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1 INTERNATIONAL STANDARD ISO First edition Dit docuent ag slechts op een stand-alone PC worden geinstalleerd. Gebruik op een netwerk is alleen. toestaan als een aanvullende licentieovereenkost voor netwerkgebruik et NEN is afgesloten. This docuent ay only be used on a stand-alone PC. Use in a network is only peritted when a suppleentary license agreeent for us in a network with NEN has been concluded. Soil quality - Deterination of the potential cation exchange capacity and exchangeable cations using bariu chloride solution buffered at ph = 8,l Quakt6 du so/ - Deterination de Ia capacite d khange ca tionique potentielle et des teneurs en cations khangeables en utilisant une solution tapon de chlorure de baryu 2 ph = 8,7 Reference nuber ISO 13536:1995(E)

2 ISO 13536:1995(E) Foreword ISO (the International Organization for Standardization) is a worldwide federation of national Standards bodies (ISO eber bodies). The work of preparing International Standards is norally carried out through ISO technical coittees. Esch eber body interested in a subject for which a technical coittee has been established has the right to be represented on that coittee. International organizations, governental and non-governental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Coission (IEC) on all atters of electrotechnical standardization. Draft International Standards adopted by the technical coittees are circulated to the eber bodies for voting. Publication as an International Standard requires approval by at least 75 % of the eber bodies casting a vote. International Standard ISO was prepared by Technicai Coittee lso/tc 190, Seil quality, Subcoittee SC 3, Cheical ethods and seil characteristics. Annex A of this International Standard is for inforation only. 0 ISO 1995 All rights reserved. Unless otherwise specified, no part of this publication ay be reproduced or utilized in any for or by any ean s, electronie or echanical, including photocopying and icrofil, without Perission in writing fro the publisher. International Organization for Standardization Case Postale 56 l Cl-l-l 211 Geneve 20 l Switzerland Printed in Switzerland

3 INTERNATIONAL STANDARD * ISO ISO 13536:1995(E) Soil quality - Deterination of the potential cation exchange capacity and exchangeable cations using bariu chloride Solution buffered at ph = 8,l WARNING - Bariu is a very toxic eleent if ingested. The bariu ion has health risks for laboratory personnel working with this Cheical; it is also harful for the environent. 1 Scope This International Standard specifies a ethod for the deterination of the potential cation exchange capacity (CEC) of soil buffered at ph = 8,1 and of the deterination of the content of exchangeable sodiu, potassiu, Calciu and agnesiu in soil. This International Standard is applicable to all types of air-dried soil saples. 2 Norative references The following Standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the tie of publication, the editions indicated were valid. All Standards are subject to revision, and Parties to agreeents based on this International Standard are encouraged to investigate the possibility of applying the ost recent editions of the Standards indicated below. Mebers of IEC and ISO aintain registers of currently valid International Standards. ISO 3696: 1987, Wa ter for analytical laboratory use - Specification and test ethods. ISO 11464: 1994, Soil quality - Pretreatent of saples for physico-cheical analyses. 3 Principle The deterination of CE@ as specified in this International Standard is a odification of the ethod proposed by Mehlich[ll,[*~ and odified by BascobW The CEC of soil saples is deterined in bariu chloride Solution buffered at ph = 8,l using triethanolaine. The soil is first saturated with respect to bariu by treating the soil three ties with buffered bariu chloride Solution. Subsequently, a known excess of 0,02 ol/1 agnesiu sulfate Solution is added. All the bariu present, in Solution as well as adsorbed, is precipitated in the for of highly insoluble bariu sulfate and the sites with exchangeable ions are then readily occupied by agnesiu. The excess agnesiu is deterined by either flae atoic absorption spectroetry (FAAS) or inductively coupled Plasa atoic eission spectroetry (ICP-AES). lt is also possible to deterine sodiu, potassiu, Calciu and agnesiu (and other eleents) in the bariu chloride extract of the soil. NOTES 1 Besides sodiu, potassiu, Calciu and agnesiu, it is also possible to deterine other cations, for exaple anganese, in the sae extract. 2 A yellowish-brown colour of the bariu chloride extract indicates that soe organic atter has been dissolved. Since organic atter contributes to the CEC, the easured value will be an underestiate of the potential CEC. 3 The su of exchangeable cations ay give a result that is greater than the CEC due to the dissolution of salts present in the soil. Preliinary washing of the soil with water to reove these salts should not be eployed be- Cause it could Change the relative proportions of cations in the CEC.

