T H E EXTRACTABLE MANGANESE OF SOIL E. R. PAGE*

(West of Scotland Agrinrltural College, Auchinm’ve, Ayr)

Summary Exchangeable manganese extracted from soil with calcium nitrate solutions

shows some increase as the period of extraction is prolonged. For a given time of extraction the exchangeable manganese of soil behaves as a typical divalent cation obeying simple exchange theory, contrary to a previous report in the litera- ture. Soil particles discriminate between calcium and manganese ions, calcium ions being held more firmly.

Introduction MANGANESE exists in soil in a wide variety of forms. There are several ionic species, and many com ounds, some of which, like so-called ‘maneanese dioxide’, may exhifit more than one crystalline form. The chemistry of the Mn compounds of the soil has not yet been fully elucidated, and so far no satisfactory method of fractionation of sod manganese has been devised to allow characterization of the different forms, although several empirical schemes exist of which the most widely used are those of Leeper (1935) and Sherman et al. (1942).

A lar e part, perhaps most, of the Mn is in the form of various oxides.

into solution by reduction or through complex formation by root exudates or both. Insoluble organic complexes exist, which are robably

the pA relationship (Page, 1962). Some of these organic complexes may be of bacterial or fungal origin; the presence of micro-organisms and their metabolites complicates the picture.

The general consensus of opinion is that plants take u divalent Mn

Weir and Miller, 1962) although there is also the possibility that solu le anionic complexes of Mn are available to them (Heintze, 1957). If attention is directed exclusively to the divalent form one would expect it to behave in soil in ions such as calcium, although these others will greater uantities. Some doubt that Mn of Boken (1958).

These B orm a reserve, and although relatively insoluble may be brought

main1 responsible for non-availability of Mn to plants, as is s R own by

t from the soil solution (Leeper, 1947; Fujimoto and S K erman, 19 8;

way was cast by B t e results

negative logarithm of the s ecific electrical conductivity, see W i ittles

E q e r i m t a l Materials and Methods Soil A (a loam) was air-dried, passed through a 2-mm sieve and

thoroughly mixed. After shaking 30 g soil with 75 ml distilled water for I hour, the pH of the suspension was 4-51 and the pC was 3.1 (the

and Schofield-Palmer, 19517. The total Mn content was 210 ppm. A second Scottish loam B was used for some experiments. Water pH and

I Present address : National Vegetable Research Station, Wellesbourne, Warwick. Journal of Sol1 Science. Vol. 15, No. 1, 1964

94 E. R. PAGE pC obtained as above were 5.06 and 05 respectively and total Mn content was 440 ppm. A Danish soil 8 was kindly supplied b Miss Boken. pH measurements were made using a Cambridge Porta l le pH meter with a glass electrode. pC was obtained from measurements with a dip-type conductivit cell (Mullard E 7591 /B) connected to a sensitive

at a fre uency of 1600 C.P.S. Cation exchange capacity of soils was

Calcium nitrate solutions were prepared from A.R. HNO, and A. . CaCO,. After boiling for one hour and standing overnight excess CaCO, was filtered off. Concentration of solutions was checked by EDTA titration. pH values of these solutions were within the range 6.3 to 7- . Extraction of soil with Ca NO,), was b the method of Heintze (19383.

Unless otherwise specified the time of shaking was 2 hours. Extracts were filtered through Whatman No. 42 papers.

Man anese determination. Where possible the periodate oxidation

to avoid recipitation of CaSO,. With smaller amounts of Mn the

The authors reported that both Ca and NO, interfere. This seems likely to be the result of Mn contamination of most commercially available Ca and NO, sources; in any case the interference was overcome by adding Ca(N0, , from the same source to the standards employed in

determinations were made in solutions of 0.5 M Ca(NO,),. Total Mn was determined by the method of Page et al. ( I 962).

