This article was downloaded by: [UQ Library]On: 05 November 2014, At: 12:29Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number:1072954 Registered office: Mortimer House, 37-41 Mortimer Street,London W1T 3JH, UK

Communications in SoilScience and Plant AnalysisPublication details, including instructions forauthors and subscription information:http://www.tandfonline.com/loi/lcss20

Kinetics of potassiumdesorption by Alfisols ofGreeceA. Ioannou a b , A. Dimirkou a , M. Doula a &Ch. Paschalidis aa Department of Chemistry , University ofAthens , Panepistimiopolis‐Zografou, Athens,15771, Greeceb 14 Thermopillon Street, Pallini, 15344,GreecePublished online: 11 Nov 2008.

To cite this article: A. Ioannou , A. Dimirkou , M. Doula & Ch.Paschalidis (1994) Kinetics of potassium desorption by Alfisols of Greece,Communications in Soil Science and Plant Analysis, 25:9-10, 1355-1372, DOI:10.1080/00103629409369120

To link to this article: http://dx.doi.org/10.1080/00103629409369120

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of allthe information (the “Content”) contained in the publications on ourplatform. However, Taylor & Francis, our agents, and our licensorsmake no representations or warranties whatsoever as to the accuracy,completeness, or suitability for any purpose of the Content. Anyopinions and views expressed in this publication are the opinions andviews of the authors, and are not the views of or endorsed by Taylor& Francis. The accuracy of the Content should not be relied upon andshould be independently verified with primary sources of information.

Taylor and Francis shall not be liable for any losses, actions, claims,proceedings, demands, costs, expenses, damages, and other liabilitieswhatsoever or howsoever caused arising directly or indirectly inconnection with, in relation to or arising out of the use of the Content.

This article may be used for research, teaching, and private studypurposes. Any substantial or systematic reproduction, redistribution,reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms & Conditions of accessand use can be found at http://www.tandfonline.com/page/terms-and-conditions

Dow

nloa

ded

by [

UQ

Lib

rary

] at

12:

29 0

5 N

ovem

ber

2014

COMMUN. SOIL SCI. PLANT ANAL., 25(9&10), 1355-1372 (1994)

KINETICS OF POTASSIUM DESORPTION BY ALFISOLS OF GREECE

A. Ioannou,1 A. Dimirkou,2 M. Doula2 and Ch. Paschalidis2

University of Athens, Department of Chemistry, Panepistimiopolis-Zografou Athens15771, Greece

ABSTRACT: Kinetics of K desorption was studied on Alfisol Haploxeralf

samples of central Greece. Calcium-saturated samples were equilibrated with

different potassium concentrations and pH for 96 hours at pH 5.0, 6.0, 7.0 and 8.0

and initial potassium concentrations of 7, 35, 54 and 112 ppm. Samples were

continuously leached with 0.01 M CaCL2 until K was not detected in the leachate.

Desorption was nearly complete in approximately 3 to 4 hours for the Alfisol

Haploxeralf. When the initial K concentrations varied between 0-7, 7-35, 35-54

and 54-112 ppm, then approximately 95-97%, 93-98%, 75-96% and 18-75%,

respectively, was subsequently desorbed from Alfisol Haploxeralf samples. Three

mathematical models (first order, power function and parabolic diffusion) were

used to describe cumulative potassium release at different values of pH and

initially adsorbed K. Comparisons of coefficients of determination (r2) indicated

that the first order, power function and parabolic diffusion equations adequately

described cumulative potassium release for all studied pH and initially adsorbed

potassium. Apparent potassium desorption rate coefficients (k) ranged from 4.3 x

10-3 to 11.43 × 10-3 min-1. The magnitude of the k values decreased as adsorbed

1 Postal address of the corresponding author: A. Ioannou, 14 Thermopillon Street,Pallini, 15344, Greece.

2 National Agricultural Research Foundation, Soil Science Institute of Athens, 1 S.Venizelou Street, Lycovrissi, 141 23, Greece.

