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Pedosphere 18(4): 524532, 2008

ISSN 1002-0160/CN 32-1315/P

c 2008 Soil Science Society of China

Published by Elsevier Limited and Science Press

Boron and Zinc Transport Through Intact Columns ofCalcareous Soils

M. MAHMOOD-UL-HASSAN, M. S. AKHTAR and G. NABI

Institute of Natural Resources and Environmental Sciences, National Agricultural Research Center, Islamabad 45500(Pakistan). E-mail: [email protected]

(Received October 15, 2007; revised May 16, 2008)

ABSTRACT

Leaching of boron (B) and zinc (Zn) can be significant in some pedomorphic conditions, which can cause contaminationof shallow groundwater and economic losses. Boron and Zn adsorption and transport was studied using 8.4 cm diameter

28 cm long intact columns from two calcareous soil series with differing clay contents and vadose zone structures:

Lyallpur soil series, clay loam (fine-silty, mixed, hyperthermic Ustalfic Haplargid), and Sultanpur soil series, sandy loam

(coarse-silty, mixed, hyperthermic Ustollic Camborthid). The adsorption isotherms were developed by equilibrating soil

with 0.01 mol L1 CaCl2 aqueous solution containing varying amounts of B and Zn and were fitted to the Langmuir

equation. The B and Zn breakthrough curves were fitted to the two-domain convective-dispersive equation. At the end

of the leaching experiment, 0.11 L 10 g L1 blue dye solution was also applied to each column to mark the flow paths.

The Lyallpur soil columns had a slightly greater adsorption partition coefficient both for B and Zn than the Sultanpur

soil columns. In the Lyallpur soil columns, B arrival was immediate but the peak concentration ratio (the concentration

in solution at equilibrium/concentration applied) was lower than that in the Sultanpur soil columns. The breakthrough

of B in the Sultanpur soil columns occurred after about 10 cm of cumulative drainage in both the columns; the rise in

effluent concentration was fast and the peak concentration ratio was almost 1. Zinc leaching through the soil columns

was very limited as only one column from the Lyallpur soil series showed Zn breakthrough in the effluent where the peak

concentration ratio was only 0.05. This study demonstrates the effect of soil structure on B transport and has implications

for the nutrient management in field soils.

Key Words: adsorption isotherm, boron, intact soil column, transport parameters, zinc

Citation: Mahmood-ul-Hassan, M., Akhtar, M. S. and Nabi, G. 2008. Boron and zinc transport through intact columns

of calcareous soils. Pedosphere. 18(4): 524532.

INTRODUCTION

Boron in soil and water poses ecological and environmental problems and losses of agricultural

productivity in the soils where preferential flow is significant. Kang et al. (2002) ascribed B deficiency

in cabbage to leaching in humid areas. Surface-applied chemicals have been shown to travel rapidly

through small fractions of soil porosity (Radulovichet al

., 1992). Simulation models used for predictingwater and solute movement often fail to predict the arrival time accurately (Steenhuis et al., 1994;

Hatfield et al., 1997; Wildenschild et al., 1994; Vervoort et al., 1999).

The preferential flow pathways are only a small fraction of the total porosity causing a rapid and

accelerated breakthrough of both adsorbing and non-adsorbing solutes (Radulovich et al., 1992; Butcher

et al., 1995; Gupta et al., 1999). Accurate estimation of the solute velocities is essential for the prediction

of subsoil and groundwater contamination. Solute transport parameters can be predicted accurately

only after the breakthroughs over a range of flow rates are known.

Studies on B transport are limited in calcareous soils. Boron adsorption is considered to be reversible

but the use of models based on the assumption of local equilibrium often provides poor descriptions of B

transport in soil columns. Also, B transport is strongly related to soil pH (Communar and Keren, 2005).