Results Duration of extraction. 20 g of soil A was extracted with 200 ml 2N

Ca(N03k. The combined results of two experiments are shown in Fig. I. A slig t increase in extractable Mn was evident in 6 hours; about 7 per

cent more than after 0.5 hour extraction. Boken (1958) found much greater increases during this period, from 29 per cent to 76 per cent for different soils, the increase continuing, though at a decreasing rate, during the whole 24-hour period of investigation. A similar increase in extractable Mn occurs on storage of soil (Boken, 1952; Zende 1954) and soil A had already been in storage in the air dry condition for more than a year. Hamnes and Berger (1960) have shown that the Mn released on air d ing comes from organic soil Mn. It is likely that both increases

rapidly under the influence of an extracting solution. Zende (1954) noted that the increase was correlated with the organic matter content of the soil investigated. Evidently the soil contains labile organic complexes of Mn which break down to release exchangeable Mn. These complexes probably break down quickly when the soil is heated, and this may account for the considerable increases of extractable Mn which occur when glass-house soils are steam sterilized.

conductivity brid e i alanced by means of an oscilloscope and operated

k measure 8 by the conductivity method of Mortland and Mellor (195 ).

Weighed uantities of soi I were place 2 in glass bottles with measured volumes o 9 solution and shaken mechanically on a reciprocating shaker.

metho C f was used, with HNO, replacing the more usual H,SO, in order

methane- g ase method of Cornfield and Pollard (1950) was employed.

making the call b ration curves and to the unknown solutions so that all

are resu 7 ts of one process which goes on slowly in storage and more

THE EXTRACTABLE MANGANESE OF SOIL 95 In this experiment, as in the others reported in the aper, pH values

a characteristic pH value on the solution in contact with it. In this instance commercially available Ca(N03), was used, and the initial pH of the extracting solution was 3.60; all the extracts had pH values in the

were recorded and demonstrated clearly the ability o f t K e soil to impress

range 3- 7 to 4-00. The same soil when shaken with 2N Ca(N0, , of initial p& either 6.96 or 7-02 with a soil : solution ratio vaying i rom I : 5 to I :40 gave extracts whose final pH fell within the limits 3-95 to 4-40. In the remainder of this aper the effects of hydrogen ions are ignored. This is not because pgeffects are of no consequence; on the contrary, they are extremely important as has been shown previously in a study of the effects of pH on Mn availability (Page, 1962). The pH of the extracts of soil A in all experiments reported here varied between the limits of 4-67 to 5'70, so that a small part of the variation in extracted Mn may be accounted for by pH effects; nevertheless it is justifiable to ignore the effects of the hydrogen ions because the influence is secondary and reasonably small compared with the effects of the high concentrations of calcium ions.

Variation of wolume ratio. Volume ratios (g soil : ml extractin solu- tion) varying between I : I and I : 160 were investigated using N, 2k, and 4N solutions of Ca(NO,),. The results are shown in Table I.

The amounts of Mn found, expressed as pm of soil, were scarcely affected by change of volume ratio. With ?$ Ca(N0, , approximately 25 p m Mn was found; with 2N solution the vaues were more

28 ppm. It is unlikely that there is any significance in the difference between these two latter figures, which was within the probable experi- mental error.

varia E le, but averaged about 29 ppm; while for 4N solution it was

96 E. R. PAGE

TABLE I

Manganese (as ppm) extracted f r m soil A by solutions of calcium nitrate

Ratio g soiljml extract 5 ca1c:- ni;ate

I : 2 - 5 I I I O I I : .$ I : I O I : 2 0 I : 4 0 1:80 1:160

/ P 0 loo 200 300 400

Grams of soil in suspension in 800

FIG. 2. Effect of volume ratio on Mn extracted from soil A. 0 Extraction with N Ca(NOJ, solution. + 9 ) ss zN s y 9 )

0 9s 9 s 4N 99 ss

The figures obtained were used to calculate the total amounts of Mn in solution in the appropriate volume of extractant, and in Fig. z these are plotted against the weights of soil in suspension.