1355

Copyright © 1994 by Marcel Dekker, Inc.

Dow

nloa

ded

by [

UQ

Lib

rary

] at

12:

29 0

5 N

ovem

ber

2014

1356 IOANNOU ET AL.

potassium and pH increased. Finally all the studied models were transformed to

pH-dependent forms.

INTRODUCTION

Equilibrium reactions existing between solution and exchangeable phases

of soil K profoundly influence K chemistry. The rate and direction of these

reactions determine whether applied K will be leached into lower soil horizons,

absorbed by plants, converted into unavailable forms or released into available

forms. Little has appeared in the literature concerning the kinetics of K desorption

in soil systems at different values of adsorbed potassium and pH. A knowledge

of the reaction rates between solution and exchangeable phases of soil K at pH

5.0, 6.0, 7.0 and 8.0 is necessary in order to predict the fate of added K fertilizer

in soils and to properly make K fertilizer recommendations.

Soil K desorption has been described by several equations. Simple first-

order equations were used by Jardine and Sparks (1984), Munn et al. (1976),

Ogwada and Sparks et al. (1985), Sparks and Jardine (1981) and Sparks et al.

(1980) to describe K desorption over short time periods (< 1000 h) from several

soils, while Talibudeen et al. (1978) used three simultaneous rate terms. In

contrast, Feigenbaum et al. (1981) described K desorption kinetics from three

micas (biotite, muscovite and phlogopite) by a parabolic diffusion rate equation.

The modified Elovich and power-form equations have also been used to describe

K desorption from soils (Havlin et al., 1985; Martin and Sparks, 1983), although

their applications have been limited to long time periods (> 1000 h) and

nonexchangeable K release.

Feigenbaum and Levy (1977) studied K release in 0.01 M CaCl2 and

deionized H2O extracts from two soils with relatively high K contents. The amount

of release was greater from the soil having a high portion of total K in the silt

fraction. Talibudeen et al. (1978) observed that the rate of release of soil K was

linearly proportional to time172. They assumed uniform distribution of K in

spherical particles and developed planar diffusion models for K release from the

surface and from peripheral layers in these calculations. Surface K ceased to

contribute to K release after 24 hours and peripheral K after 840 hours

(Talibudeen and Day, 1968). Arnold (1959) used saturated resins containing either

Ca or Na concentrations-in excess of exchangeable soil K to investigate desorption

Dow

nloa

ded

by [

UQ

Lib

rary

] at

12:

29 0

5 N

ovem

ber

2014

KINETICS OF K DESORPTION 1357

Table I. Soil taxonomic classification and particle size distribution of the soil.

Taxonomic

classification

Alfisol

Haploxeralf

Depth

cm

0-50

Sand

%

16

Silt

%

14

Clay

%

70

of K. Equilibrium of K exchange between the soil and the resin was attained in

about 96 hours. Selim et al. (1976) proposed that a kinetic reaction existed

between soil solution and exchangeable K with a first order desorption rate

coefficient (kd).

Sparks et al. (1980) studied the kinetics of K adsorption from solution to

exchangeable phases for two Dothan soils. Equilibrium of K exchange was

reached in 2 hours with the 5 and 25 ng/ml K solution and in about 24 hours with

the 100 ng/ml K solution. This slow rate of K exchange was attributed to

diffusion-controlled exchange in these soils with vermiculitic mineralogy. The

adsorption rate coefficients ranged from about 0.7 to 22.0 hours"1 and generally

decreased at higher initial concentrations of solution K. The objectives of this

study were to determine the time, pH and initial concentration dependencies of

potassium desorption by Alfisols Haploxeralf samples. To this end we measured

the potassium desorption capacity and the apparent reaction rate coefficients of

desorption using an initial K concentration range of 7 to 112 ppm and a solution

pH range of 5.0, 6.0, 7.0 and 8.0. Kinetic results were compared using the first

order, Elovich and parabolic diffusion models.

