JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND
Maataloustieteellinen Aikakauskirja

Voi. 58: 43—46, 1986

RESEARCH NOTE

Base-neutralizing capacity of Finnish mineral soils

HELINÄ HARTIKAINEN
Department of Agricultural Chemistry, University of Helsinki,
SF-00710 HELSINKI, Finland

Abstract. The base-neutralizing capacity, BMC, (OH- as meq kg -1 needed to raise soil
pH to 7), was determined graphically from curves obtained in KOH titration (at a constant
ionic strength of I = 0.1). In 84 soil samples, BMC, amounted to 0—316 meq kg-1

, being
highest in the heavy clay soils and lowest in the non-clay soils. In different textural groups,
BMC, seemed most markedly to be dependent on the initial soil pH, followed by organic C
or oxalate soluble Al, in the coarser clays also on clay content. The results evidence that in
determination of lime requirement, attention should be paid to the capacity of soil acidity.
In routine soil testing, detailed lime recommendations for various soil types are needed.

Index words: base-neutralizing capacity, soil acidity, titration, pH-buffering, lime requirement, soil testing

Introduction

Since Kamprath (1970) proposed the ex-
changeable A 1 as a criterion for liming, vari-
ous lime recommendations have been dis-
cussed widely. Some of them are based on the
amount of base required to bring a soil to a
given pH and others on that needed to in-
activate toxic substances. In Finnish soils Al,
not only as monomeric trivalent ion but prob-
ably to a much greater extent as polymeric
hydroxy-Al, increases the amounts of lime
needed to amend the acidity (Kaila 1971).
However, in routine soil testing the liming
recommendations are based on pH ( „ 20) and
NH 4-acetate (pH 4.65) extractable Ca. Män-
tylahti and Yläranta (1980) have found

this method rather unsatisfactory especially
for mineral soils where it overestimates the
requirement. They proposed a titrimetric
method for a more precise determination. The
purpose of the present study was to estimate
the base-neutralizing capacity of Finnish min-
eral soils in various textural groups. The soil
factors accounting for its variation were in-
vestigated statistically.

Material and methods

The material consisted of 15 heavy clay
soils (60 % or more clay fraction <2 /*m),
41 coarser clay soils (30—59 % clay), 20 silt
soils (main fraction 2—20 /mi) and 8 fine sand

43

https://www.c-info.fi/en/info/?token=E53B11RL-6h_UJDW.p6kzt0ixw_xsAVVhODIz2w.yuCP_GdO1bXN3Oo3P-OhW5ye_GCf7c0vFuUU-ddlJfZ9mt1jdhk6KosSnnCh5froT9bUQLe41zQbocwmo4vwIQ_ZKzafsjDYIQWJg8tsQLgp7XV-I2qmnzMLRkOrTDTUZmjifP5LXdRlYjWYudNwEW0Cdt4QyWX3XZFLaUBaiYlzr_CgCg


soils (main fraction 20—200 /an). The ana- y = 10.70 Corg + 0.50 Al0 90.34 pH +

lytical methods and soil characteristics are
reported in a previous paper (Hartikainen
1985).

The method of batch base-titration and its
precision are presented in detail elsewhere
(Hartikainen 1986). In brief, 5 g of soil was
treated in duplicate with 50 ml of solutions
containing 0, 0.3, 0.6, 0.9, 1.2, or 1.5 meq
base (KOH) at an ionic strength of I = 0.1
(adjusted by KCI), equilibrated for 4 d (stirred
once). Thereafter pH was measured with an
analogous pH-meter, using a separate refer-
ence electrode. The base-neutralizing capacity
(BNC) was determined graphically from the
titration curves and expressed as a quantity of
base (meq kg-1) needed to elevate the soil pH
to 7.

Results and discussion

In 84 samples BNC, ranged from 0 to 316
meq kg-1

, the average and median being 107
and 95 meq kg-1

, respectively. As expected,
it tended to increase with decreasing soil pH,
the correlation of log BNC 7 vs. pHCaC ,2 being
r = —o.B4*** (n = 0.83). In the three textural
classes BNC, was markedly higher in the
heavy clay soils than in other soil groups. The
mean values with 95 % confidence limits and
ranges were as follows:

BNC, range
Heavy clays (n= 15) 164.8 +44.8 68—316
Coarser clays (n =41) 101.9+16.2 16—232
Non-clay soils (n=28) 82.2±20.4 0—212

In all samples, BNC7 correlated closely
also with NH 4-acetate and NH4-oxalate solu-
ble A 1 (r = o.Bs*** and o.77***, respectively),
followed by organic C (r = o.72***) and clay
content (r= o.so***). When its dependence on
soil characteristics was investigated by the
regression analysis, the statistically significant
variables were: organic C (Corg ,

%), oxalate
soluble A 1 (Al o, mmol kg-1), soil pHCao2 ,

and clay content (clay, %).

