This article was downloaded by: [Universitaetsbibliothek Heidelberg]On: 16 November 2014, At: 04:20Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

Soil Science and Plant NutritionPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/tssp20

Rates of soil acidification under different patterns ofnitrogen mineralizationKei Nambu a , Takao Kunimatsu b a & Kazutake Kyuma aa Faculty of Agriculture , Kyoto University , Sakyo-ku, Kyoto , 606-01 , Japanb Faculty of Agriculture, Shiga Prefectural Junior College , Kusatsu , 525 , JapanPublished online: 04 Jan 2012.

To cite this article: Kei Nambu , Takao Kunimatsu & Kazutake Kyuma (1994) Rates of soil acidification under differentpatterns of nitrogen mineralization, Soil Science and Plant Nutrition, 40:1, 95-106, DOI: 10.1080/00380768.1994.10414282

To link to this article: http://dx.doi.org/10.1080/00380768.1994.10414282

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) containedin the publications on our platform. However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of theContent. Any opinions and views expressed in this publication are the opinions and views of the authors, andare not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon andshould be independently verified with primary sources of information. Taylor and Francis shall not be liable forany losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoeveror howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use ofthe Content.

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

Soil Sci. Plant Nutr., 40 (1), 95-106, 1994

Rates of Soil Acidification under Different Patterns of Nitrogen Mineralization

Kei Nambu, Takao Kunimatsu*, and Kazutake Kyuma

Faculty of Agriculture, Kyoto University, Sakyo-ku, Kyoto, 606 - 01 Japan: and • Faculty of Agriculture, Shiga Prefectural Junior College,

Kusatsu, 525 Japan

Received March 24, 1993; accepted in revised form August 17, 1993

To evaluate the relative significance of acid deposition in a forest-soil system, H+-generating and -consuming conditions in the whole system were quantified based on the determination of the H+ budget. The two sites selected for this study displayed different rates of nitrification, which affected significantly the rates of soil acidification. Since at one site (MIKAMI), 60% of the total acid load was attributed to nitrification, the depletion of the soil acid-neutralizing capacity (ANC(s) was three and a half times faster than that of the other site (YASU). The decreasing rates of ANC(s) were 5.9 kmol ha- l y-I at MIKAMI and 1.7 kmol ha- l y-I at YASU, which are classified as sites with "intermediate" and "low" rates of soil acidification, respectively. Atmospheric input of H+ account­ed for only a small part « 10%) of the total acid load.

Comparison of the drainage at two depths (40 and SO cm) provided informa­tion about the mechanisms by which dissolved AIH was retained in soil. The YASU soil showed a high sulfate adsorption capacity, which resulted in rise of the solution pH by one unit, and subsequently in the precipitation of dissolved AP+ as jurbanite. In contrast, at MIKAMI, acid neutralization did not occur in the soil at 40- to SO-cm depths, but the cation exchange reaction decreased the concentration of dissolved AlH.

Key Words: acid-neutralizing capacity of soil, jurbanite, nitrification, proton budget, soil acidification.

95

There is a growing concern about the effect of atmospheric acid deposition on soils. Once soil has been acidified, it can affect considerably the ecosystems including forests, rivers, lakes, etc. The mechanisms of soil acidification, which in turn control the mechanisms of acid neutralization, have been well documented theoretically (Reuss and Johnson 1986; Binkley et al. 1989). However, processes actually occurring in a real field have not been sufficiently analyzed quantitatively. Moreover the effect of acid precipitation on the soils of Japan has not been clearly documented, partly due to the inherent acid properties of the soils in this country.

