Egypt. J . Suil Sci. 28, No. 4, pp. 397-406 (1988)

1 V Ycvta8sium Selectivity in Relation to the M i n e d o - - ! , fi

gical Composition of Some Alluvial Soils d Egypt ,,I ,I

"-

M.A. Abdel-Haanid, R.R. Shahin and R.E.A. Sabrah

Soil Science D q a r t m n t , Fac. Ag*., Cairo Univ.,

Egypt .

SOIL clays (< 1 and 2-1 p) and silt (20-2 fi) fractions show a, different preference for K-selectivity (kG). The relationship between K-selectivity and ]IT-satoretion % (kS) for all the investigated soils, mechanical separates and reference clay minerals was found to be of power type (kG = a kS-b).

Differences in kG values appear to be determined by clay minerals present in each fraction. The kG valuea of 2-1 and 20-2 p fractions were higher than those for < 1 p clays a t any percent of K-saturation which corres- ponds to the high amount of vermiculite and illite present in 2-1 fi and 20-2 fi fractions compared to < 1 p clays. Potassium selectivity (kG) was relatively eonstant when K-saturation exceeded 10 % for soils and < 1 p clays, and 15 70 for 2-1 fi clays and silt (20-2 fi) fractions. Eased an the K-eelectivity values, the retention and/or the avail- ability of soil-K to plant uptake was also discussed.

Key word^ : K-selectivity, K-saturation, mineralogy, alluvial soils.

Uptake of potassium from soils depends on complex equilibria between minerals-K, exchangeable-K and solution-K. Science soih vary in their mineralogical composition, equilibrium activities of K vary from soil to soil. Add to these variations in chemical behaviour of other nutrient ions in soil systems, so equilibria gov-

d erBning K uptake become increasingly complex.

Cation exchange equilibria with various cation pairs in soils and clays have received the attention of many workers. Recently, Bolt et al. (1963) ; Rich & Black (1964) ; Carson & Dixon (1972) ; Schalscha et d. (1975 & Hons et al. (1976), have reported ex- change equilibria data for K-Ca ion pair in soils and clays.

The selectivity coefficient of K appears to be helpful in quanti- fying relative adsorption affinity of K versus Ca which can be a factor in the retention and/or the availability of K in soils.

398 M.A. ABDEL-HAMID et al.

K-Ca exchange equilibria in the alluvial soils of Egypt are notclearly understood. Thus, a study of the K-Ca exchange equilibriain these soils seemed appropriate.

The objectives of this study aim to determine i) K/Caselectivity of some alluvial soils in Egypt, ii) K/Ca selectivityof the < Ill. 2-1 p" and 20-2fL, fractions separated from these sonssoils and iii) the relationships between K/Ca selectivity and themineralogical composition of these fractions.

Material and Methods

7.3 20.8 27.1 18.9 25.9 3.01.9 21.7 43.0 13.3 20.1 2,7

45.7 17.3 12.8 9.5 12.7 3.7

Four surface alluvial soil samples (0-30 em depth) from Egyptwere used for the present study and subjected to the determinationof particle size distribution according to Piper (1950). Also bento­nite, illite, vermiculite and kaolinite clay minerals were included forcomparison (Table 1).

TABLE 1. Deseription of the investigated samples.

---------------------------------- --------------------~--~-----particle size distribution %

Sample Location C,S F.S silt clay clay EKP2-.2 .2-.02 2-20 2-1 <1

mm mm ...u ).l )1

------------------------------------------------_.~-------------~!!!!~Clay Rosseta,EgyptClay Loam Zefta ,EygptSandy Clay T~el-Kebier,

Loam EgyptSandy Clay Aswan ,Egypt 10.9 52.2 11.5 9.8 15.6 3.9

-~!!~~---------------------------------------------------------£!~L~!!!!!:~!~Vermiculite Hafafit,Egypt .Illite Morris, Illinois, USABentonite Myknos, GleceKaolinite Hopkin a: Williams, London__1~~=~11 _

< 1 p" 2-1 JL and 20-2 fL fractions were separated from thesoil samples according to Jackson (1956). X-ray diffractograms.of the different soil separates ~ere obtained using a PhilipsX-ray diffractometer, and interpreted on the basis outlined byWhittig & Jackson (1955) and Brown (1961). Semi-quantitativeestimation of the clay mineral and accessory minerals was carried

Egypt. J. Soil Sci. 28, No. 4 (1988)

POTASSIUM SELECTIVITY IN RELATION TO ... 399

out using the peak area according to Gjems (1967). The mine­ralogical composition of all separates are presented in Table 2.Soil samples and their mechanical separates as well as referenceclay minerals were subjected to the determination of K-selectivity.