In the heavy clays the relationship between
BNC7 (y) and soil characteristics conformed
to the equation:

519.27

The coefficient of multiple determination
R 2 was o.93*** and the standard error of
estimate S was 23.77.

In the coarser clays, also the clay content
was included in the equation:

y = 6.31 Corg , + 0.74 Al0 + 0.90 clay
54.56 pH + 276.56
R 2 = o.9l***, S = 16.44

In the non-clay soils the equation was:

y = 9.21 C org . + 0.31 Al0 54.43 pH +

311.74
R 2 = o.9l***, S = 16.87

The relative importance of various variables
affecting the BNC, values may be compared
on the basis of the /3-coefficients:

pH Corg Al0 clay
Heavy clays —0.52 0.31 0.31
Coarser clays —0.61 0.23 0.29 0.15
Non-clay soils —0.68 0.30 0.19

BNC, seems to depend most markedly on
soil pH CaCl2, followed by organic C in the
non-clay soils and by oxalate soluble A 1 in the
coarser clay soils. In the heavy clay soils these
variables appear to be equally important. The
results show a similar trend as reported in an
earlier study of Kaila (1971) where the rela-
tive importance of oxalate soluble A 1 ex-
plaining the variation in titratable non-ex-
changeable acidity was in the clay soils greater
than that of organic C, but in the other min-
eral soils it was less important. The soils
being classified according to their clay content
reduced the range and, thus, the importance
of clay in various groups.

The differential base-buffer values (OH-
as meq kg-1 needed to raise soil pH sequen-
tially by 0.5 units) and their dependence
on soil properties have been studied earlier
(Hartikainen 1986). In soils of various pH
ranges the soil characteristics explaining the
variation in base-buffer values varied marked-
ly: oxalate soluble Fe, various fractions of
A 1 (exchangeable, non-exchangeable acidic

44



and oxalate soluble Al), clay content and
organic C. The clay content was of signifi-
cance only in the strongly acid soils (pH ZPX

4.8) where its role in base-buffering in the
beginning of titration was concluded to be due
to H + ions on the permanent charges of min-
erals. As the exchange of H + ions from per-
manent charges is stated to constitute only
a relatively small amount of exchangeable
acidity (VEITH 1977), at least in the later
phase of the titration the role of clay was
assumed to be attributable to other buffering
mechanisms, e.g. by release of Al from the in-
terlattice space of Al-chlorites.

In principle, the BNC value stands for a
cumulative effect of factors responsible for
buffer action during a stepwise titration.
Thus, the components that contribute to BNC
depend on the reference pH chosen. Oxalate
solubleFe excluded, all factors earlier found
by Hartikainen (1986) to affect the buffer
values in various pH categories were in effect
included in the variables explaining the varia-
tion in BNC 7 in the present study.

In all textural soil groups pH, i.e. intensity
of acidity, was a decisive variable. However,
several forms of acidity account for the total
acidity of a given soil. Numerous compounds
contain undissociated H +

, and a stepwise
dissociation of H + occurs with increasing
pH. Thus, the other variables involved, even
though related to the capacity of acidity, are
indirectly connected also with the nature of
acidity. There is a close relationship between
pH and various fractions of AI (e.g. Marion
et al. 1976). Yet, soil pH is a poor measure

of Al concentration of soil solution, because
organic matter controls the relationship be-
tween pH and Al 3+ activity in acid soils
(Hoyt 1977, Bloom et al. 1979, James and
Riha 1984).

The results evidence that if the titration
method cannot be adopted in routine soil
testing, it is necessary to frame individual lime
recommendations for various textural soil
types. In the determination of lime require-
ments, attention should be paid to soil factors
related to the capacity of soil acidity.

For agricultural purposes, a reference pH
lower than 7 is, of course, more appropriate
and more realistic. It should be taken into
account that the beneficial effects of a higher
pH on microbial activity and availability of
plant nutrients are, at least to some extent,
masked by current fertilization practice. If all
essential elements are provided in adequate
quantities, lime amounts only sufficient to
eliminate toxic elements (e.g. exchangeable
or soluble Al) or to reduce their concentra-
tions to a low level are needed to obtain max-
imal yields (Kamprath 1970, Schwertmann
and Attenberger 1979, Webber et al. 1982).
Some viewpoints do, however, justify liming
over this critical pH level. Important con-
sequences of base treatment include an in-
crease in the effective charge density, resulting
in a reduction in leaching losses of essential
basic cations, as well as an increase in the acid-
neutralizing capacity of soils.

Acknowledgement. The author wishes to thank the Maj
and Tor Nessling Foundation for the grant which made
it possible to complete this study.

References

Bloom, P.R., Mcßride, M.B, and Weaver, R.M. 1979.
Aluminum organic matter in acid soils: Buffering and
solution aluminum activity. Soil Sei. Soc. Amer. J. 43:
488—493.

Hartikainen, H. 1985. Acid-neutralizing capacity of
Finnish mineral soils. J. Agric. Sci. Finl. 57: 279—283.