It appears that soil pH and occurrence of macropores are two important characteristics controlling the


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BORON AND ZINC TRANSPORT THROUGH SOIL COLUMNS 525

leaching of B. Similarly, the leaching of Zn, which affects its fraction distribution in soils and availability

to plants, depends on the soil physical properties (Alvarez et al., 2001; Voegelin et al., 2003).

Adsorption coefficient (k) by batch technique helps to explain the results of leaching studies, and

given the pore water velocity, the leaching experiments can also yield k (Schweich et al., 1983; Bond and

Phillips, 1990a; Barnett et al., 2000). The batch experiment has the disadvantages of breakdown of soil

aggregates during sample agitation, the soil/solution ratio being relatively small, and the differences in

mass transfer and hydrodynamic conditions, which cumulatively result in inappropriate estimates of the

degree of adsorption (Schweich et al., 1983). The column technique, where the solution of the convection-

dispersion equation (CDE) helps to obtain k by fitting breakthrough curves (BTC), overcomes some of

these limitations but the disadvantage of the column technique is the absence of an accurate solution

for a nonlinear CDE with equilibrium adsorption (Veldhuizen et al., 1995). The disadvantage of column

study can be partly overcome by the application of semi-analytical solutions of a nonlinear transport

CDE (Bond and Phillips, 1990b).

Boron application is widely recommended for field crops (Rashid et al., 2002) but little information

is available on B adsorption and transport in calcareous soils. As part of a study on leaching of fertilizer

nutrients, objectives of this study were to determine whether the preferential flow of B and Zn actuallyoccurs in calcareous soils and to determine the transport parameters for these fertilizer nutrients.

MATERIALS AND METHODS

This study was carried out at the Institute of Natural Resources and Environmental Sciences, Na-

tional Agricultural Research Center, Islamabad, using intact columns of two calcareous soils, Lyallpur

and Sultanpur soil series (73 1073 45 E, 31 1031 30 N) from Bari Doab, an alluvial land-

mass between Ravi and Sutloj rivers with semi-arid subtropical continental climate (Mian, 1968). The

Lyallpur soil series (pH 8.2), clay loam (fine-silty, mixed, hyperthermic Ustalfic Haplargid) developed

on late Pleistocene, and Sultanpur soil series (pH 8.0), sandy loam (coarse-silty, mixed, hyperthermic

Ustollic Camborthid) developed on sub-recent level floodplain, are the most dominant soils in the region

used for maize-potato-maize cropping sequence. The saturated hydraulic conductivities, bulk densities,calculated mean pore volumes, and total porosities of the Sultanpur and Lyallpur soil series were 125

and 152 mm d1, 1.49 and 1.42 Mg m3, and 0.43 and 0.46 m3 m3, respectively.

The soil columns, 8.4 cm diameter and 28.0 cm long, were excavated by inserting PVC pipes, and

brought to laboratory. The bottom and surface of the columns were leveled by removing 1.5 cm soil

layer from each side. The bottom soil layer was supported by small gravels and plastic netting fixed on

a support PVC pipe of relatively large diameter resting on a ceramic funnel. The column was saturated

from the bottom by 0.01 mol L1 CaCl2 electrolyte solution.

For the leaching experiment, 10 mg L1 solution containing ZnSO4 and H3BO3 prepared in 0.01

mol L1 CaCl2 was applied on the column surface at a constant flow rate controlled by 2 cm water

head. The leachate was collected in plastic containers at time intervals and analyzed for B and Zn.

Boron and Zn adsorption coefficients were determined from adsorption isotherms developed throughbatch experiments (Syers et al., 1973; Castro and Rolston, 1977). The surface soil from each series was

passed through a 2-mm sieve and 5 g soil was equilibrated in triplicate with 30 mL 0.01 mol L1 CaCl2aqueous solution containing 0, 8, 20, 40, 80, 120, 160, 240, 320, 400, 480 mg B L 1 as H3BO3. The

suspension was shaken overnight on an end to end shaker at room temperature and then centrifuged.