A straight line is obtained which passes through the origin of the graph, showing that the concentration of Mn in solution is proportional to the amount of soil in suspension, exact1 as would be expected if

be represented by the equation

sim le exchange occurs between soil Mn an B Ca ions from the solution, wit R the latter in overwhelming excess. The behaviour of the soil may

m M n + C a + + + I C a + M n + +

so that with excess Ca ion present the concentration of Mn ion is proportional to weight of soil in suspension.

THE EXTRACTABLE MANGANESE OF SOIL 97 The results of Boken (1958 present a striking contrast to this simple

picture. In her results the d n extracted expressed as a soil content in Ppm differs greatly de ending on the volume ratio, and when plotted in the same form as Fig. 2 give a positive intercept of considerable magnitude. Results for two soils are illustrated in Fig. 3. Most of Boken’s results obtained with Mg(NOJa as the extractant are like those

Weight of soil (g)

FIG. 3. Volume ratio effect. From results of Boken (1958). Soil No. 4. 0 Soil No. 16.

2N Ca(NOJ, extraction. ---- 2N Mg(NO,), extraction.

for soil No. 4, in that this form of plot gives a zero intercept, but all results obtained with Ca(NO,), give a positive intercept. The most likely explanation appears to be that the extracting solutions themselves con- tained Mn, so that the interce t value represents contaminating Mn.

two grounds; firstly her experiments had shown that added n was ‘absorbed’ on to the soil and could not be measured; secondly that in a articular example giving a graph intercept suggesting contamination

&y 0.047 mg Mn, analysis of the Mg(N03), solution used showed 0.015 mg Mn per 200 ml.

An ex eriment to verify ‘absorption’ of added Mn was carried out

contaminated with Mn was used; it gave results s i m h to those obtained by Boken with apparent extractable Mn figures of 88.0, 58.5, 51-3, 0.8, and 38 ppm soil corresponding to 5 , 10, 20, 40, and 80 g of soil. %.he intercept corresponds to the measured contamination which was 0.264 mg Mn per zoo ml of extractant. When Mn corresponding to 0.270 m per zoo ml Ca(NO,), solution was added and the experiment repeatel the slope of the line changed, and, although the value of the interce t

Id This was thought unlikely by I f oken (private communication, 19 8) on

with soi P B and the results are in Fig. 4; 2N Ca(NOS), known to be

increased as expected, the Mn extracted not only failed to increase f y 6113.1 H

98 E. R. PAGE the expected amount, but actually less Mn in absolute quantities was extracted from the larger quantities of soil. A separate experiment showed that this did not occur if the extra Mn was added later, after separation of the soil b filtration, but before the development of the permanganate colour. Jhese results lifted the line on the graph by the

I I 1 I I 1 I I I

0 10 20 30 40 50 60 7 0 80 Weight of soil (g)

FIG. 4. Effect of volume ratio on Mn apparently extracted from soil B when extractant was contaminated with Mn.

0 Extraction using 200 ml2N Ca(NO& contaminated with 0.264 mg Mn. 0 Extraction as above, with 0.270 mg additional Mn.

ap ropriate amount without change of slope, as would be expected.

so far as the effect of addition of Mn to the extractant reduced the ap arent extractability of soil Mn.

Eesults similar to these, which when plotted gave a positive intercept, have been obtained by Boken (private communication, I 60) even when

together with some of the Mg(NO,), used for its extraction. Analysis confirmed that the Mg(N0, a was man anese-free. But in contrast with

corresponding to 0.025 mg Mn, the results obtained here gave a zero interce t. These results and those obtained b adding 0.060 mg Mn per

intercept of the expected size was found and the slope of the line was decreased.