.TABLE 2. Mineralogical composition of the soil separates <as per cent ofthe fraction).

----------------------------------------------------------Site Ints K V Ch I Mt Int-

O F(I-V) Mt.--------------------------- -----------------------------

Ro:;seta 6 6 3 1 1 7 54 9 2 1clay Zefta 6 6 4 10 6 56, 8 2. 2

<1 Tl:Ilel-Kebier 9 6 8 11 6 50 .8 1-U

Aswan 6 17 12 6 58

Rosseta 4 19 6 1" 12 35 1 1clay Zefta 4 11 9 14 10 34 9 92-1P T~iel-Kebier 3 10 8 12 16 25 9 8 10

Aswan 3 21 8 13 12 35 6 2----------------------------------------------------------

Rosseta 8 6 13 14 9 20 30silt Zefta 8 12 12 11 21 3620-2)l Telel-Kebier 10 8 17 9 20 36

Aswan 26 10 10 15 20 13 6---~----------_._------------------------------------- -- -

Ints(I-V)=interstatified(illite-vermiculite),K: kaolinite,r:vermiculite, Ch=chlorite, I:illite, Mt:montmorillonite ,Int-Mt:interlayered montmrillonite, Q:quartz, F:feldspars.

The K-selectivity coefficient, Kg based on the Gapon equa­tion, was determined according to the method of Carson & Dixon(1972) was calculated as follows :

kGK+ (sorbed)

Ca + + (sorbed

K+ (solution)

Ca + + (solution) t

The sorbed cations expressed as milliequivalents per 100 g andthe cations in solution as mole per liter. The selectivity valueexpressed in this paper bears the dimensions of (liter mole l j.

Egypt. J. Soil Sci. 28, No. 4 (1988)

400 M.A. ABDEL-HAMID et al.

Results and Discussion

Data presented in Table 3 and 4 and Fig. 1 and 2 revealedthat potassium selectivity values (kG) of all clay minerals andsoil separates increased as K-saturation (kS) is low, and declinegradually but remain constant as K-saturation (kS) increases. Thebest fitting equation of such relationship was found to be of powertype (KG = a Ks-b).

fABLE 3. Potassium seledivity coefficient (kG) in Iitre/mole)~ versus K­saturation % (kS) for the investigated clay minerals.

~----------------------------~----------------------

vermiculite illi te bentonite kaolinite

._--~~---~g------~~---~g-----~§---~g------~§---~Q_._-5.5 40.8 3. 1 37.1 1.5 10.0 1• 1 1.5

10.1 26.1 7.5 25.0 3.5 7.2 1.5 1.015.5 13.2 1,. 5 11.5 5.6 4.0 3.0 0.627.5 12.1 22.4 10.5 16.1 3.6 9.1 0.536.2 11.4 33.5 9.5 28.5 3.2 20.2 0.4

----------------------------------------------------Values of kG for the reference clay minerals (Table 3 and

Fig. 1) indicated that vermiculite and illite minerals were themost highly selective, bentonite was moderately selective andkaolinite was the least with a very low selective value for K+. Thehigh ability of micaceous minerals to selective K+ is probablydue to that there are specific sorption sites for K+ in these mine­rals (Bolt ei al., 1963). These wedge shaped places occur at fray­ed edges or deeper within the weathered mica particles. If weather­ing is initiated simultaneously from all sites and all layers arenot stripped K+, there are probably many places where strippedlayers do not "match" in the interior. Such a model could explainwhy K+ can be fixed in vermiculite (Rich and Blach, 1964).

Vermiculite and illite minerals extented a high preference forK+ over a wide range of K-saturation percentage (kS). Theyexerted high K-selectivity (kG;;.. 12 and 10, respectively) at lessthan 15% kS. Potassium selectivity values for bentonite werelow for greater than 5'70 K-saturation, it exceeded a value of kG;:. 4 for the first 1 to 5% of the exchange capacity. Kaoliniteexceeded kG ~ 0.5 only at less than 3% K-saturation (kS).

Bgypt. J. Soil Sci. 28, No. 4 (1988)

POTASSIUM SELECTIVITY IN RELATION TO ... 401

4

x----.c YEllMlCUUlEo olWTE....--... BENTONITE• • KMlUKlTE

...zIII

tf'"0u~...>;::u B!!t...... .4

05 10 15 20 21) 30 JI) ~

Il.-SAlWlAIIQN ~

Pig. 1. Relationship between K-selectivity coefficient kG and K-saturationas % of CEC for the studied clay minerals.