1986. Acid- and base-titration behaviour of Finnish
mineral soils. Z. Pflanzenern. u. Bodenkde: (in press).

Hoyt, P.B. 1977. Effects of organic matter content on

exchangeable A 1 and pH-dependent acidity of very acid
soils. Can. J. Soil Sci. 57: 221—222.

James, B.R. and Riha, S.J. 1984. Soluble aluminum in
acidified organic horizons of forest soils. Can. J. Soil
Sci. 64; 637—646.

Kaila, A. 1971. Aluminium and acidity in Finnish soils.
J. Scient. Agric. Soc. Finl. 43: 11—19.

Kamprath, E.J. 1970. Exchangeable aluminum as a
criterion for liming leached mineral soils. Soil Sci.
Amer. Proc. 34: 252—254.

Marion, G.M., Hendricks, D.M., Durr, G.R. and Ful-

45



ler, W.H. 1976. Aluminium and silica solubility in
soils. Soil Sci. 121: 76—82.

Mäntylahti, V. and Yläranta, T. 1980. The estimation
of soil lime requirement in soil testing. Ann. Agric.
Fenn. 19: 92—99.

Schwertmann, U. and Attenberoer, E. 1979. Verände-
rungen von Bodeneigenschaften durch langjährige pH-
verändernde Dungung. Landwirtsch. Forsch. 32: 119

128.
Veith, J.A. 1977. Basicity of exchangeable aluminium,

formation of gibbsite, and composition of exchange
acidity in the presence of exchangers. Soil Sci. Soc.
Amer. J. 41: 865—870.

Webber, M.D., Hoyt, P.B. and Corneau, D. 1982.
Soluble Al, exchangeable Al, base saturation and pH
in relation to barley yield on Canadian soils. Can. J.
Soil Sci. 62: 397—405.

Ms received April 15, 1986

SELOSTUS

Suomalaisten kivennäismaiden emäksen-
neutralointikapasiteetti

Helinä Hartikainen
Helsingin yliopisto, maanviljelyskemian laitos,
00710 Helsinki

Laboratoriossa tehdyssä titrauskokeessa selvitettiin 84
maanäytteen (15 aitosavi-, 41 hiesusavi- tai hietasavi-,
20 hiesu- ja 8 hietanäytettä) kykyä neutraloida emästä.
Ilmakuiviin 5 g:n maaeriin lisättiin 50 ml emäsliuosta, jos-
sa oli 0, 0.3, 0.6, 0.9, 1.2 tai 1.5 mekv KOH ja ionivah-
vuus säädetty 0. l:ksi KCLIIä. Suspensioiden annettiin
reagoida 4 päivää, minkä jälkeen niiden pH mitattiin.
Emäksenneutralointikapasiteetti ratkaistiin graafisesti
käyrältä, jossa mitattu pH esitettiin emäslisäyksen (mekv
kg-' maata) funktiona. Se ilmoitettiin emäsmääränä
(mekv kg-1 ), joka tarvittiin nostamaan maan pH 7:ään.

Emäksenneutralointikapasiteetti (BNC 7) vaihteli 0—

316 mekv kg-1 . Keskimääräinen BNC7 näytti olevan
aitosavissa selvästi suurempi (165 mekv kg-') kuin hiesu-
ja hietasavissa (102 mekv kg-') tai hiesujen ja hietojen
muodostamassa maalajiryhmässä (82 mekv kg-1). Koko
aineistossa saveksen pitoisuus korreloi kuitenkin suhteel-
lisen löyhästi BNC 7:n kanssa ja selitti vain 25 % sen

vaihtelusta. Maa-aineksen ominaisuuksien jaBNC 7:n vä-
listä suhdetta kuvaavissa regressioyhtälöissä savespitoi-
suus oli merkitsevä selittäjä vain hiesu- ja hietasavista
muodostetussa maalajiryhmässä. perusteella
BNC, riippui kaikissa maalajiryhmissä voimakkaimmin
maan alkuperäisestä pH:sta I. happamuuden intensitee-
tistä. Myös orgaaninenhiili ja oksalaattiuuttoinen AI oli-
vat merkitseviä selittäjiä. Näiden happamuuden luonnetta
ja kapasiteettia kuvaavien tekijöiden merkitys eri maa-
lajiryhmissä näytti kuitenkin jonkin verran vaihtelevan:
AI oli suhteellisesti tärkeämpi hiesu- ja hietasavissa, or-
gaanisen hiilen pitoisuus hiesu- ja hietamaissa, mutta
aitosavissa kumpikin tekijä oli yhtä tärkeä. Koska kalki-
tustarpeen arvioinnin tulisi perustua maan lähtö-pH:n li-
säksi myös happamuuden kapasiteettitekijöihin, tulos viit-
taa siihen, että kivennäismaille annettavia kalkitussuosi-
tuksia laadittaessa on syytä kiinnittää huomiota eri maa-
lajien välisiin eroihin.

46