Kinetics of Potassium Adsorption and Desorption in

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Some chemical and physical properties are determined. Soils were classified according to key to soil taxonomy. Potassium adsorption- desorption experiments ...
MAGNT Research Report (ISSN. 1444-8939)

Vol.3 (3). PP: 118-124

Kinetics of Potassium Adsorption and Desorption in some Vertisols of Duhok GovernorateKurdistan Region- Iraq Mohammed Ali Jamal Al-Obaidi1, Mohammed Ali Fayyadh2* and Abdulrahman Semo Hussien3 1 Department of Soil & Water Resources, College of Agriculture and Forestry, University of Mosul, Mosul- Iraq 2 Department of Soil & Water Science, Faculty of Agriculture and Forestry, University of Duhok, Duhok, Kurdistan Region– Iraq 3 Shingal Technical Institute, Polytechnic University- Duhok, Kurdistan Region- Iraq * Correspondence author Published Online: March issue. 2015 Abstract: Twelve soils were sampled within vertisols (Chromic Haploxererts) order in Duhok governorate of kurdistan region, Iraq. Some chemical and physical properties are determined. Soils were classified according to key to soil taxonomy. Potassium adsorption- desorption experiments were carried out by using miscible displacement technique. The potassium adsorption capacity in studied soil samples, were ranged from 543 to 1255 mg.Kg-1, the low value was recorded in soil sample 3 of Simeil pedon , while the high value was recorded in soil sample 7 of Bateel pedon. The variation of potassium adsorption in studied soils reflects the differences in physiochemical and mineralogical properties. The rate coefficients of K- adsorption were ranged between 12- 54 x10-3 min-1 with an average 24x10-3 min -1. Soil potassium desorption in studied soil samples, were ranged from 37 to 207 mg Kg -1 with mean value 112 mg.Kg-1. The similarity in release rate constants in some soil samples could be due to similarity in mineralogical composition in clay as well as in silt fraction.

Keywords: adsorption, desorption, kinetic potassium, vertisols 1. Introduction Potassium is an essential nutritive element for all plants (Mengel, et al, 2001, White, 2003) and it’s availability in soil is limited by soil texture, clay minerals, moisture content , rate of fertilizers (Samadi, 2006, Simonsson, et al., 2007) and fertilizer management (Krauss, 2003). The rate of K+- adsorption after fertilizer addition differs among soils because the response of crops to the applied potassium are earlier and thus it’s unpredictability is due to different adsorption characteristics of potassium by various soils. Depending upon the amount and type of clay minerals, up to 57% of the applied potassium can be adsorbed by the clay colloids (Shanwall and Dahiya, 2006). Amount of potassium adsorbed on clay particles depend upon kinetic and thermodynamic factors (Du, et al, 2004). Soils with high potassium specificity like Illite and vermiculite rich soils (Karabachsch and Ulrich, 2007). Similarly, the rate of potassium adsorption on Illite and Vermiculite was reported to be much slower than Montmorilonite and Kaolinite (Jalali, 2007, Al- Azawi, 2010). Some of clay minerals like smectite and Kaolonite easily release all of their adsorbed potassium than Illite and Vermiculite (Gosh and Sing, 2001), upon the rate

of removal by plants and rapidity at which potassium can be desorbed from the adsorbed phase where as initial adsorption equilibrium solution levels serves as an index of potassium release (availability ) (Roa, et al, 2004, Jalali, 2006). This equilibrium of potassium concentration appears to provide a better index of soil fertility. A knowledge about the variation in K+- adsorption among soils and the equilibrium between solid- liquid phases of K+ is necessary to predict the adsorption index of added K+fertilizers in soils to make precise K+- fertilizers recommendations (Shanwall, 2006, poonia and Nicderbudde, 2007, Roa and taker, 2007) There is a little information available to K+ - adsorptiondesorption in Iraqi soils. Vertisols are important soil resources in Mediterranean region. These soils have a high CEC and retain great amounts of Potassium in exchangeable form (Dhillon, et al, 1989). Plants grown in the soils, especially summers crops show a positive response, in vertisols due to their high content of expanding clay minerals, because cracked when dry, causing some damage to the root system and difficulties in their management. Potassium release from soil affected by water management, schemes involves periods of wetting. (DOI: dx.doi.org/14.9831/1444-8939.2015/3-3/MAGNT.20)