MATERIALS AND METHODS

Soils Studied: Studies were performed on soil located in central Greece. The

taxonomic classification is given in Table I. Physical and chemical properties of

the studied soil are given in Table II. The sample was air-dried and crushed to

pass a 2-mm sieve. Particle size analysis was determined by the pipette method

(Kilmer and Alexander, 1949). Organic matter was determined by the Walkley-

Black (1934) method, and cation exchange capacity by a MgCl2 saturation with

Dow

nloa

ded

by [

UQ

Lib

rary

] at

12:

29 0

5 N

ovem

ber

2014

1358 IOANNOU ET AL.

Table II. Physical and chemical properties of soil.

Sample

Alfisol

Haploxeralf

Liquid

Limit

68

EC

mmhos/cm

<3

pH

1:2

7.8

C.E.C

meq/100g

42

CaCO3

eouiv.

%

2.6

Organic

matter

%

0.8

Exchangeable

K meq/lOOg

0.80

after Ca-

sa tura tion

treatment

CE.C

48.25

after

Ca-saturatíon

treatment

pH

7.1

subsequent displacement by CaCl2 (Okazaki et al., 1963; Rich, 1962). The

exchangeable K was determined following extraction by 1 N ammonium acetate,

pH 7. The electrical conductivity (E.C.) was measured in a saturated paste of the

soil. The pH measurements were obtained from a 1:2 soil/water mixture. The

CaCO3 equivalent was determined by treatment with dilute acid and the volume

of released CO2 measured by the Bernard calcimeter.

Sample Preparation: Prior to initiation of the kinetic desorption studies,

subsamples from the soil were Ca-saturated using 1 N CaCl2. The soil was

subsequently washed with deionized water, followed by 1:1 acetone-H20 mixture

until a negative test for Cl" was obtained with AgNO3. The soil was saturated with

Ca; as in most mineral soils, this is one of the predominant cations. Also, by first

saturating with this cation, most exchangeable K was removed from the soils. The

saturated sample was air-dried and crushed to pass a 2-mm sieve. Soil pH was

measured on Ca-saturated samples using 1:2 soil/water mixtures. The C.E.C. of

Ca-saturated samples was ascertained by displacement with 1 N MgCl2. The

quantity of Ca in solution was measured using atomic absorption spectro-

photometry.

Dow

nloa

ded

by [

UQ

Lib

rary

] at

12:

29 0

5 N

ovem

ber

2014

KINETICS OF K DESORPTION 1359

Kinetics of Desorption Studies: Desorption studies were carried out using

triplicate 1-g Ca-saturated samples, which were placed in 100-ml polypropylene

centrifuge tubes with 30-ml of 11, 58, 90 and 195 ug K/ml solution and 20 ml of

buffer solution at pH levels of 5.0, 6.0, 7.0 and 8.0. The suspension was shaken

for 19 hours at 25°C on a reciprocating shaker. At the end of the equilibration

period, the 50-ml suspension was filtered and all the filtered aliquot was collected

for the determination of the quantity of K on exchange sites at zero time of

desorption. Afterwards the sample on the filter paper was leached with 0.01 M

CaCl2. The CaCl2 was passed through the soil and the milliliter aliquots were

collected every 15 min. until K was not detected in the leachate for the

determination of K on soil exchange sites at time t of desorption. Potassium in the

leachate was determined by flame photometer.

Three mathematical models were used to describe the kinetics of K

desorption by Alfisol Haploxeralf samples.