To analyze and predict the effect of acid deposition, it is necessary to estimate the rate of naturally generated acid, as a basis for the evaluation of acid deposition associated with human activities. van Breemen et al. (1984) proposed a method of determination of the H+ budget by which they quantified the total amount of H+ generated and consumed in a forest-soil system, dividing it into several major components. As their method is based on

Dow

nloa

ded

by [

Uni

vers

itaet

sbib

lioth

ek H

eide

lber

g] a

t 04:

20 1

6 N

ovem

ber

2014

96 K. NAMBU, T. KUNIMATSU, and K. KYUMA

the input-output budget of substances in the whole system, this method should be suitable for the above purpose. They observed that NH4 + derived from the atmosphere was nitrified in soils and acted as a proton source, and that the amount of H+ produced in the N transformation exceeded the amount of H+ directly deposited by rain. They noted that a high rate of acid load on acid soil caused a higher rate of Al20 3 dissolution and export of H+ and AP+ in drainage water.

They also introduced the parameter ANC(s) as an index of Acid Neutralizing Capacity of ~oil. Since ANC(s) is a capacity factor, it directly refers to proton addition and depletion, unlike an intensity factor such as pH. ANC(s) was defined as follows:

ANC(s) =2(Na20)+ 2(K20) + 2(CaO) +2(MgO) +6(AI20 3) + 2(MnO) + 2(FeO) - 2(S03) - 2(P20 5 ) - (HCl),

where parentheses denote the molar concentration, and the reference pH is 3. Based on the decreasing rate of ANC(s)(Ll ANC(s)) they classified twenty-one samples into three categories: low rate of soil acidification (Ll ANC < 2.5 kmol ha- 1 y-l), intermediate rate (2.5 to 7.5 kmol ha- 1 y-l), and high rate (>7.5 kmol ha- 1 y-l).

Based on this method, we attempted to analyze quantitatively the H+ -generating and -consuming conditions at our study sites. The purposes of this paper are as follows: 1) to determine the rate of soil acidification (Ll ANC(s)) under different rates of acid load depending on the pattern of N mineralization; 2) to evaluate the relative significance of atmospherically derived H+, compared with H+ generated by nitrification and other internal sources; and 3) to investigate the acid-neutralizing mechanisms in reference to the control of AI3+ concentrations, which is important from the viewpoint of toxicity to plants.

MATERIALS AND METHODS

1. Study area and characteristics of the soils. The two study sites were located 10 km east of Lake Biwa, Shiga Pref., in Central Japan (Fig. 1). The soils contained few alluvial sediments from the River Yasu. The parent materials were derived from cherty sedimentary rocks. Y ASU soil, located at the foot of Mt. Mikami, showed a silty clay texture with a pH of 4.5. The soil was classified as fine loamy mixed thermic typic Udorthent. Y ASU was covered by a Chamaecyparis obtusa forest of ca. 30 y of age that had taken over a Pinus densiflora forest through succession. The MIKAMI soil located at 1.5 km west of Y ASU and covered by a Chamaecyparis obtusa plantation forest of over 100 y of age, showed a sandy to clay loamy texture, with a pH of 4.5. The soil was classified as coarse loamy mixed thermic typic Udorthent (Soil Survey Staff 1992). Table 1 shows the properties of the two soils. As both were characterized by a fiat topography, no surface run-off was anticipated. No impermeable layer was found within the surveyed depths.

2. Experimental design. In relation to the input-output budget of substances, mineral elements in the precipitation were considered as the input. Minerals drained out of the profile and accumulated in the biomass were considered to represent the output from the soil. Precipitation was monthly gathered with a PVC funnel 30 cm in diameter in an open field located 2 km north of the above sites. For drainage, the soil solutions were sampled on the days following rainfall events at 40 and 80 cm depths using porous ceramic cups in duplicate. A negative suction of 67 kPa was applied on to the porous ceramic cups. After 24 or 48 h, 20 to 250 mL of the soil solution were collected. Throughout the year the moisture tension observed on the sampling occasions was nearly constant at 16 kPa at 40 cm depth and at 30 kPa at 80 cm depth at both sites. Water tension below 10 kPa had never been

Dow

nloa

ded

by [

Uni

vers

itaet

sbib

lioth

ek H

eide

lber

g] a

t 04:

20 1

6 N

ovem

ber

2014

Rate of Soil Acidification in Forest-Soil Systems

Fig. 1. Location of the study sites.

