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Effect of liming on basic exchangeable cations of soil

Armi Kaila
University of Helsinki, Department of Agricultural Chemistry

Abstract. The effect of liming on the basic exchangeable cations in a sand, a heavy
clay and a muddy clay soil was studied with a 9 month’s incubation experiment under
laboratory conditions. Besides, observations were made in connection with some other
incubation and field experiments.

It was found that application of CaC0 3 in amounts which reduced the acidity to
about pH 7. decreased the content of exchangeable Mg in all experiments, and even a
lower application effectively prevented any net release of nonexchangeable Mg which
occurred in the muddy clay samples incubated without lime. Some fixation of K was
also usually detected, but liming increased the amount of exchangeable Na.

Essential differences apparently exist between the mechanisms of the retention of
Mg and K induced by liming: Significantly lower amounts of Mg was extracted by 0.5
HCI from the limed samples of the heavy clay and muddy clay soil than from the original
ones, while the contrary was true with K.

The mechanisms connected with the Mg fixation were discussed. Attention was paid
to the possibility that the usually poor Mg supporting ability of Finnish muddy clay
soils may be partly connected with the heavy liming necessary for the cultivation of
these acid soils.

The decrease in soil acidity as a result of liming is likely to increase the
effective cation exchange capacity of the soil and also to exert some effect on
the exchangeability of the basic cations. Fixation of some cations in non-
exchangeable forms may occur, but also release of cations from organic matter
or minerals is possible, particularly, during prolonged periods. In the field,
losses of cations by leaching or uptake of cations by plant roots will complicate
the processes.

In the present paper the effect of application of calcium carbonate on the
basic exchangeable cations of three mineral soils is studied on the basis of an
incubation experiment under laboratory conditions. Besides, results of some
laboratory and field experiments are examined from this point of view.

Experimental

Samples of a sand soil, a heavy clay soil and a muddy clay or gyttja clay
soil were collected from virgin land of the university farm in Helsinki. The

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168

samples were air-dried and ground to pass 2 mm sieve. 5 kg samples of the
sand and heavy clay soils and 4 kg samples of the muddy clay soil were incubated
in Mitscherlich pots at about field capacity and at room temperature (19 24° C)
for nine months. All three soils were incubated without any application and
with CaC0 3 corresponding to 7.5 me/100 g of dry soil. To the muddy clay,
CaC0 3 was also added in amounts of 15, 22.5, 30, or 60 me/100 g. All treatments
were in triplicates. At the end of the experimental period the samples were
air-dried and passed through a 2 mm sieve.

The exchangeable cations were extracted by washing 5 g of soil with four
50 ml-portions of several buffered or unbuffered one normal salt solutions;

NH 4OAc at pH 7. 0.9 N CaOAc + 0.1 N CaCl2 at pH 7, NH.CI, KCI and CaCl2 .

Acid-soluble Ca, Mg, K, and Na were extracted with 0.5 N HCI by shaking
for one hour in the ratio of 1 part of soil to 20 parts of the solution. Ca and
Mg in the extracts were measured by a Perkin Elmer atomic absorption
spectrophotometer 290, K and Na by an EEL-flame photometer.

Table 1. Soil samples

Sand Heavy clay Muddy clay

Sampling depth cm 0— 30 o—4o 0 100
Org. C % 2.89 0.67 2.94
Particle size fractions %

< 2 ,um 14 78 59
2- 20 /im 6 14 28

20- 200 yum 24 7 11
200-2000 /<m 56 1 2

Soil pH 6.05.7 3.5
Acidity me/100 g

N KCI 0.20.4 11.0
N NH4OAc at pH 7 5.88.5 27.5

The results were treated by Duncan’s new multiple range test. (Duncan
1955).

The soils are characterized by data in Table 1. Soil pH was measured in
a 0.01 M CaCl2 suspension in the ratio of 1 to 2.5. Soil acidity was titrated in
connection with the determination of the exchangeable cations with N KCI
and N NH 4OAc at pH 7.