4 ISO 13536:1995(E) 0 ISO 4 Procedures 4.1 Leaching < 2 ), pretreated according to ISO 11464, into a tightly stoppered polyethylene centrifuge tube of about 50 l. Note the ass of the tube with cover and soil (I). Add 30 l of extraction Solution ( ) to the soil and Shake for 1 h. Balance the tubes and centrifuge at 3 OOOg for 10 in. 4.1.l Reagents Use only reagents of recognized analytical grade distil led water or deio nized water for all solutions. and Water, with a specific conductivity not higher than 02 S/ at 25 C (water conforing to Transfer the supernatant liquid to a 100 l voluetric flask. Repeat the addition of extraction Solution, shaking and centrifuging twice and adding the supernatant liquid to the 100 l voluetric flask on each occasion. Dilute to the volue of the voluetric flask with extraction Solution ( ) Bariu chloride solution, c(baci,) = 1 ol/l. Dissolve 244 g of bariu chloride dihydrate (BaC1,.2H,O) I n water and dilute to l with water Hydrochlorit acid, c(hci) = 2ol/l. Dilute 166 l of concentrated hydrochloric acid (p = 1,19 g/l) with water to l Triethanolaine solution, ph = 8,l. Dilute 90 l of triethanolaine (HOCH,CH,),N with water to about 1 litre and adjust the ph to 8,1 + 0,02 with about 140 l to 150 l of hydrichloric acid ( ). Dilute with water to 2 litres Extraction Solution. Mix equal volues of solutions and Protect this Solution fro exposure to carbon dioxide during storage Magnesiu sulfate Solution, c(mgs04) = 0,020 0 ol/l. Dissolve 4,930 g + 0,Ol g of agnesiu sulfate heptahydrate (MgSÖd.7H,0, see note 4) in water and dilute to l. NOTE 4 Magnesiu sulfate heptahydrate ay lose water of crystallization on standing. The reagent should be standardized by titration with ethylenediainetetraacetic acid (EDTA) at ph = 10 using Eriochroe Black T as the indicator. Alternatively the reagent ay be kept in a sealed polyethylene bag placed in a refrigerator Procedure Transfer 2,50 g to 5,00 g of air-dried soil with a high content of clay and/or huus, or 10 g of sandy soil or soil with a low content of huus (particle size Mix, filter through a coarse filter Paper (diaeter 7 c) and store the filtrate A for the deterination of sodiu, potassiu, Calciu and agnesiu following the procedure described in 4.3 and 4.4. Add approxiately 40 l of water (4.1.l.l) to the soil cake and Shake anually for 1 in to 2 in to break up the soil cake. Balance the tubes and centrifuge at about 3 OOOg for 10 in. Decant the supernatant to waste. Weigh the tube with its contents and cover (IzJ. Add 30 l of agnesiu sulfate Solution ( ) to the soil cake and Shake overnight. Balance the tubes and centrifuge at about 3 OOOg for 10 in. Decant the supernatant Solution through a coarse filter Paper (diaeter 7 c) into a conical flask and store the filtrate B for the deterination of agnesiu following the procedure described in Prepare a blank by following the procedure described above copletely, without the addition of soil. 4.2 Deterination of the CEC Principle An acidified lanthanu Solution is added to the filtrate B obtained according to the procedure described in and agnesiu is deterined by FAAS using an oxidizing (blue) airlacetylene flae. Lanthanu is added to prevent the foration of refractory copounds of agnesiu with Phosphate, aluiniu etc. in the flae Reagents Use only reagents of recognized analytical grade and distilled water or deionized water for all solutions Water, with a specific conductivity not higher than 0,2 S/ at 25 C (water conforing to Hydrochlorit acid, c(hci) = 12 ol/1 (p = 1,19 g/l). 2

5 0 ISO ISO 13536:1995(E) Magnesiu Standard solution, c(mg) = 0,001 0 ol/l. 1 is the ass of the centrifuge tube with air-dried soil, in gras, Pipette 50,O l of the 0,020 0 ol/1 agnesiu sulfate Solution ( ) into a l voluetric flask and dilute to the ark with water Acidified lanthanu solution, p(la) = 10 g/l. Dissolve 15,6 g of lanthanu nitrate hexahydrate La(N0,),-6~,01 in water in a 500 l voluetric flask, add 42 l of hydrochloric acid ( ) and dilute to the ark with water. is the ass of the centrifuge tube with wet soil, in gras. Calculate the cation exchange capacity (CEC) of the soil using the forula: where CEC = 3 OOO(Cb, - c*) CEC is the cation exchange capacity of the soil, in centioles positive Charge per kilogra; Calibration series is the corrected agnesiu concentration in the diluted filtrate B Solution, in illi- Pipette 0 l, 1 l, 2 l, 3 l, 4 l and 5 l of oles per litre; agnesiu Standard Solution ( ) into a series of 100 l voluetric flasks. Add 10 l of acidified cbl is the agnesiu concentration in the dilanthanu Solution ( ), to each flask, dilute to luted blank Solution, in illioles per litre; the ark with water and ix. These calibration solutions have agnesiu concentrations of 0 ol/l, is the ass of the air-dried Saple, in 0,Ol ol/l, 0,02 ol/l, 0,03 ol/l, 0,04 ol/l gras. and 0,05 ol/l, respectively. If the CEC exceeds 40 col+/kg, repeat the deterination using less soil, aending the calculation ac Procedure cordingly. Pipette 0,20 l of filtrate B of the soil saples (sec 4.1.2) and of the blank (see 4.1.2) into individual 100 l voluetric flasks. Add 10 l of acidified lanthanu Solution ( ) to each flask, dilute to the ark with water and ix. NOTE 5 The unit centioles positive Charge per kilogra, written in abbreviated for as col+/kg, is nuerically equal to the forerly used unit of illi-equivalents per hundred gras. Deterine the agnesiu concentration in the diluted filtrate B (c,) and the diluted blank (cbi) using the calibration solutions (4.2.3) and FAAS at wavelength 285,2 n, with the instruent set according to the anufacturer s instructions for Optiu perforante with an oxidizing (blue) airlacetylene flae Calculation Correct the concentration of agnesiu in filtrate B for dilution by the liquid retained in the centrifuged soil after being treated with water using the forula: where c2 = Cl (30 + Q - rnl> 30 Cl is the agnesiu concentration in the diluted filtrate B, in illioles per litre; is the corrected agn es iu concentration in the diluted fi ltrate B 1 in illioles per litre; 4.3 Deterination of exchangeable sodiu and potassiu Principle Sodiu and potassiu are easured in an acidified bariu chloride-triethanolaine extract of soil saples by flae eission spectroetry. NOTE 6 Because of the high bariu concentration in the ediu, ionization interferences are eliinated Reagents Use only reagents of recognized analytical grade and distilled water or deionized water for all solutions Water, with a specific conductivity not higher than 0,2 S/ at 25 C (water conforing to