1. The first order equation described by Havlin et al. (1985):

log — = log a - kt (la)Xo

If A = loga and k = B, then

log *L = A - Bt (lb)Xo

where Xt = quantity of K on soil exchange sites at time t of desorption, Xo =

quantity of K on exchange sites at zero time of desorption, t = time in minutes

and k = desorption rate coefficient in min'1, k is determined by the slope of log

(Xt/Xo) vs. t (Figures 1 and 2). A was determined by the intersection of the plot

log (Xt/Xo) versus t. The pH-dependent equations of desorption rate coefficient

(k) were derived from the plots of k vs. pH for each initial K concentration (Table

IV).

2. The power function equation as described by Havlin et al. (1985)

inX = a + b Int (2)

In equation 2, X is the amount of K desorbed (ug K/g soil) at time t, a and b

Dow

nloa

ded

by [

UQ

Lib

rary

] at

12:

29 0

5 N

ovem

ber

2014

1360 IOANNOU ET AL.

v •

-0,5-

-1 -

-2 •

Co =

^ ^

1 ; 1— 1 1—; 1-

7 ppm

1 —1 1—

• pHSOpH6ApH7OpH8

" ^ O

—1 1

20 40 60 80 100 120

Time .minutes

140 160 180 200

Figure 1. Log (Xt/Xo) vs. time of leaching with 0.01 M CaCl2 from AlfisolHaploxeralf for pH 5.0, 6.0, 7.0, 8.0 and initial K concentration of 7 ppm.

50 100

Time .minutes

150 200

Figure 2. Log (Xt/Xo) vs. time of leaching with 0.01 M CaCl2 from AlfisolHaploxeralf for pH 5.0, 6.0, 7.0, 8.0 and initial K concentration of 112 ppm.

Dow

nloa

ded

by [

UQ

Lib

rary

] at

12:

29 0

5 N

ovem

ber

2014

KINETICS OF K DESORPTION 1361

constants. The values of a and b were determined by the slopes and intercepts of

the plot InX vs. Int for studied amount of K adsorbed and pH. The square of

linearity coefficient (r2) was used for comparison of the goodness of fit.

3. The parabolic diffusion kinetic model in the following form:

%X = a + Ulß (3)

In this equation, %X is the percent of potassium desorbed at time t, a and b

constants. The values of a and b were determined by the slopes and intercepts of

the plot %X versus tm.

RESULTS AND DISCUSSION

Potassium desorption in the studied soil conformed to first-order kinetics

(Figures 1 and 2). The first-order rate equation described K desorption for an

average of 180 min. for Alfisol Haploxeralf Ca-saturated samples. The first-order

rate equation described K desorption well (r2 = 0.993)(Table III). The finding that

the kinetics of K desorption is first-order supports the proposal by Selim et al.

(1976). The A, B or k, r2 values for every studied initial concentration and pH are

given in Table III.

The desorption rate coefficient values (k) ranged from 4.3 x 10'3 to 11.4

x 10'3 min.'1 for Alfisol Haploxeralf. Since the plots of B or k constants versus pH

for studied concentrations gave r2 > 0.997, the pH-dependent form of B or k is

represented in Table VI.

The kinetics of K desorption was 2-3 hours slower than the kinetics of K

absorption. This would be expected due to the difficulty in desorbing K from

partially collapsed interlayer positions (Sawhney, 1966). Once K is adsorbed into

the interlayer positions, the coulombic attraction between K ions and the clay

layers would be greater than the hydration forces of the ions, resulting in partial

layer collapse (Sawhney, 1966). The observation of slower desorption than

adsorption conforms with the finding of others (Kuo and Lotse, 1973) and

suggests that the K kinetic reactions in Alfisols Haploxeralf were nonsigural or

that hysterisis could be occurring (Ardakani and McLaren, 1977; Rao and

Davidson, 1978).

Potassium desorption as plotted by the power function equation (Havlin et

al., 1985) for all studied pH and initial potassium concentrations (Figures 3 and

Dow

nloa

ded

by [

UQ

Lib

rary

] at

12:

29 0

5 N

ovem

ber

2014

1362 IOANNOU ET AL.

Table III. Intercept and slope values (A, B) of the first-order kinetic model andcorrelation coefficient (r2) at different, pH, initial concentration andadsorbed K.