The pH of the supernatant was recorded and B in the supernatant was analyzed. Separately, 5 g soil

in 30 mL of 0.01 mol L1 CaCl2 with 0, 25, 50, 100, 200, 300, 400, 500, 600, 700, and 800 mg Zn was

shaken overnight and the supernatant was analyzed for Zn. The amount of B or Zn added but not

recovered in solution was assumed to be adsorbed. Adsorption was expressed on a dry soil weight basis.

In addition to the leaching experiment, the flow paths were marked by applying brilliant blue dye

to the columns. 0.11 L 10 g L1 FD&C blue dye No. 1 solution was applied on the column surface

without causing runoff (Flury et al., 1994). After 24 hours, each column was cut perpendicularly with


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526 M. MAHMOOD-UL-HASSAN et al.

3 cm increments towards the center and the faces were photographed successively.

Boron was analyzed calorimetrically using the azomethine-H and the absorbance was recorded at 420

nm (Keren, 1996). Zinc was analyzed using an atomic absorption spectrophotometer. The adsorption

isotherms as determined from the batch experiment were fitted to the Langmuir equation (Castro and

Rolston, 1977), which has the form:

X=bKC

1 + KC(1)

or is rearranged in linear form:

C

X=

1

Kb+

C

b(2)

where X equals the adsorption by soil (mg kg1), C is the concentration in solution at equilibrium

(mg L1), K is a constant related to the binding strength (L mg1), and b is the maximum adsorption

on the soil (mg kg1). When C = 1/K, then X = b/2, or half of the sites on the soil are filled with

adsorbate.Boron and Zn adsorption isotherms were plotted as C/X versus C and regressed linearly. The

reciprocal of the slope of the regression line yielded b, the maximum B (or Zn) adsorption, and the

Langmuir constant K was obtained by dividing the slope by the intercept. To investigate the degree

of adsorption at the application concentration of 10 mg L1, we determined the adsorption partition

coefficient, k, by finding the tangent to the Langmuir isotherm at this concentration (Akhtar et al.,

2003). Differentiating Eq. 1 with respect to C gives:

X

C=

1

1 + KC+ bK

bK2C

(1 + KC)2(3)

or

k = 11 + KC

+ bK bK2

C(1 + KC)2

(4)

The CDE model for one-dimensional transport of reactive solutes subject to adsorption in one or

two domains has been solved for several boundary conditions given in Parker and van Genuchten (1984)

and other textbooks:

RC

t= D

2C

X2 v

C

X(5)

where R is the retardation factor for adsorbing solute, D is the dispersion coefficient, t is the time,

and v is the velocity of the solute and equals q/((k + ), where q is the water flux density, is the

mobile water fraction (Parker and van Genuchten, 1984), is the bulk density (Mg m3), and is the

total porosity (m3

m3

). To solve the differential equation, a constant adsorption partition coefficientis employed, resulting in solutions in which the movement of solutes can be scaled with a retardation

coefficient of the form (Toride et al., 1995):

R = 1 +k

(6)

All the breakthrough curves were fitted to CDE by partitioning into mobile/immobile fractions

using STANMOD, a Windows-based computer code, which uses analytical solutions of deterministic

non-equilibrium CDE (Simunek et al., 1999; Toride et al., 1995). The input data consisted of solute

concentration ratio C/C0, where C0 is the concentration applied, and drainage depth (cm) as proxy

for the solute concentration and time, respectively. The boundary conditions included a characteristic

length of 0.28 m and the total pulse input equaling to the drainage depth of the application phase. The


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R values calculated using Eq. 6 were used. No decay or production terms were included.