MIKAMI ·YASU

lOkm

97

observed even during heavy rain (> 50 mm/a night). Porous ceramic cups were installed in an area with a diameter of 2 m, 1.5 m apart from the nearest tree. The study period extended from Nov. 1991 to Oct. 1992.

3. Analytical methods. Soil solution pH was measured with a glass electrode within a day of sampling. Samples were kept at 4°C until further analyses: after filtration through a 0.45.um millipore filter the concentrations of Na+, K+, Ca2+, Mg2+, and NH4 + were measured by high performance liquid chromatography with an IC-C2 column, Cl-, N03 -, S04 2- with an CLC-ODS column (Shimadzu, LC-6A), AJ3+, Fe2+, Mn2+ by ICP-AES (N ippon Jarrell-Ash, ICAP-750). No H 2P04 - was detected.

To compare the nitrogen mineralization patterns at the two sites, we incubated the samples taken from the F-H layer and A horizon, in Aug. and Dec., 1992. Within 4 d we performed the following experiment. The soil samples were sieved with a 2 mm sieve without drying. The moist soil sample, corresponding to 10 g air-dried soil, in a 100 mL Erlenmeyer flask was incubated at 30°C for 30 d. Before and after incubation, non-dried soil (5 g on air-dried basis) was extracted with 2 M KCI, and then the contents of NH4 + and N03 - were determined by the steam distillation method (Bremner and Keeney 1966). All the experimen­tal steps were duplicated.

Fractions of free oxides were extracted from the air-dried samples with the following extractants: 1) 0.2 M (NH4)2C204H2 adjusted to pH 3.0 (McKeague and Day 1966), and 2) dithionite citrate bicarbonate (Mehra and Jackson 1960). It is considered that extraction 1) removes organically bound and inorganic amorphous sesquioxides (Alo, Feo), and extrac­tion 2) removes organically bound, inorganic amorphous, and crystalline sesquioxides (AId, Fed) (McKeague et al. 1971). The amount of crystalline Fe (Fee) was determined by subtracting the amount of Feo from that of Fed.

The index of adsorption capacity of sulfate was determined on air-dried soil according to the method of Fuller et al. (1985). Three grams of the soil were equilibrated with 30 mL of a I mM Na2S04 solution by shaking for an hour. Subsequently the sample was extracted with 30 mL of water, followed by 30 mL of 0.016 M NaH2P04. Each extractant was consid­ered to determine the potential of "water soluble" and "adsorbed SO/-," respectively, and

Dow

nloa

ded

by [

Uni

vers

itaet

sbib

lioth

ek H

eide

lber

g] a

t 04:

20 1

6 N

ovem

ber

2014

Tab

le l

. S

elec

ted

prop

erti

es o

f th

e st

udy

site

s.

YA

SU

C

lass

ific

atio

n: f

ine

loam

y m

ixed

the

rmic

typ

ic U

dort

hent

; pa

rent

mat

eria

l: c

hert

, gr

anit

e; v

eget

atio

n: C

harn

aecy

pari

s ob

tusa

nat

ural

for

est,

abou

t 30

y o

ld;

topo

grap

hy:

leve

l (3

%)

foot

of

Mt.

Mik

ami,

125

m a

bove

the

sea

lev

el.

Dep

th

pH

B

ase

C

Aid

F

eo

Fed

C

lay

Hor

izon

(e

m)

Col

or

Str

uctu

re"

Tex

ture

(H

2O

) C

EC

b sa

t. (%

) E

x. A

lb

min

rl.c

(10-

2 kg

kg-

I)

L

+ 1

.5-+

I 38

.1

FH

+

1

-0

4.01

22

.2

HA

-4

7.

5YR

3/3

2 m

cru

mb

SiC

L

3.76

51

.8

l.l

11.2

21

.4

0.38

0.

34

0.76

K~Vt>M

Bw

-2

0

5Y

R5

/8

2 m

a.b

lk

CL

4.

