and J.W. Hopmans. 2002. Water retention and storage. p. 675. In J.H. Dane and G.C. Topp (ed.) Methods of soil analysis. Part 4: Physical methods. SSSA Book Ser. 5. SSSA, Madison, WI.
• Durner, W. 1994. Hydraulic conductivity estimation for soils with heterogeneous pore structure. Water Resour. Res. 30:211–223.[CrossRef]
• Everts, C.J., and R.S. Kanwar. 1993. Interpreting tension-infiltrometer data for quantifying soil macropores: Some practical considerations. Trans. ASAE 36:423–428.[Web of Science]
• Fohrer, N. 1995. Auswirkungen von Bodenfeuchte, Bodenart und Oberflächenbeschaffenheit auf Prozesse der Flächenerosion durch Wasser. (In German). Ph.D. diss. Technical Univ. of Berlin, Berlin, Germany.
• Gardner, W.R. 1958. Some steady-state solutions to the unsaturated flow equation with application to the evaporation from a water table. Soil Sci. 85:228–232.
• Jarvis, N.J., and I. Messing. 1995. Near-saturated conductivity in soils of contrasting texture measured by tension infiltrometers. Soil Sci. Soc. Am. J. 59:27–34.[Web of Science]
• Jury, W.A., and R. Horton. 2004. Soil physics. 6th ed. John Wiley & Sons, New York.
• Kung, K.-J.S., M. Hanke, C.S. Helling, E.J. Kladivko, T.J. Gish, T.S. Steenhuis, and D.B. Jaynes. 2005. Quantifying pore-size spectrum of macropore-type preferential pathways. Soil Sci. Soc. Am. J. 69:1196–1208.[Abstract/Free Full Text]
• Logsdon, S.D., and D.B. Jaynes. 1993. Methodology for determining hydraulic conductivity with tension infiltrometers. Soil Sci. Soc. Am. J. 57:1426–1431.[Web of Science]
• Logsdon, S.D., E.L. McCoy, R.R. Allmaras, and D.R. Linden. 1993. Macropore characterization by indirect methods. Soil Sci. 155:316–324.
• Mohanty, B.P., R.S. Bowman, J.M.H. Hendrickx, and M.Th. van Genuchten. 1997. New piecewise-continuous hydraulic functions for modeling preferential flow in an intermittent-flood-irrigated field. Water Resour. Res. 33:2049–2063.[CrossRef]
• Mualem, Y. 1976. A new model for predicting the hydraulic conductivity of unsaturated porous media. Water Resour. Res. 12:513–522.[CrossRef]
• Perroux, K.M., and I. White. 1988. Designs for disc permeameters. Soil Sci. Soc. Am. J. 52:1205–1215.[Abstract/Free Full Text]
• Renger, M., H. Stoffregen, J. Klocke, M. Facklam, G. Wessolek, C.H. Roth, and R. Plagge. 1999. Ein autoregressives Verfahren zur Bestimmung der gesättigten und ungesättigten hydraulischen Leitfähigkeit. (In German, with English abstract). J. Plant Nutr. Soil Sci. 162:123–130.
• Reynolds, W.D., B.T. Bowman, R.R. Brunke, C.F. Drury, and C.S. Tan. 2000. Comparison of tension infiltrometer, pressure infiltrometer, and soil core estimates of saturated hydraulic conductivity. Soil Sci. Soc. Am. J. 64:478–484.[Abstract/Free Full Text]
• Reynolds, W.D., and D.E. Elrick. 1986. A method for simultaneous in situ measurements in the vadose zone of field-saturated hydraulic conductivity, sorptivity and the conductivity–pressure head relationship. Ground Water Monit. Rev. 6(1):84–95.
• Reynolds, W.D., and D.E. Elrick. 1991. Determination of hydraulic conductivity using a tension infiltrometer. Soil Sci. Soc. Am. J. 55:633–639.[Web of Science]
• Reynolds, W.D., and W.D. Zebchuk. 1996. Use of contact material in tension infiltrometer measurements. Soil Technol. 9:141–159.[CrossRef]
• Schaap, M.G., F.J. Leij, and M.Th. van Genuchten. 2001. Rosetta: A computer program for estimating soil hydraulic parameters with hierarchical pedotransfer functions. J. Hydrol. 251:163–176.[CrossRef]
• Schwartz, R.C., and S.R. Evett. 2002. Estimating hydraulic properties of a fine-textured soil using a disc infiltrometer. Soil Sci. Soc. Am. J. 66:1409–1423.[Abstract/Free Full Text]
• Schwartz, R.C., and S.R. Evett. 2003. Conjunctive use of tension infiltrometry and time-domain reflectometry for inverse estimation of soil hydraulic properties. Vadose Zone J. 2:530–538.[Abstract/Free Full Text]
• Schwärzel, K., J. imnek, H. Stoffregen, G. Wessolek, and M.Th. van Genuchten. 2006. Direct and inverse estimation of the hydraulic properties of peat soils: Laboratory versus field data. Vadose Zone J. 5:628–640.[Abstract/Free Full Text]
• imnek, J., M. ejna, and M.Th. van Genuchten. 1998. The HYDRUS-2D software package for simulating the two-dimensional movement of water, heat and multiple solutes in variably saturated media, Version 2.0, IGWMC-TPS-53. Int. Ground Water Modeling Center, Colorado School of Mines, Golden.
• imnek, J., M. ejna, and M.Th. van Genuchten. 2005. The HYDRUS-1D software package for simulating the one-dimensional movement of water, heat and multiple solutes in variably saturated media. Version 3.0. HYDRUS Software Ser. 1. Dep. of Environ. Sci., Univ. of Calif., Riverside.
• imnek, J., O. Wendroth, and M.Th. van Genuchten. 1999. Estimating unsaturated soil hydraulic properties from laboratory tension disc infiltrometer. Water Resour. Res. 35:2965–2979.[CrossRef]
• Spohrer, K., L. Herrmann, J. Ingwersen, and K. Stahr. 2006. Applicability of uni- and bimodal retention functions for water flow modeling in a tropical Acrisol. Vadose Zone J. 5:48–58.[Web of Science]
• Topp, G.C., J.L. Davis, and A.P. Annan. 1980. Electromagnetic determination of soil water content: Measurement in coaxial transmission lines. Water Resour. Res. 16:574–582.[CrossRef]
• van Genuchten, M.Th. 1980. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Sci. Soc. Am. J. 44:892–898.[Web of Science]
• Vogel, T., and M. Cislerová. 1988. On the reliability of unsaturated hydraulic conductivity calculated from the moisture retention curve. Transp. Porous Media 3:1–15.[CrossRef]
• Wang, D., S.R. Yates, and F.F. Ernst. 1998. Determining soil hydraulic properties using tension infiltrometers, time domain reflectometry, and tensiometers. Soil Sci. Soc. Am. J. 62:318–325.[Abstract/Free Full Text]
• Warrick, A. 1992. Models for disc infiltrometers. Water Resour. Res. 28:1319–1327.[CrossRef]
• Wooding, R.A. 1968. Steady infiltration from a shallow circular pond. Water Resour. Res. 4:1259–1273.

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