Furthermore, the uniqueness of the fitted parameters was verified by STANMOD run repeatedly for

each experiment with varying initial values of the input parameters (Langer et al., 1999). The fitted

parameters from the analytical solution were accepted once the goodness of fit (r2) was the highest and

the t value for the individual parameter was at least one (Kim et al., 2005). The mean square of error

for the model was < 0.01 in most cases. The fitted flow parameters for the breakthrough of B and Zn

were: Vm, the velocity in the mobile region defined as mv/ (cm h1), where m is the mobile water

fraction (m3 m3); Dm, the dispersion coefficient in the mobile region defined as mD/ (cm2 h1); ,

the mobile water partitioning coefficient (= m/); and , the mass transfer function (Simunek et al.,

1999; Toride et al., 1995).

RESULTS AND DISCUSSION

Flow path characteristics

The columns from both soils showed differences in flow paths as marked by the blue dye. Preferential

flow of blue dye was visible after uniform wetting of the surface 2 cm column depth but the nature offlow was different in each soil. In the Sultanpur soil series, a massive loam soil, blue dye after uniformly

wetting surface 2 cm soil flowed through 3 cm wide fingers and had no association with any pedological

feature (Fig. 1a, b), indicating existence of finger flow in this loamy soil. In the Lyallpur soil series,

the blue dye moved through macropores and then moved outward perpendicular to the flow paths,

suggesting diffusion into the matrix (Fig. 1c, d). The distribution of dyed area reflected differences

in the nature of flow paths in the soils: fingering and, possibly, macropore flow in the massive loam

Sultanpur soil series and only macropore flow in the Lyallpur soil series. Instability in the wetting

front causes finger flow and it occurs in homogenous soils (Wang et al., 2003), while macropore flow

is associated with biopores (earthworm burrows, decayed root channels, etc.) and the interpedal voids

and fissures form owing to shrinking and swelling (Beven and Germann, 1982).

Fig. 1 Patterns of blue dye staining in two columns from two soil series: Sultanpur, a sandy loam (a and b) and Lyallpur,a clay loam (c and d).


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Boron adsorption

Boron adsorption isotherms for both soils are depicted in Fig. 2a. Initially, there was a rapid increase

in B adsorption associated with the adsorption on the solid surface in both the soils. Then, it was followedby a slow rise of isotherm associated with the diffusion of B into the clay mineral. Boron adsorption

isotherm had a steeper slope for the Lyallpur compared to the Sultanpur soil series. Previously, Couch

and Grim (1968) proposed a two-step mechanism for B retention in soils. Griffin and Burau (1974) and

Sharma et al. (1989) observed a slow B desorption from clay soil and assumed that it could be due to

a slow B diffusion from the interior surfaces of clay mineral to the solution phase.

Fig. 2 Boron adsorption isotherms (mean of three replicates) for Lyallpur and Sultanpur soil series (a) and the Langmuirequation fit of the B adsorption isotherms for the Lyallpur (b) and Sultanpur (c) soil series. C is the concentration insolution at equilibrium and X is the adsorption by soil.

The B adsorption isotherms fitted the Langmuir equation (Eq. 2) well (Fig. 2b, c) (r2 = 0.75 in the

Lyallpur and 0.81 in the Sultanpur soil series). The maximum B adsorption and the binding strength

determined from the reciprocals of the slope and the intercept, respectively, of the regression line of

Langmuir equation were greater in Lyallpur compared with the Sultanpur soil series (Table I). Thisdifference appears to be related to the clay content as previously reported (Communar and Keren,

2005).

TABLE I

Langmuir adsorption parametersa) calculated from the linear B and Zn adsorption isotherms

Soil r2 Intercept Slope b K k R

mg kg1 L mg1

Boron Lyallpur 0.75 0.081 0.069 14.43 0.86 1.17 4.10

Sultanpur 0.81 0.102 0.070 14.25 0.69 1.10 3.90

Zinc Lyallpur 0.88 0.338 0.010 104 0.25 20.80 65.10

Sultanpur 0.85 0.044 0.010 94 0.23 18.00 63.37

a)r2 is the regression coefficient; intercept is 1/Kb; slope of the regression line between C/X vs. C is 1/b, where C isthe concentration in solution at equilibrium (mg L1) and X is the adsorption by soil (mg kg1); b is the maximumadsorption; K is a constant relating to the binding strength; k is the adsorption partition coefficient tangent to isotherm

at the concentration applied (10 mg L1); and R is the retardation coefficient.