Co

ppm

7

35

54

112

72

pH

5.0

6.0

7.0

8.0

5.0

6.0

7.0

8.0

5.0

6.0

7.0

8.0

5.0

6.0

7.0

8.0

C*

pgK/g

122

160

198

236

871

957

1043

1129

1264

1371

1478

1585

2607

2821

3035

3249

A

-0.106

-0.106

-0.105

-0.105

-0.096

-0.085

-0.083

-0.760

-0.082

-0.079

-0.079

-0.840

-0.077

-0.064

-0.045

-0.059

k o r B

11.4x10-3

9.0xl0-3

8.0x10-3

6.6xlO-3

10.3x10-3

8.9x10-3

7.5x10-3

6.1xlO-3

9.8x10-3

8.6x10-3

7.1x10-3

5.6xlO-3

7.8x10-3

6.8x10-3

5.7x10-3

4.3x10-3

r2

0.998

0.998

0.998

0.988

0.999

0.999

0.999

0.998

0.999

0.999

0.999

0.999

0.998

0.997

0.996

0.997

0.998

C* : adsorbed potassium pgK/g soil at t=0

Dow

nloa

ded

by [

UQ

Lib

rary

] at

12:

29 0

5 N

ovem

ber

2014

KINETICS OF K DESORPTION 1363

Table IV. Intercept and slope values (a, b) of the power function model andcorrelation coefficient (r2) at different, ph, initial concentration andadsorbed K.

Co

ppm

7

35

54

112

r2

pH

5.0

6.0

7.0

8.0

5.0

6.0

7.0

8.0

5.0

6.0

7.0

8.0

5.0

6.0

7.0

8.0

C*

pgK/g

122

160

198

236

871

957

1043

1129

1264

1371

1478

1585

2607

2821

3035

3249

a

3.62

3.61

3.61

3.59

5.38

5.28

5.16

4.95

5.68

5.54

5.35

5.21

6.01

5.79

5.56

5.58

b

0.240

0.280

0.320

0.360

0.280

0.310

0.350

0.390

0.287

0.328

0.377

0.407

0.362

0.415

0.465

0.496

r2

0.932

0.953

0.977

0.983

0.953

0.965

0.983

0.996

0.958

0.966

0.971

0.991

0.967

0.973

0.986

0.995

0.972

C* : adsorbed potassium ugK/g soi! at t=0

Dow

nloa

ded

by [

UQ

Lib

rary

] at

12:

29 0

5 N

ovem

ber

2014

1364 IOANNOU ET AL.

Table V. Intercept and slope values (a, b) of the parabolic diffusion model andcorrelation coefficient (r2) at different, ph, initial concentration andadsorbed K.

Co

ppm

7

35

54

112

r2

pH

5.0

6.0

7.0

8.0

5.0

6.0

7.0

8.0

5.0

6.0

7.0

8.0

5.0

6.0

7.0

8.0

C*

pgK/g

122

160

198

236

871

957

1043

1129

1264

1371

1478

1585

2607

2821

3035

3249

a

48.034

39.700

31.292

22.886

40.500

32.729

24.900

16.300

37.423

29.260

21.350

14.115

24.472

15.455

7.290

1.973

b

4.135

4.780

5.280

5.675

4.740

5.232

5.600

6.000

4.939

5.470

5.861

6.063

5.753

6.263

6.545

6.405

T2

0.845

0.904

0.938

0.963

0.897

0.928

0.960

0.979

0.917

0.937

0.962

0.981

0.943

0.956

0.979

0.991

0.943

C* : adsorbed potassium pgK/g soil at t=0

Dow

nloa

ded

by [

UQ

Lib

rary

] at

12:

29 0

5 N

ovem

ber

2014

KINETICS OF K DESORPTION 1365

Table VI. The equations of k of the first-order rate model as a function of pHfor each initial K concentration and r2 values.