The heavy clay sample is poor in organic C because of the high sampling
depth. The muddy clay sample, on the other hand, has its typical high content
of organic matter even down to the depth of one meter. The sand soil is
exceptionally rich in the clay fraction as is also the case with the muddy clay
soil. The very low pH-value of the muddy clay sample is in accordance with
its high exchange acidity which exceeds the lowest amount of CaC0 3 applied.
The exchange acidity is very low in the sand and heavy clay soils. The titra-
table acidity at pH 7 is in the former soil lower and in the latter soil only
slightly higher than the amount of lime applied in the experiment.



169

Results

The basic exchangeable cations replaced by unbuffered N NH 4 CI are recorded
in Table 2. The figures for Ca in the limed samples are in parenthesis, since
it is likely that, at least at the higher pH-values, CaC0 3 had not completely
reacted with the soil, and a part of it may only have been dissolved by NH 4CI.

In the limed samples of sand and heavy clay soils pH is 6.9, but in the muddy
clay soil only an eightfold amount of CaC0 3 was enough to keep the reaction
at about neutrality. The pH-values in this soil measured after one week of
incubation were pH 3.5, 4.1, 4.7, 5.6, 6.9, and 7.2 for the treatments with 0,
7.5, 15, 22.5, 30, and 60 me/100 g, respectively. In the following weeks the
acidity increased rapidly in samples limed with 7.5 to 22.5 me/100 g, but 30
me/100 g was able to keep the pH of the muddy clay for four weeks higher than
pH 6 and for 13 weeks higher than pH 5.

In all soils incubation with lime which kept the soil pH at about 7 distinctly
decreased the amount of Mg replaced by washing with N NH4CI. In the sand
and heavy clay soils, this decrease was about 30 %, in the muddy clay soil
only slightly lower than 50 % of the content of exchangeable Mg in the original
sample. In the highly acid muddy clay soil incubated without lime or with
7,5 me/100 g, some release of nonexchanheable Mg is apparent. This net release
was completely prevented by 15 me/100 g, and a statistically significant
decrease in the content of exchangeable Mg is detectable in sample incubated
with 30 me/100 g, which was enough to keep the soil only slightly acid for
several weeks.

Table 2. Basic exchangeable cations in soil samples replaced by N NH4CI (me/100 g)

CaCO s Soil
me/100 g pH* Ca* Mg* K* Na*

Sand
Original 6.0b 10.1a 0.47 b 0.35b 0.18a

Incubated 0 5.8a 10.0a 0.49b 0.33ab 0.18a

7.5 6.9° (15.8) 0.32a 0.30a 0.26b

Heavy clay
Original 5.7b 10.1a 8.2b 0.79a 0.44a

Incubated 0 5.6a 10.3a 8.2 b 0.85b 0.47b
7.5 6.9° (17.0) 6.0a 0.78 a 0.55 c

Muddy clay
Original 3.6b 4.9a 3.6 C 0.92 d 0.85a

Incubated 0 3.5 a 4.2a 4.4 e 0.37a 0.85a

7.5 3.6b (12.9) 4.0 d 0.92d 1.01b

15 3.8° (21.0) 3.6 C 1.09e 1.04b

22.5 4.3 d (25.5) 3.4bc 0.98 d 1.14°
30 4.9e (34.4) 3.2b 0,82° 1.16°
60 7.1 f (57.1) 1.9a 0.62b 1.44d

* Means in each column of the respective soils do not differ at P = 0.01 when they are
followed by a common letter.



170

In the sand and heavy clay soils, liming at least prevented any release of
nonexchangeable K. In the muddy clay soil, the highest amount of lime
brought about a relatively high net fixation of K: one third of the exchangeable
K in the original sample seems to be fixed. Some decrease in the exchangeable
K is obvious also in the muddy clay soil incubated with 30 me CaC0 3.

Incubation without lime slightly increased the amount of exchangeable K
in the heavy clay soil, no statistically significant effect can be found in the
low values of the sand soil, but in the muddy clay soil a very marked decrease
in the exchangeable K occurred. This somewhat surprising result which may
be partly connected with the accumulation of NH 4

+-ions in this soil, will be
studied more thoroughly in an other work.

In all soils, the amount of exchangeable Na is increased by liming, but
not at all, or only slightly, by the somewhat higher acidity produced during
incubation without lime.