Potassium selectivity of the clays « 1 p, and 2.1 p, and silt(20-2 p,) fractions show a different preference for K+ (Table 4).

Differences in kG values appear to be determined by clay mineralspresent in each fraction (Table 2).

The kG versus K-saturation curves (Fig. 2) were similar amongthe < 1p, clays as their mineralogical composition was relativelyuniform, where 2-1 JL clays and silt fractions differ due to thevariation in their mineralogical composition. The kG values of

~ the < 1 JL clays were lower than those of 2-1 JL and silt fractionsat any percent of K-saturation. This can be rendered to the factthat the < 1 P, contained lower amount of illite and vermiculiteminerals as well as to the influence of the dominancy of mont­morillonite in this fraction (Table 2). On the other hand, the kGvalues for the silt and 2-1 JL fractions were high due to the highamount of illite and vermiculite and the paucity of montmorillonitein these fractions, especially in the silt fraction.

Egypt. J. Soil Sci. 28, No. 4 (1988)

402 M.A. ABDEL-HAMID et aL

TABLE 4. Potassium selectivity coefficient (kG) in liter mole)~ versus K­saturation % (kS) for the investigated soils and soil separates.

Rosseta 2.4 21.7 4.4 35.2 1.5 38.2 3.5 18.94.0 16.7 7.5 23.3 4.0 28.4 5.0 13.05.3 7.4 9.9 12.6 6.1 13.2 5.5 5.88.8 5.4 14.3 5.6 13.0 7.1 9.0 4.2

22.4 4.0 35.0 3.4 34.5 5.6 21.5 3.6----------------------------------~-------------------- --

Zefta 3.9 23.8 6.5 38.6 4.1 38.0 3.0 lB.l

5.3 18.4 7.5 29.2 8.5 27.4 4.1 11.26.3 10.8 9.0 16. 1 7.9 18. 1 7.0 7.39.5 6.0 14.1 9.3 12.6 9.2 8.7 4.0

25.2 4.9 37.4 7.4 34.1 6.4 22.5 3.5-------------------------~----------------------------- - -

Telel- 1.6 15. 1 5.5 36.4- 5.9 4.0.0 4.6 19.4'Kebier 2.0 9.2 6.2 28.-4 B.9 27.6 5.0 19.8

5.0 5.2 12.3 13.2 13.1 16.8 7.6 7.fl9.7 4.0 17.4 9.5 15.0 11.5 9.0 5.4

17.8 2.6 40.0 8.0 36.5 10.0 24.8 4.5----_._-----------------------_._------------------------

Aswan 1.6 14.0 3.5 34.1 5.0 40.5 2.5 18.62.0 9.6 6. 1 23.3 6. 1 23.' 3.8 14.84.5 4.2 9. 1 9.9 9.0 11.4 4.5 9.87.5 3.8 11.6 6.2 14.9 6.9 8.5 3.8

16.1 2.6 36.6 4.0 35. 1 4.4 20.8 2.8------_.------------------_._------------------------- - - - - ---

The < 1 P. samples exterted a high preference for K + over anarrow range of K-saturation % than the 2-1p. and silt fractions.The selectivity values of < 1 P. samples exceeded a value of 4 foronly the first 1 to 9% of the exchange capacity. The < 1 p. frac­tion separated from Tel el-Kebier soil showed a relative increasein kG values, as they exceeded 5.4 for the first 1-9% K-saturation.This relative. increase may be attributed to that the < 1 Jl, frac­tion separated from Tel el-Kebier soil contained much more ver­miculite and interstratified minerals (illitevermiculite) than thatseparated from the other soils.

Egypt. J. Soil Sci. 28, No.4 (1988)

POTASSIUM SELECTIVITY j:-< RELATlON TO ... 403

SILT lO-l ~

CLAY <'.lJ.

IS ao 2S 3D 3S ~~I( -SATu,,,,,nOl4 ~

:x--« RossetA__ Zen.0----4 Telel-~ebi.r

--. A••an

S04L

CLAY 2-1~

...Z

~ 12

~u

,.....s;: 12....~'" 8'",'" ~

Fig. 2. K-seleetivity coefficient (kG) versus k-saturation (kS) for the in­vestigated soils and fractions.