Co

ppm K

7

35

54

117

k = f(pH)

0.0195-0.0016pH

0.0173-0.0014pH

0.0169-0.0014pH

0.0137-0.0012pH

T2

0.998

0.999

0.997

0.994

6 y

5 • •

4 • •

3 • •

2 • •

1 • •

O •-

Co = 7 ppm

• pH 5OpH 6ApH7OpH 8

3

kit

Figure 3. Power function kinetics for potassium desorption at 25°C using 0.01M CaCl2 from Alfisol Haploxeralf as a function of lnt at ph 5.0, 6.0, 7.0, 8.0 andinitial K concentration of 7 ppm.

Dow

nloa

ded

by [

UQ

Lib

rary

] at

12:

29 0

5 N

ovem

ber

2014

1366

8,1 • •

7,9-

7 , 7 • •

Iß ••

7,1 • •

6,9 -

IOANNOU ET AL.

Co = 112 ppm

3.5

• pH 5OpH7

4,5 5,5

Int

Figure 4a. Power function kinetics for potassium desorption at 25°C using 0.01M CaCl2 from Alfisol Haploxeralf as a function of lnt at ph 5.0 and 7.0 and initialK concentration of 112 ppm.

4) showed that desorbed K. increased as initial K concentrations and pH increased.

The a, b and r2 values for every studied initial K concentration and pH are given

in Table IV. The linearity of the plots InX vs. lnt (Figures 3 and 4) and r2 = 0.972

proved that potassium desorption conformed to the power function equation. Since

the plots of a and b versus pH for studied initial concentrations gave r2 > 0.957,

the pH-dependent forms of a and b are represented in Table VII.

That diffusion was the predominant mechanism of K desorption in this soil

for all studied initial K concentrations and pH is illustrated in Figures 5 and 6.

The r2 values for the comparison of goodness to fit and a and b constants of the

equations of the percent of K desorbed as a function of square root of time are

given in Table VI. These data agree with Barshad (1954), who ascribed a linear

relationship between time"2 vs. % K desorption to diffusion-controlled exchange.

There was some deviation in linearity of the diffusion plots during the initial

period of K desorption and low adsorbed K for soils (Figures 5 and 6). Chute and

Quirk (1967) note that diffusion-controlled exchange may not be strictly obeyed

Dow

nloa

ded

by [

UQ

Lib

rary

] at

12:

29 0

5 N

ovem

ber

2014

KINETICS OF K DESORPTION 1367

8,1 j

7,9 -•

7,7 •

7.5 . -

73 ••

7,1

6.9

Co = 112 ppm

O

3,5 4,5

Int

• pH 6OPH8

5,5

Figure 4b. Power function kinetics for potassium desorption at 25°C using 0.01M CaCl2 from Alfisol Haploxeralf as a function of lnt at ph 6.0 and 8.0 and initialK concentration of 112 ppm.

Table VII. The equations of a and b of the power function model as a functionof pH for each initial K concentration and r2 values.

Co

ppm K

7

35

54

117

7

35

54

117

~ 2

a

3.666-0.009pH

6.109-0.141pH

6.496-0.162pH

6.708-0.149pH

b

0.040+0.040pH

0.092+0.037pH

0.084+0.041pH

0.141+0.045pH

r2

0.853

0.968

0.997

0.864

r2

0.999

0.996

0.992

0.987

0.957

Dow

nloa

ded

by [

UQ

Lib

rary

] at

12:

29 0

5 N

ovem

ber

2014

1368 IOANNOU ET AL.

100 i

90 •8 0 •

7 0 •

6 0 •

SO •

4 0 •

30 •

2 0 •

1 0 •

Co = 7 ppm

0 2 4

0•A

V6

Time

S•A

8

, minutes

A

10

Î I \

• pHSOpH6

APHB

12 1

Figure 5. Percent K desorption vs. time"2 for Alfisol Haploxeralf at pH 5.0, 6.0,7.0, 8.0 and initial K concentration of 7 ppm.