MAGNT Research Report (ISSN. 1444-8939)

Vol.3 (3). PP: 118-124

at rate of 1 ml.min-1 until equilibrium was reached later (to remove Kex from the soil sample). K+ adsorption: The Ca2+ saturated soil was leached by using 0.01 M KCl solution supplied as steady rate to renew the soil solution and to assess K+adsorption at constant K+ concentration in the soil solution. The solution was leached at the rate of constant K+-concentration in the soil solution. The solution was leached at the rate of 1 ml.min-1for each 10 minutes. The difference between initial and final K+ is adsorbed by the soil. K+ desorption: The K+- desorption was then initiated by using 0.01 M CaCl2, the solution of CaCl2, was passed through the soil at rate1 ml.min1 for each 10 minutes. The quantity of K+ in the solution for both adsorption and desorption studies was measured by flame photometer. Desorption index: According to Marzadori et. al., (1991), desorption index was calculated by using the following formula: DI= md / ma x 100 Where: DI: Desorption Index. md: Desorption isotherm slope. ma: Adsorption isotherm slope.

Vertisols occur in almost every major climatic zone of the world with their distinctive properties such as shrinking and cracking when dry and swelling when wet are some of the main features affecting their use and management. (Ahmed and Mermut, 1996). Materials and Methods Twelve soils were sampled within vertisols (Chromic Haploxererts) order in Duhok governorate in kurdistan region, Iraq. Soil samples where air- dried, grinded and pass through 2 mm sieve. Some chemical and physical properties are determined as in Carter and Gregorich, (2008) (Table 1 and 2). Soils were classified according to key to soil taxonomy (Anonymous, 2006) (Table 3). Potassium adsorption- desorption experiments were carried out by using miscible displacement technique as mentioned by Cracksi and Sparks, (1985); Shanwall, (2006) and can be summarized as follows: Calcium saturation: 10 gm of soil samples placed into 47 mm Nucleopore filter- column. The samples where saturated with 0.1 M CaCl2 solution

Table (1): Some physical and chemical properties of studied soils Location (Pedon)

Simeil

Bateel

Zakho

Sample No.

pH

EC ds.m-1

Sand

1 2 3 4 ______ 5 6 7 8 ______ 9 10 11 12

7.9 7.8 7.7 7.8 ___ 7.9 7.7 7.8 7.6 ___ 8.0 7.6 8.1 7.9

0.5 0.5 0.4 0.5 ______ 0.3 0.6 0.6 0.8 ______ 0.3 0.3 0.4 0.4

140 130 25 120 ______ 75 125 120 110 ______ 200 180 140 220

Silt 380 415 480 490 ____ 510 515 500 550 ____ 440 470 450 400

Organic Total Active matter CaCO3 CaCO3 gm.Kg-1 480 13 115 45 455 20 165 45 495 12 173 65 390 14 182 91 ______ ______ ______ ____ 415 16 221 52 360 15 291 65 380 12 282 45 310 12 261 55 ______ ______ ______ ____ 360 21 225 60 350 13 196 65 410 14 231 54 380 15 230 51

Clay

CEC CmoleC.Kg-1 41.2 37 25 20 ___________ 26 30.2 29.1 30.8 ___________ 28 24.4 28.5 28.9

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Table (2): Chemical properties and semi-quantitative amount of clay minerals in studied soils Location (Pedon)

Sample No.