Washing with the other buffered or unbuffered solutions gave results which,
in respect of the basic exchangeable cations which could be determined, did
not markedly differ from those obtained by N NH 4CI. At least, the mutual
sequence of the respective cations in the differently treated samples was equal.
In all soils, incubation with lime decreased the amount of exchangeable Mg and
increased that of Na, while the effect on exchangeable K was more complicated
but similar to that reported in Table 2. Therefore, these data are not separately
recorded in this connection.

Extraction with 0.5 N HCI was employed in order to get some more informa-
tion about the effect of liming on the release or fixation of Mg, K, and Na.
Results in Table 3 indicate that these acid soluble quantities are higher than
the corresponding amounts of exchangeable form, though those of Na in sand
and muddy clay soils are not much higher. CaC03 applied is fairly well recovered
by this extraction.

Acid soluble Mg is in the samples incubated with lime significantly lower
than in the unlimedsamples. In the heavy clay and muddy clay soils, differences
in the acid soluble Mg between the original samples and the variously treated
incubated samples are mainly of tbe same size as the corresponding differences
in the exchangeable Mg. This may be taken to indicate that fixation of Mg
induced by application of CaC0 3 , to a large part occurred as compounds or
complexes which are not readily dissolved by acid.

On the other hand, K retained unexchangeable in the samples limed to a
high pH-value seems to be quite readily soluble in 0.5 N HCI, or at least K in
the limed samples is more easily soluble than K in the unlimed samples of the
both clay soils. In the muddy clay soil this is particularly marked, since K fixed
in the sample incubated without lime seems to be bound in acid-insoluble forms.
Apparently, there are different mechanisms not only between the lime induced
fixation of Mg and K, but also between the retention of K in unexchangeable
position in the limed and unlimed samples of the muddy clay soil.

The positive effect of liming on the acid soluble Na is equal to its effect
on the exchangeable Na in the sand and muddy clay soil. In the heavy clay
soil, the tendency towards the same direction is not statistically signi-
ficant.



171

Table 3. Ca, Mg, K, and Na extracted by 0.5 N HCI at room temperature (me/100 g)

CaC0 3
me/100 g Ca* Mg* K* Na*

Sand
Original 14.0® 0.93® 0.55® 0.22®
Incubated 0 14.5® 1.00b 0.55® 0.21®

7.5 21.8b 0,90® 0.55® 0.27b

Heavy clay
Original 13.9® 18.0b 1.86® 0.75®
Incubated 0 13.2® 18.3b 2.33b 0.85b

7.5 20.8b 16.8® 2.54® 0.89b

Muddy clay
Original 6.9® 7.0® 1,34® 0.95®
Incubated 0 6.3® 6.9 d 0.71® 0.95®

7.5 14.3b 6.3® 1.26b 1.06b

15 22.3° 5.5 b 1.42d 1.13®
37. lb 5.4 b 1.58® 1.25d30

60 66,6 e 5.0 a 1.58® 1.62®5.0a

* Means in each column of the respective soils do not differ at P = 0.01 When they are
followed by a common letter.

Other observations

Results obtained in connection of some other incubation and field exper-
iments largely corroborated that heavy liming of an acid soil is likely to decrease
the amount of exchangeable Mg and often also to some extent that of exchange-
able K, while the content of exchangeable Na tends to increase with liming.

In a field trial on a clay loam soil of pH 5.4, liming in the spring with 14 000
kg CaCO;

, per hectar, until autumn decreased the acidity to pH 6.8. In samples
collected in autumn or after 3 months from the fallow plots, the content of
exchangeable Mg in the unlimed samples was 0.89 me/100 g, in the limed ones
0.57 me/100 g. The corresponding figures for exchangeable K were 0.23 and
0.18 me/100 g, respectively, and those for exchangeable Na 0.20 and 0.33 me/
100 g. The respective differences were statistically highly significant.

In an incubation experiment under laboratory conditions with three acid
muddy clay soils sampled both from the surface layer and from the depth of
40 to 60 cm, incubation for 6 months with 0, 0.5, 1.0, and 2.0 % CaC0 3 resulted
in average pH-values of 3.9, 5.1, 5.9, and 6.8, respectively. The content of
exchangeable Mg was at the lowest rate of liming about 85 %, at the second
rate about 70 %, and at the highest rate of liming about 50 % of the content of
exchangeable Mg in the samples incubated without lime. The corresponding
decrease in the exchangeable K was less regular, but in some samples the
increase in the exchageable Na with liming was quite distinct.