100 i90 •

80 -

70 •

60 •

50 •

40 -30 •

20 -10 •

(

Co = 112

) 2 4

ppm

•O•A

6

VTime,

O•A

8

minutes

O A

A A

A

10

6 2A AA

• pH5OpH6ApH7

12 1

Figure 6. Percent K desorption vs. time"2 for Alfisol Haploxeralf at pH 5.0, 6.0,7.0, 8.0 and initial K concentration of 112 ppm.

Dow

nloa

ded

by [

UQ

Lib

rary

] at

12:

29 0

5 N

ovem

ber

2014

KINETICS OF K DESORPTION 1369

Table VIH. The equations of a and b of the parabolic diffusion model as afunction of pH for each initial K concentration and r2 values.

Co

ppm K

7

35

54

117

7

35

54

117

T2

a

89.982-8.385pH

80.886-8.043pH

76.129-7.783pH

61.478-7.566pH

b

1.640+0.512pH

2.697+0.415pH

3.137+0.376pH

4.787+0.224pH

r2

0.999

0.999

0.999

0.988

r2

0.988

0.996

0.963

0.700

0.954

during the initial period of K desorption. This could be due to mass action

exchange at sites on external surfaces and by (Helfferich, 1962) the initial

curvilinear relationship due to release of K from the external planer surface sites,

suggesting that film diffusion was the rate-controlling process. In our study the

percent of K desorption increases by increasing pH but decreases by increasing

adsorbed K. Since the plots a and b versus pH for studied initial concentration and

pH gave r2 > 0.954, the pH-dependent forms of a and b are represented at Table

VIII.

CONCLUSIONS

The general conclusions of this study were:

L All the studied models described potassium desorption as evidenced by the

high linearity coefficients.

Dow

nloa

ded

by [

UQ

Lib

rary

] at

12:

29 0

5 N

ovem

ber

2014

1370 IOANNOU ET AL.

2. The desorption rate coefficient of the first-order rate equation decreases by

increasing initial K concentration and pH.

3. The desorbed K increase by increasing initial potassium concentration and

pH.

4. The percent of K desorption decreases by increasing pH values.

5. The percent of K desorption decreases by increasing initial K concentration.

6. All the studied models could be transformed to pH-dependent forms since

all the pH dependent forms of constants k, a and b have high r2 values.

REFERENCES;

Ardakani, M.S. and A.D. McLaren. 1977. Absence of local equilibrium duringammonium transport in a soil column. Soil Sci. Soc. Am. J. 41:877-879.

Arnold, P.W. 1959. Potassium uptake by cation exchange resins from soils andminerals. Nature 182:1594-1595.

Barshad, I. 1954. Cation exchange in micaceous minerals: II. Replaceability ofammonium and potassium from vermiculite, biotite and montmorillonite.Soil Sci. 78:57-76.

Chien, S.H. and W.R. Clayton. 1980. Application of Elovich equation to thekinetics of phosphate release and sorption in soils. Soil Sci. Soc. Am. J.44:265-268.

Chute, J.H. and J.P. Quirk. 1967. Diffusion of potassium from mica-like clayminerals. Nature 213:1156-1157.

Feigenbaum, S., R. Edelstein and I. Shainberg. 1981. Release rate of potassiumand structural cations from micas to ion exchangers in dilute solutions. SoilSci. Soc. Am. J. 45:501-506.

Feigenbaum, S. and R. Levy. 1977. Potassium release in some saline soils ofIsrael. Geoderma 19:159-169.

Havlin, J.L. and D.G. Westfall 1985. Potassium release kinetics and plantresponse in calcareous soils. Soil Sci. Soc. Am. J. 49:366-370.