Soluble K+

Exchange K+

NonExchange K+

CmoleC.Kg-1 1 2 3 4 5 6 7 8 9 10 11 12

Simeil

Bateel

Zakho

0.011 0.005 0.003 0.010 0.003 0.004 0.011 0.007 0.003 0.011 0.006 0.005

0.75 0.73 0.49 0.93 0.53 0.51 0.73 0.57 0.48 0.54 0.4 0.31

1.29 1.16 0.91 3.46 2.06 0.96 1.47 1.34 0.74 0.91 0.61 0.28

Clay Minerals % Illite

Smectite

Vermiculite

Kaolinte

20 30 33 29 22 22 27 38 30 14 19 21

19 31 27 20 30 21 18 17 31 22 25 20

13 5 12 17 10 14 21 13 15 19 14 11

20 21 26 32 22 29 21 19 22 21 19 22

Table (3): Classification of studied soils at family level according to USDA- Soil taxonomy Location

Sample

(Pedon)

No.

Soil Family

1

Fine Clay, Smectitic, Superactive, Calcaraous, thermic, Cracked, Chromic Haploxererts.

2

Fine Clay, Smectitic, Superactive, Calcaraous, thermic, Cracked, Chromic Haploxererts.

3

Fine Clay, Smectitic, Active, Calcaraous, thermic, Cracked, Chromic Haploxererts.

4

Fine Clay, Smectitic, Active, Calcaraous, thermic, Cracked, Chromic Haploxererts.

5

Fine Clay, Smectitic, Superactive, Calcaraous, Hyperthermic, Cracked, Chromic Haploxererts.

6

Fine Clay, Smectitic, Superactive, Calcaraous, Hyperthermic, Cracked, Chromic Haploxererts.

7

Fine Clay, Smectitic, Superactive, Calcaraous, Hyperthermic, Cracked, Chromic Haploxererts.

8

Fine Clay, Smectitic, Superactive, Calcaraous, Hyperthermic, Cracked, Chromic Haploxererts.

9

Fine Clay, Smectitic, Superactive, Calcaraous, thermic, Cracked, Chromic Haploxererts.

10

Fine Clay, Smectitic, Superactive, Calcaraous, thermic, Cracked, Chromic Haploxererts.

11

Fine Clay, Smectitic, Superactive, Calcaraous, thermic, d Cracked, Chromic Haploxererts.

12

Fine Clay, Smectitic, Superactive, Calcaraous, thermic, Cracked, Chromic Haploxererts.

Simeil

Bateel

Zakho

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MAGNT Research Report (ISSN. 1444-8939)

Results and Discussion K-Adsorption capacity The potassium adsorption capacity in studied soil samples by using miscible displacement technique were ranged from 543 to 1255 mg.Kg-1. The low value was recorded in soil sample 3 of Simeil pedon, while the high value was recorded in soil sample 7 of Bateel pedon (Table 4). The variation of potassium adsorption in studied soils reflect the differences in physiochemical and mineralogical properties, as a result of existing illite and smectite minerals group, that are the dominant clay minerals in studied soil samples which causes potassium fixation. The rate of potassium adsorption after fertilizer added to the soils different among them, because the responses of crops to applied potassium are declined, this unpredictability is due to different adsorption

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characteristics of potassium by various soils. Depending upon the amount and type of clay minerals up to 57% of applied potassium can be adsorbed by soil colloids (Pal et al., 1999; Shanwall and Dahiya, 2006). Amount of potassium adsorbed on the clay particles depend on the kinetics and thermodynamic factors (Parffit, 1992; Schneider, 1997), soil with high potassium adsorption like illite and vermiculite (Goulding, 1987; Karabachsch and Ulrich, 2007). Sparks (2000) referred that in general considered that among clay and other silicates, mica and vermiculite have a high, while montmorilonite chlorite and kaolinite have a low potassium fixation capacity.

Table (4): Amount of Adsorbed- K and rate coefficients in studied soils Location (Pedon)

Sample No.