The highest selectivity values of the 2-1 p. and silt fractionswere present at K-saturation less than 15%. The 2-1 .po clay andsilt (20-2 p.,) fractions separated from Tel el-Kebier soil have the

Egypt. J: Soil Sci. 28, No 4 (198~)

M.A. ABDEL-HAMID et al.

highest value of kG, as 85% of the exchange sites of these frac­tions have selectivity values (kG) below 11 and 10, respectively.The lowest values of kG were found in the 2-1 jJ, and silt fractionsseparated from Aswan and Rosseta soils (as 85% of the exchangesites exhibit selectivity values below 6.5 and 5.5 of the clay (2-1 j.t)

and silt (20-2 j.t). respectively). These results are mainly due tothe influence of paucity of kaolinite and montmorillonite in the 2-1j.t and 20-2 j.t fractions separated from Tel el-Kebier soil corres­ponding to those fractions separated from Aswan and Rossetasoils.

The results of kG for the whole soils (Table 4 and Fig. 2) in­dicated that Zefta clay loam and Rosseta clay soils exhibited thehighest K-selectivity values, as about 90% of the exchange siteshave selectivity value below 6 and 5, respectively. This is sub­stantial agreement with the high amount of silt (20-2 p.) and clay(2-1 j.t) fractions, which have the highest ability to K-selectivity dueto their mineralogical composition. Tel el-Kebier and Aswan soilsshowed low K-selectivity values, as about 90% of their exchangesites have kG below 35 and 3, respectively. This is probably dueto the dominancy of sands (> 60%) which is mainly consisted ofinert quartz and feldspars.

The high kG values that occur over several percent of K-satu­ration in clays (2-1fA-l and silt (20-2 fA-) fractions indicated thatthese fractions were more important than < 1 fA- fraction in con­trolling kG values and consequently K+ availability to plants.

In conclusion, it would appear from soil K-seiectivity datathat K+ becomes more available with adding supplemental K + asfertilizer. The lowest the K-selectivity values the highest theK-availability of the soil. The data indicated that the investigatedalluvial soils should have 6 to 10% K-saturation, depending onthe content of K-selective minerals (i.e. illite, vermiculite, and in­terstratified minerals "illite-vermiculite"). to provide adequate po­tassium nutrition for growing plants. It was found that the in­vestigated soils had < 4'70 K-saturation and so high K-selectivity.This means that the first addition of K-fertilizers may suffer fromhigh selectivity of such soils until the K-saturation % exceed theappropriate limits.

Egypt. J. Soil Sei. 28, No.4 (1988)

POTASSIUM SELECTIVITY IN RELATION TO '" 405

Reference.

Bolt, G.H., Sumner, M.E. and Kamphorst, A. (HI63) A study of the equili­bria between three categories of potassium in an iIIitic soil. SoH Sci.Soc. Am. Proe, 27, 294.

Brown, G. (1961) «The X-ray Identification and Crystal Structures of ClayMinerals». Miner. Soc. (Clay, Miner, Group), London.

Carson, C.D. and Dixson, J.B. (1972) Potassium selectivity in certain mont­morillonite soil clays. Soil Sci. Soc. Am. Proe, 36, 838.

Gjems, O. (1967) Studies on clay minerals and clay mineral formation insoil profiles in Scandinavia. J ordunder SokeIsns Sertykk, N.R., 128,306.

Hons, F.M., Dixon, J.B. and Matoeha, J.E. (1976) Potassium sources andavailability in a deep sandy soil of East Texas. Soil Sci. Soc. Am. J. 40,370.

Jackson, M.L. (1966) «Soil Chemical Analysis», Advanced Course Publ. bythe author, Dept. Soil Sci., University of Wisconsin, Madison, Wisconsin.

Piper, C.S. (1960) «Soils and Plant Analysis». Inter. Sci. Publ. Inc., N.Y.

Rich, C.I. and Black, W.R. (1964) Potassium exchange as affected by ca­tion size, pH, and mineral structure. Soil Sci. 97, 384.

Schalseha, E.B., Pratt, P.F. and De Andrade, L. (1976) Potassium-calciumexchange equilibria in volcanic-ash soils. Soil Sci. Soc. Am. Pree, 39,1069.

Whitting, L.D. and Jackson, M.L. (1966) Interstratified layer silicates in somesoils of northern Wisconsin. Clay and Clay Miller. 3, 322.

(Reeehecl 10/1986)

Egypt. J. Soil Sci. 28, No. 4 (1988)

406 M.A. ABDEL-HAMID et al,

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Egypt. J. SoH Sci. 28, No.4 (1988)