Adsorption partition coefficients at C0 = 10 mg L1, the concentration applied during the leaching

experiment calculated with Eq. 4 using the fitted Langmuir parameters, are given in Table I. The

adsorption partition coefficient is assumed to be constant over the range of concentrations that occurred

in the soil. The surface soils had the adsorption partition coefficients in the range of 1.17 in the Lyallpur

and 1.1 in the Sultanpur soil series (Table I). Similarly, the retardation coefficient calculated from Eq. 6

was slightly greater in the Lyallpur as compared to the Sultanpur soil series (Table I). Therefore, the

Lyallpur soil series had slightly greater B adsorption potential than the Sultanpur series, which was


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related to their difference in clay content though they had very similar pH.

Zinc adsorption

Zinc adsorption isotherms for the soils are shown in Fig. 3a. Initially, there was a rapid increase in Znadsorption associated with the adsorption on the solids surface, which was then followed by a slow rise

of isotherm associated with diffusion into the clay mineral (Couch and Grim, 1968; Griffin and Burau,

1974; Sharma et al., 1989). Both soils had similar adsorption trend at low equilibrium concentration

( 1 mg L1), while at greater equilibrium concentrations, the Lyallpur soil series adsorbed relatively

greater Zn than the Sultanpur soil series. For example, the Lyallpur soil series adsorbed about 80 mg

kg1 and the Sultanpur soil series adsorbed approximately 70 mg kg1 at the equilibrium concentration

of 11 mg L1 and there was no further increase in adsorption with increase in equilibrium concentration

after 12 mg L1.

Fig. 3 Zinc adsorption isotherms (mean of three replicates) for the Lyallpur and Sultanpur soil series (a) and the Langmuirequation fit of the Zn adsorption isotherms for the Lyallpur (b) and Sultanpur (c) soil series. C is the concentration in

solution at equilibrium and X is the adsorption by soil.

The isotherms fitted to the Langmuir equation are depicted in Fig. 3b, c for both soils. The Langmuirequation fitted the data well (r2 = 0.88 in the Lyallpur and 0.85 in Sultanpur soil series). The Lyallpur

soil series had greater maximum Zn adsorption capacity (b) and binding strength (K) than the Sultanpur

soil series (Table I). The adsorption partition coefficient (k) calculated with Eq. 4 using the Langmuir

parameters (Table I) at C0 = 10 mg L1, which is the tangent to the slope at this concentration, was

21 in the Lyallpur and 18 in the Sultanpur soil series (Table I). Therefore, the Lyallpur soil series had

slightly greater Zn adsorption capacity than the Sultanpur soil series and it appeared that this may be

related to the clay content.

Boron breakthrough

Breakthrough curves plotted as a function of time, pore volumes of effluent, or cumulative drainage,

are a common tool to determine the transport properties (Jardine et al., 1988; Vereecken et al., 1990;Zurmhl, 1998). Boron breakthrough in Sultanpur soil columns occurred after 10 cm cumulative drainage

and the relative concentration (C/C0) peaked to 0.9 after 32 cm of cumulative drainage in Column 1

and to 1.0 after 40 cm of cumulative drainage in Column 2 (Fig. 4a). In both soils, the B breakthrough

occurred earlier than one pore volume. In the Lyallpur soil columns, the breakthrough was immediate

owing to high preferential flow; but after initially steep slope, C/C0 reached only 0.4 after 24 cm

of cumulative drainage in Column 1. Also, this curve shows a long tail (Fig. 4b), implying that the

concentration decrease was slow during the flushing phase. Diffusion of solutes perpendicular to the

flow path into matrix during the application phase and seeping back into the macropore during flushing

caused the long tail of BTC. The blue dye pattern in the soil also showed diffusion perpendicular to the

macropore (Fig. 1c, d). Although in Column 2 of the Lyallpur soil series the B breakthrough was also

immediate owing to high preferential flow, the C/C0 reached its peak of 0.1 after 13 cm of cumulative


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drainage (Fig. 4b). Therefore, we see delay in terms of concentration but not in terms of arrival time.