23

7.7

2.2

3.8

0.7

0.27

0.

08

1.04

K~AI-Vt,Vt

C

-41

5Y

R5

/6

none

S

iC

4.46

11

.3

1.2

5.3

0.3

0.35

0.

05

1.37

K~AI-Vt

2C

-50

IOY

R5/

8 no

ne

CL

4.

46

4.2

2.7

2.3

0.2

0.26

0.

05

1.08

K~AI-Vt

3C

-65

7.5Y

R5/

8 no

ne

SiC

4.

49

8.3

1.7

3.2

0.2

0.38

0.

05

1.52

K~AI-Vt

4C

-85

+

IOY

R5/

6 no

ne

SiC

L

4.52

7.

1 1.

9 2.

8 0.

2 0.

23

0.07

1.

23

K~AI-Vt

MIK

AM

I C

lass

ific

atio

n: c

oars

e lo

amy

mix

ed t

herm

ic t

ypic

Udo

rthe

nt;

pare

nt m

ater

ial:

che

rt;

vege

tati

on:

Cha

rnae

cypa

ris

obtu

sa p

lant

atio

n fo

rest

, m

ore

than

hun

dred

yea

rs o

ld;

topo

grap

hy:

flat

woo

ds,

105

m a

bove

the

sea

lev

el.

Dep

th

pH

B

ase

C

AId

F

eo

Fed

C

lay

Hor

izon

C

olo

r S

truc

ture

" T

extu

re

CE

Cb

Ex.

Alb

(c

m)

(H2O

) sa

t. (%

) (1

0-2

kg k

g-I)

m

inrl

.c

L

+1

.5-+

I

41.0

F

H

+1

-0

4.

32

13.9

A

-6

7.

5YR

2/1

2 m

eru

mb

S 4.

35

10.4

10

.5

1.5

3.4

0.03

0.

10

0.27

M

>K

>A

I-V

t C

-1

4

2.5Y

5/6

none

S

4.66

2.

4 8.

4 1.

3 0.

1 0.

06

0.06

0.

24

K>

M>

AI-

Vt

2A

-22

10Y

R3/

4 1

m s

.a.b

lk

SL

4.

46

6.8

5.4

3.7

1.2

0.18

0.

22

0.57

K

>M

>A

I-V

t,S

m

2C

-55

2.5Y

5/4

none

L

S 4.

65

4.9

4.3

3.1

0.2

0.10

0.

15

0.50

K

>M

>A

I-V

t,S

m

3CI

-63

2.5Y

4/6

1m

a.b

lk

CL

4.

55

9.9

3.2

5.1

0.2

0.15

0.

29

0.79

K

>M

>A

I-V

t,S

m

3C2

-105

IO

YR

4/6

none

C

L

4.49

9.

4 4.

0 4.

7 0.

2 0.

14

0.44

0.

79

K>

M>

AI-

Vt,

Sm

4C

-1

49

+

IOY

R4/

4 no

ne

CL

4.

59

9.4

5.3

5.0

0.3

0.17

0.

49

1.06

K

>M

>A

I-V

t,S

m

a G

rade

: I,

wea

k; 2

, m

oder

ate.

Siz

e: m

, m

ediu

m.

Typ

e: a

.blk

, an

gula

r bl

ocky

; s.

a.bl

k, s

uban

gula

r bl

ocky

. b

cmol

( +)

kg

-I s

oil.

C K

, ka

olin

min

eral

s; M

, m

ica;

V

t, ve

rmic

ulit

e; A

I-V

t, hy

drox

y-A

I in

terl

ayer

ed v

erm

icul

ite;

Sm

, sm

ecti

te.

<D

0

0

~

Z

;J>

~

tl:l

_C

>-l

:;><:

C

Z ~ ;J>

>-l

Vl

C - I>J

;:

l 0

- ~

:;><: ><:

C ~

;J>

Dow

nloa

ded

by [

Uni

vers

itaet

sbib

lioth

ek H

eide

lber

g] a

t 04:

20 1

6 N

ovem

ber

2014

Rate of Soil Acidification in Forest-Soil Systems 99

the latter was considered to correspond to the index of sulfate adsorption capacity. The amount of sulfate was determined by the colorimetric method described by Bertolacini and Barney (1957).