K- Adsorbed

Rate Coefficientx10-3min-1

1

772

23

2

579

18

3

543

25

4

590

21

5

641

18

6

676

34

7

1255

54

8

1161

13

9

1142

12

10

626

20

11

665

24

12

927

20

797

24

Simeil

Bateel

Zakho

Mean Rate Coefficient of K adsorption The kinetic model (first order) equation was used to describe K- adsorption in studied soils. Kadsorption coefficients were listed in table (4) . The rate coefficients of K- adsorption were ranged

between (12- 54) x10-3 min-1 with an average 24x10-3 min-1. The low rate coefficient of Ka was recorded in soil sample 9 in Zakho pedon 12 while the higher value was recorded in soil sample

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MAGNT Research Report (ISSN. 1444-8939)

7 in Bateel pedon (Table 4). The rate coefficient of K- adsorption on Illite and vermiculite was reported to be much slower than montmorillonite and kaolinite (Ogwada and Sparks, 1986b), while K- Desorption capacity The soil potassium desorption of studied soil samples by using miscible displacement technique, were ranged from 37 to 207 mg.Kg-1 in simeil pedon with mean value 112 mg.Kg-1 (Table 5). The variation of Kr values in studied soils reflects the role of physicochemical and mineralogical properties (Table 5), as a result of X-ray diffraction. The illite was major mineral in soil, which has high K- fixation; the variation of K release in studied soils may be attributed to the

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some of clay minerals like smectite and kaolinite easily release all of their adsorption K than do illite and vermiculite (Mengel and Uhlen becker, 1993; Ghosh and sing, 2001). difference in the energy of holding K with soil solid phase. The rate at which K is released from clay minerals in the soils is important in plant nutrition, many studies reported that clay fraction greatly affect the rate of desorption and correlate with the amount of K available in soils (Sparks et al., 1980; Jardine and Sparks, 1984; Havlin et al., 1985) as shown in table (5) all amounts of Kdesorbed were less than its adsorbed

Table (5): Amount of K- desorbed and rate coefficients of K- release (Kr) in studied soils. Location (Pedon)

Simeil

Bateel

Zakho

Sample No.

K- Desorbed

Krx10-4 min-1

DI m-1

1

85

37

0.13

2 3 4 5 6 7 8 9 10 11

37 207 66 65 82 118 159 38 174 57

122 13 79 17 20 51 3 87 5 217

0.68 0.05 0.38 0.09 0.58 0.94 0.02 0.73 0.03 0.92

12

152

90

0.46

112

61

Mean K- Rate Coefficient of release (Kr) Knowledge of the kinetics of K to property makes K- fertilizer recommendation especially in vertisols. Potassium release kinetics was studied employing first order reactions according to Sparks (1984). The K- release rate constant was listed in table (5). These values were ranged from 3x10-4 min-1 in soil sample 8 of Bateel pedon to 217x 10-4 min-1in soil sample 11 of Zakho pedon

with mean value 61x10-4 min-1 (Table 5). The similarity in release rate constants in some soil samples could be due to similarity in mineralogical composition of clay as well as in silt fraction. The higher release constants were observed in soil samples had high adsorption capacity. This could be due to higher exchangeable K-sites in soil surface.

Desorption Index This parameter is used according to the following equation. DI= (Kr/Ka) x100 Where: DI = Desorption index. Kr = Release constant from slope

of first order equation. Ka= Adsorption constant rate of first order equation. As shown in table (5), the DI values were ranged between 0.02 at Bateel pedon, soil sample 8 to

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MAGNT Research Report (ISSN. 1444-8939)

higher value 0.94 at the same location, soil sample 7. Depending on the results we can classified the studied soils according to its ability to release Kadsorbed into three groups Low, including the following soil samples (8-Bateel, 10- Zakho, 3Simeil, 5- Bateel, 1- Simeil). Moderately DI (4- Simeil, 12- Zakho, 6- Bateel) and high release power (7-Bateel, 11-Zakho, 9-Zakho, 2- Simeil).

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