6 ISO 13536:1995(E) 0 ISO Potassiu and sodiu stock Solution, p(k) = g/1 and p(na) = 400 g/l. Dissolve 1,906 8 g of potassiu chloride and 1,016 8 g of sodiu chloride in water. Transfer to a l voluetric flask and dilute to the ark with water. NOTE 7 Pulverize the potassiu chloride and sodiu chloride, heat the powders obtained either at 400 C to 500 C for at least 8 h or at about 200 C for 24 h, and cool the powders in a desiccator before use Diluted stock solution, p(k) = 100 g/1 and p(na) = 40 g/l. Pipette 25,0 l of the stock Solution ( ) into a 250 l voluetric flask and dilute to the ark with water Hydrochlorit acid, c(hci) = 1 ol/l. Dilute 83 l of concentrated hydrochloric acid (p = 1,19 g/l) to l with water Calibration series Pipette 0 l, 5 l, 10 l, 15 l 20 l and 25 l of the diluted stock Solution ( ) into individual 50 l voluetric flasks. Add IO,0 l of extraction Solution ( ) and 5,0 l of hydrochloric acid ( ). Dilute to the ark with water. These calibration solutions have potassiu concentrations of 0 g/l 10 g/l, 20 g/l, 30 g/l, 40 g/1 and 50 g/1 and sodiu concentrations of 0 g/l, 4 g/l, 8 g/l, 12 g/l, 16 g/1 and 20 g/l, respectively Calculations Calculate the exchangeable sodiu and potassiu contents in the soil saples using the equations: where b(na, exch) = h(k, exch) = 2l 1 74 g(& - &Q) 1,278 8(P3 - Pb2) h(na, exch) is the content of exchangeable sodiu in the soil, in centioles positive Charge per kilogra; b(k, exch) is the content of exchangeable potassiu in the soil, in centioles positive Charge per kilogra; P3 is the concentration of sodiu or potassiu in the diluted filtrate A, in illigras per litre; Pb2 is the concentration of sodiu or potassiu in the diluted blank solutions, in illigras per litre; is the ass of air-dried soil, in gras. 4.4 Deterination of exchangeable Calciu and agnesiu Principle Magnesiu and Calciu are deterined in the acidified bariu chloride triethanolaine extract by FAAS Procedure Pipette 2,0 l of filtrate A (see 4.1.2) and of the blank extract (see 4.1.2) into individual test tubes. Add 1,O l of hydrochloric acid ( ) followed by 7,0 l of water to each test tube and ix. Deterine the concentrations of sodiu and potassiu in the diluted filtrate A, blank and calibration solutions by flae eission spectroetry at wavelengths of 589 n and 766 n, respectively, using an airlpropane flae. NOTES 8 To prevent containation with sodiu, clean the glassware by soaking it overnight in 4 ol/1 nitric acid, technical grade. 9 Recheck the sta ndard with the highest concentration frequently (e. g. after every five eas ureents). NOTE 10 Due to the high bariu concentration in this ediu, there is no foration of refractory copounds of agnesiu or Calciu with Phosphate, aluiniu, etc. in the flae Reagents Use only reagents of recognized analytical grade and distilled water or deionized water for all solutions Water, with a specific conductivity not higher than 0,2 S/ at 25 C (water conforing to Hydrochlorit acid, c(hcl) = 4 rnolji. Dilute 330 l of concentrated hydrochloric acid (p = IJ9 g/l) to l with watet-. 4

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