RESULTS AND DISCUSSION

Precipitation during the l-y study period was 1,465 mm, which corresponded to the average of the previous 10 y. The pH value of the rain ranged from 4.31 to 6.19, with a mode between 4.5 and 5.0, and hence it was considered that acid deposition did not affect this area severely.

1. Changes in soil solution 1) Cation composition. Figure 2 shows the concentrations of the major cations

observed throughout the study period, except for NH4 +, Fe2+, and Mn2+. Total cation concentrations at Y ASU were approximately 150 pmol L -I and did not vary seasonally, whereas those at MIKAMI fluctuated from 630 (40 cm May) to 2,130 ,umol L -I (40 cm Dec.). AP+, Ca2 +, and Na+ were the major contributors to the total cation composition at 40 cm at Y ASU, and at 40 and 80 cm at MIKAMI, while Ca2+ and Na+ were the major contribu­tors at 80 cm at Y ASU. On the other hand, the concentrations of K + and H+ were the lowest

10-0 mol L-i YASU 40cm

100

• 0

• • • 0 V 0

50 "s 0 • .. . 0 ~ 0

0 1 • .pJ . rl' . ~ . • 0 • v " v

"'. " . ~ . • o 0 . , v v 00 o 6 ~ 0

0 VV 0 o .l!. To v v v

~o 00 0 • 0 00 ~ . o 0 Q 0 • 0

0

o Na+ IJ. Ca2+ • AP+

o K+ H+

YASU 80cm 10-' mol L-i

100;-----------------------------~

o

00

50 0 • 0 . 0

o rP 0 ~ 00 0 0 g 0 • 0 •

" 0 • tP 0

0 0 0

~~ .~. e ~~ • 9 ~

i v • • ~ . I .• , • ., d I , 0

,~ D ,Jz F M A M ] J A S 0

10-' mol L-\ MlKAMl40cm

"0 1000 ..

. .. 500

·0

~ . " .. 0 .~ Hl o go l!. ~ ., ~ Vv v

~ ~~ .ee~~oe ~H ~; ~~ ~ o ~ o ,911 D ,Jz F M A M J J A S 0

o Nat IJ. Ca2t IIAP+

o K+ • H+

10-' mol L-I MlKAMI80cm

600 .. o • . .

300 0

0 0 0 . . .. o~ v

i" o ~ 9 v v v ' .. v v·

Oil' '"' u c ~ I'i.ll ~ °c a "

0 o ~ 00 o 0 0 ~o n ~ ~ 00 0 "0 e" ,911 D ,rjz F M A M J A S 0

Fig. 2. Seasonal variation of the concentrations of major cations at each depth. Scales on the vertical axes are not identical.

Dow

nloa

ded

by [

Uni

vers

itaet

sbib

lioth

ek H

eide

lber

g] a

t 04:

20 1

6 N

ovem

ber

2014

100 K. NAMBU, T. KUNIMATSU, and K. KYUMA

among all the cation species at both sites and depths, indicating that loaded acid was mostly neutralized.

At Y ASU the solution pH increased from around 4.5 to above 5.5 with depth, while at MIKAMI the pH remained unchanged at about 4.5 (Fig. 3).

At both sites the values of AI3+ decreased with depth, while those of the basic cations increased, the changes being more drastic at Y ASU than at MIKAMI (Fig. 2). At 80 cm at MIKAMI, the ratio of AI/basic cations increased along with the total cation concentration (Fig. 4), suggesting that higher concentrations of the solution resulted in the increase of the ratio of AI/basic cations. This phenomenon can be explained by an equilibration model of AI-Ca exchange reaction at a low base saturation (Reuss 1983).