There was an incubation experiment on nine loam and silt soils in which
besides the effect of both liming and an application of KCI, also the effect of



172

alternate freezing and thawing on the exchangeable Mg could be studied. It
was found that treatment with 0.5 % CaC0 3 again distinctly decreased the
amount of exchangeable Mg: the drop varied from 20 to 50 % of Mg in the
samples incubated for three months without liming. No difference in exchange-
able Mg was detectable as a result of the presence of KCI in an amount of 2.5
me/100 g of soil, neither did the alternate freezing or thawing bring about
any net changes in Mg.

Discussion

In all these experiments, heavy liming markedly decreased the amount
of Mg which could be exchanged by various methods, and often also the content
of exchangeable K was lowered. Since losses by leaching were excluded in the
incubation experiments, fixation, or at least some kind of reduction in the
exchangeability of these cations apparently occurred.

Liming has been found to increase fixation of K (Keränen 1946, Wiklan-
der 1954, Kaila 1965 etc.). This is most likely connected with release of
aluminium hydroxide polymers from the interlayer position of clay minerals by
the increase in soil pH, but also other mechanisms may be involved.

Though fixation of K has been the subject of numerous papers, rather
little is reported about the fixation of Mg. Studies on the effect of liming on
Mg usually treat the equilibrium between Mg in the soil solution and Mg sorbed
as an exchangeable cation.

Wiklander and Koutler-Andersson (1959) found that in a 30 years’
field trial liming with 12 000 kg/ha of CaC0 3 decreased the content of exchange-
able Mg from 2.7 me/100 g in the unlimed plots to 2.2 me/100 g. They supposed
this to be connected with losses of Mg by a higher leaching rate from the limed
plots. On the other hand, they reported that air-drying of the soil samples
decreased the exchangeable Mg in the limed plots by about 8 % of that in the
undried samples from the surface layers down to the depth of 35 cm; in the
samples from the unlimed plots the effect of drying was detectable first in
deeper layers. The authors refer to a previous work (Malquori and Wiklan-
der 1950) which proved that both aluminium and iron silicates fixed K and
particularly Mg in nonexchangeable form, probably as insoluble K- and Mg-
silicates. In addition to the formation of Mg-silicates, Mg-Al-silicates, or Mg-
Fe-silicates, also binding into the mineral structure is suggested as possible
mechanism for this fixation brought about by drying of soil samples.

Also Eaton et ai. (1968) showed that MgSi0 4 precipitates in soils at high
pH. Hunsakek and Pratt (1970), on the other hand, demonstrated the forma-
tion of mixed Mg-Al-hydroxides in soils when raised to alkaline pH-levels.
Doner (1967, ref. Hunsaker and Pratt 1970) confirmed the inclusion of Mg
in CaC0 3 as it precipitated. McLean and Carbonell (1972) again, suggested
that conversion of Mg to nonexchangeable forms as a result of liming of a silt
soil to pH 6.8 may have been primarily by chelation via organic components
or by precipitation as oxalates, fatty acids or phosphates rather than by precip-
itation as silicates or aluminosilicates.



173

It is difficult to see which of these mechanisms was responsible for the
fixation of Mg in the soils of the present study. The samples were air-dried
before analysing, and it probably intensified the retention of Mg. In any case,
the combined effect of incubation, liming and air-drying bound Mg as com-
pounds or complexes which were not readily soluble in 0.5 N HCI, contrary
to K fixed under the same conditions. Further studies are needed to ascertain
the nature and importance of Mg fixation induced by liming.

It is of interest to note that in an experiment carried out by Wiklander
and Koutler-Andersson (1963), the amount of Mg transferred from non-
exchangeable to exchangeable form during one year’s storage was rather low
in soil samples saturated with Ca-ions as compared to samples saturated with
H-ions. Release of nonexchangeable Na tended to be slightly higher in samples
saturated with Ca-ions than in those saturated with H-ions, but the contrary
seemed to be true with changes in K. The present results do not disagree with
these data, if differences in the treatments are taken into account.