Havlin, J.L., D.G. Westfall and R.S. Olsen. 1985. Mathematical models forpotassium release kinetics in calcareous soils. Soil Sci. Soc. Am. J. 9:371-377.

Dow

nloa

ded

by [

UQ

Lib

rary

] at

12:

29 0

5 N

ovem

ber

2014

KINETICS OF K DESORPTION 1371

Helfferich, F. 1962. Ion Exchange. McGraw-Hill, New York, NY.

Jardine, P.M. and D.L. Sparks. 1984. Potassium-calcium exchange in amultireactive soil system: I. Kinetics. Soil Sci. Soc. Am. J. 48:39-45.

Kilmer, V.J. and L.T. Alexander. 1949. Methods of making mechanical analysesof soils. Soil Sci. 68:15-24.

Malcom, R.L. and V.C. Kennedy. 1969. Rate of cation exchange on clay mineralsas determined by specific-ion electrode techniques. Soil Sci. Soc. Am. Proc.33:247-253.

Martin, H.W. and D.L. Sparks. 1983. Kinetics of nonexchangeable potassiumrelease from two Coastal Plain soils. Soil Sci. Soc. Am. J. 47:883-887.

Munn, D.A., L.P. Wilding and E.O. McLean. 1976. Potassium release from sand,silt and clay soil separates. Soil Sci. Soc. Am. J. 40:364-366.

Ogwada, R. A. and D.L. Sparks. 1985. A critical evaluation on the use of kineticsfor determining thermodynamics of ion exchange in soil. Soil Sci. Soc. Am.J. 50:300-305.

Okazaki, R., H.W. Smith and C.D. Moodie. 1963. Hydrolysis and salt-retentionerrors in conventional cation exchange capacity procedures. Soil Sci. 96:205-209.

Rao, P.S.C. and J.M. Davidson. 1978. Nonequilibrium conditions for ammoniumadsorption-desorption during flow-in soils. Soil Sci. Soc. Am. J. 42:668.

Rich, C.I. 1962. Removal of excess salt in cation-exchange capacitydeterminations. Soil Sci. 93:87-94.

Sawhney, B.L. 1966. Kinetics of cesium sorption by clay minerals. Soil Sci. Soc.Am. Proc. 30:565-569.

Selim, H.M., R.S. Mansell and L.W. Zelazny. 1976. Modeling reactions andtransport of potassium in soils. Soil Sci. 122:77-84.

Sivasubsramaniam, S. and O. Talibudeen. 1972. Potassium-aluminum exchangein acid soils: I. Kinetics. J. Soil Sci. 23:163-176.

Sparks, D.L. and P.M. Jardine. 1981. Thermodynamics of potassium exchange insoil using a kinetics approach. Soil Sci. Soc. Am. J. 45:1094-1099.

Sparks, D.L., D.C. Martens and L.W. Zelazny. 1980. Plant uptake and leachingof applied and indigenous potassium in Dothan soils. Agron. J. 72:551-555.

Dow

nloa

ded

by [

UQ

Lib

rary

] at

12:

29 0

5 N

ovem

ber

2014

1372 IOANNOU ET AL.

Sparks, D.L., L.W. Zelazny, and D.C. Martens. 1980. Kinetics of potassiumexchange in a Paleudult from the Coastal Plain of Virginia. Soil Sci. Soc.Am. J. 45:37-40.

Talibudeen, O. and S.K. Dey. 1968. Potassium reserves in British soils. Parts Iand II. J. Agric. Sci., Camb. 71, 95-104 and 405-411.

Talibudeen, O., J.D. Beasley, P. Lane and N. Rajendran. 1978. Assessment of soilpotassium reserves available to plant roots. Soil Sci. 29:207-218.

Dow

nloa

ded

by [

UQ

Lib

rary

] at

12:

29 0

5 N

ovem

ber

2014