2) Anion composition. The anion composition of the drainage water (Fig. 5) re­flected the origin of the acid. The most remarkable difference between the two sites was seen in the levels of N03 -. At Y ASU, N03 - contributed least to the generation of protons among the three anion species, while at MIKAMI, N03 - was the most important one, with a concentration ten to hundred times as high as that at Y ASU. This difference fully accounted for the difference in the concentrations of total cations between the two sites. Nitrate levels at MIKAMI also showed seasonal fluctuations, which were consistent with those of cations at corresponding depths (Figs. 2 and 5), indicating that cation leaching was largely influ­enced by the nitrate concentration. There was a time lag between the fluctuation curves at 40 and 80 cm. van Breemen et al. (1987) clearly demonstrated that the large amount of N03 -

generated in summer gradually percolated through the soil. The time required for N03 - to percolate from 40 to 80 cm varied with seasons: in the humid season N03 - percolated faster than in the dry season. See that it took 4 months (Dec. to Apr.) for the peak concentration of N03 - to reach the 80 cm depth, while the lowest concentration of N03 - took 2 months (May to Jul.) to reach the same depth. The amount of percolating water appeares to be responsible for the difference in the rate of percolation; in spring a large amount of rainfall and a relatively small amount of evapotranspiration accelerated the leaching of N03-.

As for SO/- and Cl-, the concentrations were nearly constant throughout the period, suggesting that the seasonal changes in the concentrations of N03 - may be due to the changes in the nitrification activity, rather than to those of organic nitrogen mineralization.

4.0

M A M J J A S a

o YASU 40cm • YASU 80cm

o MlKAMI 40cm • MIKAMJ 80cm

Fig. 3. Fluctuations of solution pH.

AI/basic cation

0.8 -

0.6 .. •• 0

o 00

o 0

0.4 -'r--..--,---,--~--.---r---r 800 1000 1200 1400

total cation concentration (1O-6mol L-ll

Fig. 4. Relationship between total cation con­centrations and the ratios of (Al)/(sum of con­centrations of basic cations) in soil solution at 80 cm (MIKAMll.

Dow

nloa

ded

by [

Uni

vers

itaet

sbib

lioth

ek H

eide

lber

g] a

t 04:

20 1

6 N

ovem

ber

2014

Rate of Soil Acidification in Forest-Soil Systems 101

10-6 mol L-l YA5U 40em 10-6 mol L-I MIKAMI40em 180

• 0 0 * 1600

* * . " * 0" 0 o 0 . ..

* 100 * V v 800 * ** * V 'IV v

V V V * * V V V V <tV * l V V V * V 'Iv .jik

*-ti<** ** * ***** He ... ~.~;~~ et 'il 'i'~ ~H ", 'i'~

0 0

,9'1 D ,ch F M A M J J A 5 0 ,9'; D ,J2 F M A M J J A S 0

* NO]- V CI- . SO/-

* NO]- V CI- . 50.2-

10-6 mol L-I YASU 80em 10-' mol L-I MlKAMI80em

1000

** 100

* * ** * v'V * * V V *** 50 "v 'V V 500 '\ * V V V V

V " ... 'Iv ** * ~ • , 'V e . eo • . * .. .

*** * ;:~; • • 0

.0 0 ~~ *-fIc** ** * *** ** * ** V V " ~'i'

. ~" w" " 0 0

,9'1 D '9J2

F M A M J J A S 0 ,9'1

D ,J2 F M A M J J A S 0

Fig. 5. Seasonal variation of anion concentrations at each depth. Scales on the vertical axes are not identical.

It should be noted that the sulfate concentrations at Y ASU decreased with depth, which will be discussed later.