Bo R en’s observation that absorption of Mn takes place was confirmed in

the extractant contains no Mn. Soil D was supplied B y Miss Boken

Boken’s results for this soi r‘ , which w en plotted showed an intercept

200 m P of extractant are shown in Fig. 5. k here Mn was added an

THE EXTRACTABLE MANGANESE OF SOIL Boken's results can probably be explained by Mn contamination

introduced with the extractant, or perhaps at some later stage before the separation of the soil by filtration. There ap ears to be some evidence in the published results (Boken, 1958) to in a icate that development of permanganate colour with ammonium persulphate may be incomplete

99

i

0 10 20 30 40 50 60 70 80 Welght of soil (g)

FIG. 5. Volume ratio effect. Soil D (Copenhagen). 0 Extraction using 200 ml 2N Mg(NO,),. 0 Extraction as above, with 0.060 mg added Mn. + Results obtained by E. Boken.

when ratios of soil to extractant are high, particular1 with peaty soils, and this may account for the correlation found by her g etween C content of soils and the variation of extractable Mn found to result from different volume ratios of extraction.

It is considered that published results to ether with those presented

is adequate to explam the behaviour of extractable Mn in soi s. theor Resu ts seemingly casting doubt on the adequacy of the theory are capable of an alternative explanation.

Vanktion of extractant concentration. Ca(NO,), solutions of various concentrations between 4N and N/2048 were used to obtain extractable Mn of soil A, and a water extract was also made. In these experiments a volume ratio of 10 g soil to 200 ml Ca(NO,), solution was used. Wide variations in concentration of extractant had practical1 no effect on the amount of extracted Mn until a critical level was reac K ed. The level of extractable Mn was lower when solutions of calcium nitrate of N/64 or less concentrated were used.

In Fig. 6 extractable Mn, as ppm of soil, is plotted against the pC of the extract, and the pC of extract and extractant are plotted against pN

P here provide no evidence against the view t a at the simple ion exchan e

I00 E. R. PAGE (the negative logarithm of the normality) of the extractant. Fig. 6 shows that the level of extractable Mn begins to fall only when the concentration of the extract (as shown by its conductivity) was greater than the con- centration of the extractant. Below an extractant concentration of N/64, represented as pN 1.806 or more, the pC of the extract fell increasingly

3

2

PN

I

(

\ 01

\

t \ \ \ \ 0

/" s"

1

4 DC

I 2

FIG. 6. Effect of variation of concentration of Ca(NO,), extractant. 0 Mn extracted from soil A, plotted against pC of extract (6-4

0 pN of extractant, plotted against pC of extractant. + pN of extractant, plotted against pC of extract.

ppm Mn in water extract).

below that of the extractant, re resenting an increase in concentration.

With an extracting solution of N/16 (pN = 1.204) the pC of the extract was slightly greater than that of the extractant, showing that the soil had gained ions from the solution, and similarly for all more concentrated solutions. Under these circumstances the maximum amount of Mn appeared in the extract. From the figure it may be estimated that approximately at pN 1-5 (or 0.0316 N) the conductivity of the extract

In this range the soil was yiel g. mg up ions to the extracting solution.

THE EXTRACTABLE MANGANESE OF SOIL I 0 1

would be equal to that of the extractant. This represents the equilibrium oint at which gains and losses of cations to and from the electric double

Payer enveloping each soil particle were equal. The c.e.c. of this soil was 0.234 me/g, so that the total exchangeable

Mn, calculated from the maximum figure of 28 ppm as 1-02 pe/g represented about I in 230 of the total counter ions on a chemical equiva- lent basis. This, of course, represents only a small fraction of the 210

pm of total soil Mn. The remaining 85 per cent would be present as

$he approximate concentration of ions in the water extract could be calculated from the pC. The pC of -877 would correspond to a Ca NO,),

her oxides, insoluble organic complexes, or other forms.

concentration (this may be read o s the pC/pN curve of Fig. 6) o I about N/~ooo (pN = of the cationic conductivity of the water extract

ions, and in any case other divalent ions (Richards, 195 ) and the fact that the anions 4 would not be NO, ions would not reat alter the situation. In the

water extract 6-4 ppm Mn were foun$ so tzat on the basis of e uivalents about I in 4 of the ions given up by the soil to the water were d n ions.