In a previous work (Kaila and Kettunen 1973), it was found that while
some slight release of nonexchangeable Mg was detectable in most soils applied
to exhaustive cultivation in greenhouse, the muddy clay soil which was the
only sample treated with lime, did not show any net release of nonexchange-
able Mg. It is likely that one reason for the rather low amounts of plant-available
Mg in the Finnish muddy clay soils is the effect of the fairly heavy liming
which is usually needed for profitable cultivation of these acid soils.

REFERENCES:

Duncan, D. B. 1955. Multiple range and multiple F tests. Biometrics 11: 1 42.
Eaton, F. M., McLean, G. W., Bredell, G. S. & Doner, H. E. 1968. Significance of silica

in the loss of magnesium in irrigation waters. Soil Sci. 105: 260 280.
Hunsaker, V. E. & Pratt, P. E. 1970. The formation of mixed magnesium-aluminum

hydroxides in soil materials. Soil Sei. Soc. Amer. Proc. 34: 813 815.
Kaila, A. 1965. Fixation of potassium by soil samples under various conditions. J. Scient.

Agric. Soc. Finl. 37: 195 206.
—» & Kettunen, H. 1973. Magnesium-supplying power of some Finnish mineral soils.

J. Scient. Agric. Soc. Finl. 45: 319—324.
Keränen, T. 1946. Kaliumista Suomen maalajeissa. Summary: On potassium in Finnish

soils. Acta Agr. Fenn. 63.
Malquori, A & Wiklander, L. 1950. Influence of alternate wetting and drying on potassium

and magnesium fixation and base exchange capacity of synthetic aluminium and iron
silicates. IV Int. Cong. Soil Sci. Trans. I: 141 —l5l.

McLean, E. O. & Carbonell, M. D. 1972. Calcium, magnesium, and potassium saturation
ratios in two soils and their effects upon yields and nutrient contents of German millet
and alfalfa. Soil Sei. Soc. Amer. Proc. 36: 927—930.

Wiklander, L. 1954. Forms of potassium in the soil. Rep. Potassium Symposium 1954,
Berne: 109-121.

—» & Koutler Andersson, E. 1959. Kalkens markeffekt 111. Grundförb. 12:1 40.
» & Koutler-Andersson, E. 1963. Influence of exchangeable ions on release of mineral-

bound ions. Soil Sci. 95:9 15.



174

Selostus

Kalkituksen vaikutus maan emäksisiin vaihtuviin kationeihin

Armi Kaila
Yliopiston maanviljelyskemian laitos, Viikki

Kalkituksen vaikutusta hiekkamaan, aitosaven ja liejusaven emäksisiin vaihtuviin katio-
neihin tutkittiin 9 kk:n muhituskokeessa laboratorion olosuhteissa. Lisäksi tarkasteltiin eräit-
ten muitten muhitus- ja kenttäkokeitten analyysitietoja.

Todettiin, että CaCQ 3 annettuna määrinä, jotka nostivat maan reaktioltaan suunnilleen
neutraaliksi, alensi kaikissa kokeissa merkittävästi vaihtuvan Mg:n pitoisuutta. Heikompikin
kalkitus näytti estävän liejusaven vaihtumattoman Mg:n nettomobilisoitumisen, jota oli havait-
tavissa, kun maata muhitettiin ilman kalkitusta. Useimmissa maissa oli havaittavissa myös
K:n pidättymistä kalkituksen tuloksena, mutta vaihtuva Na yleensä lisääntyi kalkituksen
myötä.

Kalkituksen aikaansaama K:n ja Mg:n pidättyminen oli mekanismiltaan erilaista: ainakin ai-
tosavi- ja liejusavinäytteistä 0.5 n HCI uutti kalkituista ja muhitetuista maista merkittävästi
■vähemmän Mg kuin alkuperäisistä, mutta K:n kohdalta tulos oli päinvastainen.

Tulosten tarkastelussa käsiteltiin Mg:n pidätyksen mekanismia kirjallisuuden melko niuk-
kojen olettamusten perusteella. Esitettiin, että mahdollisesti eräänä syynä liejusaviemme
yleensä heikohkoon Mg-tilaan saattaa olla näiden maiden tavallisesti vaatima verraten voima-
kas kalkitus, joka voi johtaa Mg:n pidättymiseen vaihtumattomaksi.