2. Input-output budget and H+ budget In the input-output budget of substances (Table 2) the values for biomass accumulation

were cited from the survey ofIwatsubo (1976) in a 50-110 y Chamaecyparis obtusa natural forest. It should be emphasized that all the accumulated N was assumed to be in the form of nitrate and that the same values were applied to forests with different ages, which may lead to some error. Minerals supplied by direct precipitation were used as the input data; dry deposition on the plant surface was neglected, as it cannot be assesed. Drained quantity was calculated as the product of the concentration of the solution and flux of percolating water. For the estimation of the flux, we quoted the results obtained by Suzuki (1980), who estimated that the monthly evapotranspiration ranged from 17.0 (Nov.) to 96.8 mm (Jul.), based on the data collected in a catchment in southern Shiga Pref. The flux was, thus, estimated by subtracting the amount of evapotranspiration from the amount of observed precipitation. The annual percolation was estimated to be 707 mm. The l-y study was arbitrarily divided into 15 periods so that in each period a positive flux could be recorded. The concentration of each flux was represented by that of the solution collected at the end of the period.

Subsequently we tabulated the constituents contributing to H+ generation and con­sumption into the H+ budget table (Table 3).

1) L1 ANC(s)' L1 ANC(s), which is the rate of soil acidification, was determined for each

Dow

nloa

ded

by [

Uni

vers

itaet

sbib

lioth

ek H

eide

lber

g] a

t 04:

20 1

6 N

ovem

ber

2014

102 K. NAMBU, T. KUNIMATSU, and K. KYUMA

Table 2. Input-output budget of substances. YASU

H NH, Na K Ca Mg Al Fe Mn P2 O, CI NO, S04 (mol ha- 1 y-l)

Precip 293 306 422 149 257 113 13 420 324 668 Drain 28 27 283 82 102 316 16 0 4 0 357 98 226 Biomass 180 970 290 30 1,090

Net 265 279 140 -113 -815 -493 -16 0 -4 -17 63 -865 442

MIKAMI

H NH, Na K Ca Mg Al Fe Mn P2 O, CI NO, SO, (mol ha- 1 y-l)

Precip 293 306 422 149 257 113 13 420 324 668 Drain 411 17 1,139 157 1,260 1,453 2,553 4 96 0 1,092 4,238 1,233 Biomass 180 970 290 30 1,090

Net -118 289 -717 -188 -1,973 -1,631 -2,553-4 -96 -17 -672 -5,004 -565

Precip, input substances from direct precipitation; Drain, leached out substances from the soil at a depth of 80 cm; Biomass, assimilated substances by the plants, quoted from Iwatsubo (1976), all the nitrogen was assumed to be in the form of NO, -; Net, positive figures denote accumulation, negative ones eluviation in the 80 em-layer of soil. -, no data.

site: -1.7 kmol ha- 1 y-l at Y ASU, and - 5.9 kmol ha- I y-I at MIKAMI. Basic cations were the largest constituents contributing to L1 ANC,s). These values may correspond to "low" and "intermediate" rates of acidification, respectively, according to van Breemen et al. (1984).

2) Origin of loaded acid. The atmospheric input of H+ remained a minor « 10%) contributor to the total H+ generation (Table 3, external ratio). Acceleration, if any, of soil acidification could not be attributed to rain in our study area.

Nitrogen transformation played the largest role in the H+ generation at MIKAMI (Table 3). There could be an overestimation, as we assumed that the nitrogen assimilated by the vegetation was all in the form of nitrate, and that as much nitrate was generated in soil. The nitrogen transformation should be evaluated for its net effect: net proton generation associated with nitrogen transformation (NPG) was determined by the following equation:

NPG = (NH4)ln + (N03)out - (NH4)out - (N03)ln, (1) where NPG is the balance between the "N-trans" of H+ sink and the "N-trans" of H+ source listed in Table 2. The positive value of Eq. I indicates the consumption of NH4 + and the formation of N03 -, namely the occurrence of nitrification. The value of Eq. I at MIKAMI was 4.20 kmol ha- I y-I, whereas at Y ASU it was 0.05 kmol ha- I y-I. The results of soil incubation (Table 4) supported this observation, suggesting the presence of a high rate of nitrification for the FH layer at MIKAMI, and negligible nitrification for the Y ASU soil.