Fig. 4 Boron breakthrough curves in two columns from two soil series: Sultanpur, a sandy loam (a) and Lyallpur, a clayloam (b). C is the concentration in solution at equilibrium and C0 is the concentration applied.

In contrast, there was a relatively sharp decline in percolate B in the Sultanpur compared to the

Lyallpur soil columns during the flushing phase when B application was stopped and B-free water wasstarted. Macropore flow usually occurs near saturation; it does not depend on the water content of the

bulk matrix, but instead depends principally on the surface boundary conditions (Mahmood-ul-Hassan,

1998).

Zinc breakthrough

Breakthrough of Zn was very limited within the drainage depth in the two soil series. Only one

column from the Lyallpur soil series showed C/C0 of 0.05 toward the end of the leaching experiment

(data not presented). Transport parameters for Zn were not determined because of lack of breakthrough;

however, we had R values calculated from Eq. 6 using the k values from the batch experiment (Table I).

Model fitting

The two-domain CDE fitted well to the B breakthrough data except for one column of the Lyallpur

soil series, where r2 was only 0.44 (Table II). Boron under 20 mm water head moved 5.3 cm per cm of

drainage in the Sultanpur soil columns as determined by fitting the breakthrough curves. One column

of the Lyallpur soil series was as fast as the columns of the Sultanpur soil series but the other was

relatively slow. The water partitioning coefficient in the columns of the Sultanpur soil series was 0.97

compared to 0.30 and 0.07 for the two columns of the Lyallpur soil series. This indicated that larger

volume fraction of the Sultanpur soil series had taken part in the flow process, implying a lesser degree

of preferential flow compared to the Lyallpur soil series, which conformed to blue dye flow patterns,

i.e., finger flow in the Sultanpur and macropore flow in the Lyallpur soil series. However, the Lyallpur

soil columns had high dispersion in the mobile region (Table II). We believe that the high degree of

dispersion was probably due to rapid breakthrough of solutes owing to preferential flow paths.

TABLE II

Solute transport parametersa) determined using the convection-dispersion equation

Soil Column r2 w Vm Dm

cm h1 cm2 h1

Sultanpur 1 0.94 0.97 0.51 5.64 16.76

2 0.98 0.97 99.00 4.91 12.47

Lyallpur 1 0.88 0.30 0.87 5.28 42.45

2 0.44 0.07 79.44 2.23 458.66

a)r2 is the regression coefficient; is the water partitioning coefficient; is the mass transfer function; Vm is the velocityof the mobile liquid phase; and Dm is the dispersion coefficient of the mobile liquid phase.


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CONCLUSIONS

We investigated the leaching of B and Zn through two soils, the Sultanpur and Lyallpur soil series,

by taking replicated intact columns. We also marked the flow paths in the columns used and determinedB and Zn adsorption potential by batch experiment. This study provides a comparison of the observed

(from breakthrough curves) and calculated first arrival time (by fitting CDE solute transport model)

and shows that both soils had preferential flows that varied in nature and magnitude. The Lyallpur

soil, owing to its greater clay content, adsorbed greater B and Zn compared to the Sultanpur soil, but

its macropore flow had earlier breakthrough of B. However, the solute velocity in the columns of the

Lyallpur soil series was not higher than that of the Sultanpur soil series mainly because the solute

movement was attributed to high dispersion. The study demonstrates the effect of soil structure on

solute transport and has implications for the nutrient management in field soils.