Thus the exchangeable Mn ions of this soil are released more readily than Ca, as mi ht be ex ected; no figures are available for soils, but Kitchener (1957f reportecfthe lyotropic series Mn++ < Mg++ < Zn++ < Cu++ < Ni++ < Co++ < Ca++ for an ion exchange resin, and the series for soils are probably similar. This evidence should not be taken to mean that divalent Mn ions always assume this relationship towards Ca ions. The specificity of exchangers towards different species of ions may alter depending on the anionic field strengths of the exchangers, as has been demonstrated for monovalent cations by Eisenman (1962).

The evidence resented in this paper suggests that exchan eable Mn

typical divalent ion, and should o ey the laws governing Donnan equilibria, provided that selectivity effects are taken into account.

a E in the soil, whic R constitutes only a art of the total Mn, be aves as a

Acknowledgements This work was begun at the suggestion of Dr. A. J. McGregor and Mr.

E. K. Schofield-Palmer, and the results were incorporated in the author’s Ph.D. thesis (University of Glasgow, 1961). Thanks are expressed for the kind co-o eration of Miss Else Boken, Royal Veterinary and Agricultural College, &penhagen, in supplying results and materials.

REFERENCES BOKEN, E. 1952. On the effect of storage and temperature on the exchangeable

manganese in soil samples. Plant and Soil. 4, 154-63. - 1958. Investigations on the determination of the available manganese content of soils. Ibid. 9,269-85.

CORNFIELD, A. H., and POLLARD, A. G. 1950. Use of tetramethyldiaminodiphenyl- methane for the determination of small amounts of manganese in plant materials and soil extracts. J. Sci. Fd Agric. 1, 107-9.

EISENMAN, G. 1962. Cation selective glass electrodes and their mode of operation. Biophys. J. 2, 259-323.

I02 E. R. PAGE FUJIMOTO, C. K., and SHERMAN, G. D. 1948. Behaviour of manganese in the soil and

the manganese cycle. Soil Sci. 66, 131-45. HAMNES, J. K., and BERGER, K. C. 1960. Chemical extraction and crop removal of

manganese from air-dried and moist soils. Soil Sci. SOC. h e r . Proc. 24, 361-4. HEINTZE, S. G. 1938. Readily soluble manganese of soils and marsh spot of peas.

J. agric. Sci. 28, 175-86. - 1957. Studies on soil manganese. J. Soil Sci. 8, 287-300. KITCHENER, J. A. 1957. Ion-exchange Resins. Methuen, London. LEEPER, G. W. 1935. Manganese deficiency of cereals: plot experiments and a new

- 1947. The forms and reactions of manganese in the soil. Soil Sci. 63,79-94. MORTLAND, M. M., and MELLOR, J. L. 1954. Conductometric titration of soils for

cation-exchange capacity. Soil Sci. SOC. Amer. Proc. 18, 363-4. PAGE, E. R., SCHOFIELD-PALMER, E. K., and MCGREGOR, A. J. 1962. Studies in soil

and plant manganese. I. Manganese in soil and its uptake by oats. Plant and Soil.

- 1962. Studies in soil and plant manganese. 11. The relationship of soil pH to

RICHARDS, L. A. (ed.) 1954. Diagnosis and Improvements of Saline and Alkali

SHERMAN, G. D., MCHARGUE, J. S., and HODGKISS, W. S. 1942. Determination of

WEIR, C. C., and MILLER, M. H. 1962. The manganese cycle in soil. I. Isotopic ex-

WHITTLES, C. L., and SCHOFIELD-PALMER, E. K. 1951. On pC, pS, and pN as

ZENDE, G. K. 1954. The effect of air-drying on the level of extractable manganese in

hypothesis. Proc. Roy. SOC. Vict. 47, N.S. 225-61.

16, 238-46.

manganese availability. Plant and Soil 16, 247-57.

Soils. Agric. Handbook No. 60, U.S.D.A.

active manganese in soil. Soil Sci. 54, 253-7.

change reactions of 5 4 M n in an alkaline soil. Canad. J. Soil Sci. 42, 105-14.

indicating functions of electrical soil conductivity. J. Soil Sci. 2, 243-5.

the soil. J. Indian SOC. Soil Sci. 2, 55-61.

(Receiwed 9 May 1963)