THE pH OF STRONGLY ACID SOILS

Nichol, W. E.

doi:10.4141/cjss58-011

Cited by 5 publications

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“…The products of the latter reaction are polynuclear hydroxyaluminum cations, which will be referred to as Alpl, with an OH/A1 mole ratio equal to or near 2.5. If AlC13 is used instead of Al(C104)3 the reactions are the same, providing the C1-concentration is not too high (3), except that the ISP contains appreciable amounts of C1- (3,4) which retards the transformation of ISP to gibbsite.…”

Section: Introductionmentioning

confidence: 99%

A second species of polynuclear hydroxyaluminum cation, its formation and some of its properties

Turner

1976

Can. J. Chem.

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ROBERT C. TURNER. Can. J. Chem. 54,1910Chem. 54, (1976.When a solution of A1(CI04)3 or AICI, with total Al concentration between 5 X 10-4 and 6 X 1 0 -W is partially neutralized very slowly with a base, it is possible to produce a solution of polynuclear hydroxyaluminum cations with no solid phases present. When such a solution is aged, the polynuclear hydroxyaluminum cations, Alpl, disappear very slowly at 25 "C and a second type of polynuclear hydroxyaluminum cations, Alp-,, is formed. The second type, Alpz, has some properties that are the same as those of Alp1, e.g. they both have an OH/A1 mole ratio equal to or very nearly equal to 2.5, diffuse readily across a dialysis membrane, and are removed from solution by the clay mineral bentonite in an exchangeable form. Some of their properties, however, are entirely different, e.g. AIpI reacts with 8-hydroxyquinoline about 250 times faster with a much lower energy of activation than does Alp,, is much less resistant to attack by HC1, and is precipitated at a p H about 0.5 p H units lower than Alpz. The transformation of AlPI to Alpz is a first order process with an energy of activation of 20.8 kcal per mol. The specific rate constant seems to be affected somewhat by the extraneous anion present and the degree of neutralization; experimental values varied from 0.57 X 10-3 to 3.5 X 10-3 day-1 at 25 "C.

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Section: Introductionmentioning

confidence: 99%

A second species of polynuclear hydroxyaluminum cation, its formation and some of its properties

Turner

1976

Can. J. Chem.

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Studies on Soil Potassium

Beckett¹

1964

Journal of Soil Science

122

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The activity ratio U K / , / (~~+ % ) had the same value for all solutions in equilibrium with a chosen soil, regardless of their concentration (up to 0.06 M), or of the proportion of Ca to Mg.The activity ratio may be expected to provide a satisfactory measure of the ruling chemical potential of labile K in a soil, provided it is not used to compare soils of widely different Ca (and Mg) status, or a few soils of which the activity ratio is not independent of the concentration of the soil solution.

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SOURCES OF ERROR IN THE DETERMINATION OF SOIL POTASSIUM ACTIVITY RATIOS BY THE Q/I PROCEDURE

Moss¹,

Beckett

1971

Journal of Soil Science

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Equilibrium activity ratios such as aK/(atJ,,+m)t may be determined by analysing a solution in equilibrium with a soil. The Q/I procedure is one method for establishing the composition of such a solution. Several approximations have been proposed to simplify this procedure or the necessary calculations. This paper reviews the main sources of error in the Q/I procedure.Errors may arise in the sampling, preparation, and storage of soil samples: it is best to analyse samples as soon as possible after sampling, with no preparation other than gentle sieving.The Q/I procedure rests on certain implicit assumptions which will not strictly apply if there is any substantial exchange, between exchangeable cations and soluble salts or microbially dissolved carbonates, during determinations. This paper demonstrates that such exchange does indeed occur during the determination of the equilibrium activity ratios of soils at 5 < pH > 6, but that the errors may be ignored in British soils at pH > 5. Modified interpolation procedures designed to minimize errors from these causes appear to introduce larger errors than they avoid. ERRORS IN POTASSIUM ACTIVITY RATIOS 515ratios (ARF) by the Q/I procedure, and in the simplifying approximations to the full procedure.The Q/I procedure In the determination of ARK by the full Q/I method (Taylor, 1958; Beckett, 1964a) small replicate samples of soil are equilibrated with ali uots of a dilute CaC1, solution containing graded amounts of K, by equilibrium suspensions and analysed for K and (Ca+Mg). AK, the amount of K per unit weight of soil which has been lost or gained by the soil during equilibration, is calculated from the changes in comosition of each test solution. The final activity ratio of each solution sha 9, ing for short periods. Samples of solution are separated from the is calculated from its composition according to Country Malayat West Indies* Britain* Britain (K deficient)" Ireland* where square brackets are molar concentrations and 'f' are activit the value of ARF at AK = 0, is interpolated from a graph of AK against ARF. It is deemed to be the activity ratio of a solution which has not changed in composition on being added to the soil.TABLE I Range of cation concentrations in the soil solutions of topsoils at jkld moisture contentscoefficients (subscript f refers to equilibrium or final solutions). A&, 2 K I Ca+Mg pH range m M -0.03-0.38 0'01-0.95 4.61.0 0.04-3.64 3-1-11.7 4'57' 1 0*20-2*60 7'0-54'7 4 ' 7 4 . 7 0*01-0.15 2.9-15.9 limed and 0.6-9.56 13.3-39.1 K-fertilized 5x6 P. MOSS AND P. H. T. BECKETT Anderson et al., 1942; Le Roux and Sumner, 1967). The solutions should not be so strong that the Ratio Law (Schofield, 1947) may not apply. Blanchet (1959a, b) recommends a subsidiary experiment to determine the Ca concentration. Most workers use solutions with Ca concentration in the range 0.002+-04~ and K/dCa ratio in the range o to 0.05 dM.Simplifications. The full procedure, and the calculations which follow, are more complicated than the routine analyses commonly used...

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THE pH OF STRONGLY ACID SOILS

Abstract: With strongly acid soils pH-|pCa, pMg-pCa and pH-fp(CafMg) rvere unaffected bv the soil/water ratio. The amount of CaClz added to the suspensions had an effect on pH-]pCa and pMg-pCa but the effect was such that pH-!p(Ca*NIg) was independent of the salt concentration.

Cited by 5 publications

References 4 publications

A second species of polynuclear hydroxyaluminum cation, its formation and some of its properties

A second species of polynuclear hydroxyaluminum cation, its formation and some of its properties

Studies on Soil Potassium

SOURCES OF ERROR IN THE DETERMINATION OF SOIL POTASSIUM ACTIVITY RATIOS BY THE Q/I PROCEDURE

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