REFERENCES

Akhtar, M. S., Richards, B. K., Medrano, P. A., deGroot, M. and Steenhuis, T. S. 2003. Dissolved phosphorus from

undisturbed soil cores: Related to adsorption strength, flow rate, or soil structure? Soil Sci. Soc. Am. J. 67:

458470.

Alvarez, J. M., Novillo, J., Obrador, A. and Lopez-Valdivia, L. M. 2001. Mobility and leachability of zinc in two soils

treated with six organic zinc complexes. J. Agr. and Food Chem. 49: 38333840.

Barnett, M. O., Jardine, P. M., Brooks, S. C. and Selim, H. M. 2000. Adsorption and transport of U(VI) in subsurface

media. Soil Sci. Soc. Am. J. 64: 908917.

Beven, K. and Germann, P. 1982. Macropores and water flow in soils. Water Resour. Res. 18: 13111325.

Bond, W. J. and Phillips, I. R. 1990a. Cation exchange isotherms obtained with batch and miscible-displacement tech-

niques. Soil Sci. Soc. Am. J. 54: 722728.

Bond, W. J. and Phillips, I. R. 1990b. Approximate solutions for cation transport during unsteady, unsaturated soil water

flow. Water Resour. Res. 26: 21952205.

Buchter, B., Hinz, C., Flury, M. and Fluhler, H. 1995. Heterogeneous flow and solute transport in an unsaturated stony

soil monolith. Soil Sci. Soc. Am. J. 59: 1421.

Castro, C. L. and Rolston, D. E. 1977. Organic phosphate transport and hydrolysis in soil: Theoretical and experimentalevaluation. Soil Sci. Soc. Am. J. 41: 10851092.

Communar, G. and Keren, R. 2005. Equilibrium and nonequilibrium transport of b oron in soil. Soil Sci. Soc. Am. J.

69: 311317.

Couch, E. L. and Grim, R. E. 1968. Boron fixation by illites. Clay Mineral. 16: 249256.

Flury, M., Fluhler, H., Jury, W. A. and Leuenberger, J. 1994. Susceptibility of soils to preferential flow of water: A field

study. Water Resour. Res. 30: 19451954.

Griffin, R. A. and Burau, R. G. 1974. Kinetic and equilibrium studies of boron desorption from soil. Soil Sci. Soc. Am.

J. 38: 892897.

Gupta, A., Destouni, G. and Jensen, M. B. 1999. Modelling tritium and phosphorous transport by preferential flow in

structured soil. J. Contam. Hydrol. 35: 389407.

Hatfield, K. K., Warner, G. S. and Guillard, K. 1997. Bromide and FD&C blue no 1 dye movement through intact and

packed soil columns. Trans. ASAE. 40: 309315.

Jardine, P. M., Wilson, G. V. and Luxmoore, R. J. 1988. Modeling the transport of inorganic ions through undisturbed

soil columns from two contrasting watersheds. Soil Sci. Soc. Am. J. 52: 12521259.

Kang, Y., Tsuji, M., Kosuga, H., Sakurai, K. and van Tran, K. 2002. Evaluating boron behavior in soil and water as a

step toward achieving sustainable agriculture. In IUSS (ed.) Proceedings of the 17th World Congress of Soil Science,

1421 August, 2002, Bangkok, Thailand. IUSS, Bangkok.

Keren, R. 1996. Boron. In Sparks, D. L. et al. (eds.) Methods of Soil Analysis. Part 3. Chemical and Microbiological

Properties. ASA and SSSA, Madison, WI. pp. 603626.

Kim, Y.-J., Darnault, C. J. G., Bailey, N. O., Parlange, J.-Y. and Steenhui, T. S. 2005. Equation for describing solute

transport in field soils with preferential flow paths. Soil Sci. Soc. Am. J. 69: 291300.

Langer, H. W., Gaber, H. M., Wraith, J. M., Huwe, B. and Inskeep, W. P. 1999. Preferential flow through intact soil

cores: Effect of matric head. Soil Sci. Soc. Am. J. 63: 15911598.

Mahmood-ul-Hassan, M. 1998. Water movement through unsaturated zone. Ph.D. Thesis, University of Reading, UK.

156pp.

Mian, M. A. 1968. Reconnaissance Soil Survey of Sahiwal District. Soil Survey of Pakistan, Lahore. 191pp.

Parker, J. C. and van Genuchten, M. T. 1984. Determining transport parameters from laboratory and field tracer

experiments. Va. Agr. Exp. Stat. B. 84(3): 193.


9/9


Radulovich, R., Sollin, P., Baveye, P. and Solorzano, E. 1992. Bypass water flow through unsaturated micro aggregated

tropical soils. Soil Sci. Soc. Am. J. 56: 721726.

Rashid, A., Rafiq, E. and Ryan, J. 2002. Establishment and management of boron deficiency in field crops in Pakistan.

In Goldbach, H. E. et al. (eds.) Boron in Plant and Animal Nutrition. Kluwer Academic/Plenum Publishers, New

York. pp. 339348.

Schweich, D., Sardin, M. and Gaudet, J. P. 1983. Measurement of a cation exchange isotherm from elution curves obtained

in a soil column: Preliminary results. Soil Sci. Soc. Am. J. 47: 3237.

Sharma, H. C., Pasricha, N. S. and Bajwa, M. S. 1989. Comparison of mathematical models to describe boron desorption

from salt affected soils. Soil Sci. 147: 7784.

Simunek, J., Van Genuchten, M. T., Sejna, M., Toride, N. and Leij, F. J. 1999. The STANMOD Computer Software

for Evaluating Solute Transport in Porous Media Using Analytical Solution of Convection-Dispersion Equation. U.S.

Salinity Laboratory Agri. Res. Service U.S. Dept. Agri., Riverside, California. 20pp.

Steenhuis, T. S., Boll, J., Shalit, G., Selker, J. S. and Merwin, I. A. 1994. A simple equation for predicting preferential

flow solute concentrations. J. Environ. Qual. 23: 10581064.

Syers, J. K., Browman, M. G., Smillie, G. W. and Corey, R. B. 1973. Phosphate sorption by soils evaluated by the

Langmuir adsorption equation. Soil Sci. Soc. Am. J. 37: 358363.

Toride, N., Leij, F. J. and van Genuchten, M. T. 1995. The CXTFIT Code for Estimating Transport Parameters from

Laboratory or Field Tracers Experiments. Version 2.1. Research Report No. 137. U.S. Salinity Laboratory Agri.

Res. Service U.S. Dept. Agri., Riverside, California. 121pp.

Veldhuizen, M., Appelo, C. A. J. and Griffioen J. 1995. The (least squares) quotient algorithm as a rapid tool for obtainingisotherm form from column elution curves. Water Resour. Res. 31: 849857.

Vereecken, H., Maes, J. and Feyen, J. 1990. Estimating unsaturated hydraulic conductivity from easily measured soil

properties. Soil Sci. 149: 112.

Vervoort, R., Radcliffe, W. D. E. and West, L. T. 1999. Soil structure development and preferential solute flow. Water

Resour. Res. 35: 913928.

Voegelin, A., Barmettler, K. and Kretzschmar, R. 2003. Heavy metal release from contaminated soils. Soil Sci. Soc. Am.

J. 32: 865875.

Wang, Z., Tuli, A. and Jury, W. A. 2003. Unstable flow during redistribution in homogeneous soil. Vadose Zone J. 2:

5260.

Wildenschild, D., Jensen, K. H., Villholth, K. and Illangasekare, T. H. 1994. A laboratory analysis of the effect of

macropores on solute transport. Ground Water. 32: 381389.

Zurmhl, T. 1998. Capability of convection-dispersion transport models to predict transient water and solute movement in

undisturbed columns. J. Contam. Hydrol. 30: 101128.

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