The difference in the nitrogen mineralization patterns resulted in differences in the efficiency of nitrogen retention in the soil-vegetation systems. At Y ASU the sum of the amounts of drained-out NH4 + and N03 - was smaller than the input (Table 2), suggesting that atmospherically supplied N was efficiently retained mostly in the vegetation. Ammo­nium cations must have been held by a cation exchange complex after release due to organic matter mineralization. At MIKAMI, however, the amount of drained N exceeded the input by more than 6 times, suggesting a higher rate of leaching than plant assimilation in terms of nitrate. The ecosystem of MIKAMI was depleting the nitrogen pool of the soil, for which

Dow

nloa

ded

by [

Uni

vers

itaet

sbib

lioth

ek H

eide

lber

g] a

t 04:

20 1

6 N

ovem

ber

2014

Rate of Soil Acidification in Forest-Soil Systems 103

Table 3. H+ budget of soil at 80 cm depth.

H+ sources Ex- H+ sinks

CO B· Org.mat. ternal Bio- Ll Rain N-trans Sum Weather N-trans Stream Sum

2 IOmass minrlz ratio mass ANC (kmol ha~l y-') (%) (kmol ha~l y-')

YASU 0.29 1.49 0.06 1.44 0.00 3.29 8.9 1.74 0.09 1.44 0.Q3 3.31 -1.74 MIKAMIO.29 5.63 0.41 1.44 1.27 9.05 3.2 7.16 0.03 1.43 0.41 9.03 -5.89

H+ sources include: (I) atmospheric input of H+; gaseous SO, is not taken into consideration: (H+)ln. (2) potentially generated H+ in N transformation, particularly nitrification: (NH')'n + (NOa)out + (NOa)blO. (3) dissociation of H,COa and organic matter, which was estimated from the discrepancy in the charge balance. (4) net accumulation of cations in biomass: (K+Ca+Mgh,O. (5) net anion release by mineralization of organic matter; ammonium and nitrate are not included: (Cl +SO.)out - (Cl+ SO.)ln + (P,O')bIO. H+ sinks include: (I) exchange reaction by and weathering of soil: (Na+K+Ca+Mg+AI+Fe+Mn)out-(Na+K+ Ca+ Mg),n - (K +Ca+ Mg)bIO. (2) net anion accumulation in biomass; nitrate is not included: (P,O')bIO. (3) potentially consumed H+ in N transformation and nitrate assimilation: (NH.)out + (NOa),n + (NOa)bIO. (4) exported H+ in the drainage water: (H+)out. (element),n, (element)out, (element)b'o denote the element in atmospheric input, drainage, and biomass assimilation indicated in Table 2, respectively. External ratio is calculated as (atmospheric input of H+) X 100/(the sum of generated H+). Only the atmospheric input of H+ is assumed to consist of H+ of external origin. Ll ANC (acid neutralizing capacity) is determined as (Minrlz) - (Weather), which corresponds to the index of the rate of soil acidification. Elements without data in Table 2 are not included in the budget, which can lead to some error.

Table 4. Patterns of nitrogen mineralization at the two study sites.

pH (H 2O) (NH. + NOa-N) NOa-N Proportion of nitrified N

1:10 tug g~l soil d~l)

YASU FH Aug. 4.01 5.5 0.0 0.00 Dec. 3.34 10.5 0.3 0.03

HA Aug. 3.79 0.5 0.0 0.00 Dec. 4.04 1.3 0.0 0.00

MIKAMI FH Aug. 4.32 4.5 4.4 0.98 Dec. 3.72 9.0 4.3 0.48

A Aug. 4.46 1.4 1.2 0.86 Dec. 4.16 1.8 1.7 0.94

(NH. + NO.), (NOa)-N denote the rate of net N-mineralization and net nitrification, respectively, based on 30-d incubation of fresh soil.

a high rate of nitrification was likely to be responsible. Various examples quoted by van Breemen et al. (1984) showed that soils with pHs of

4 to 5 contained similar amounts of H+ sources except for N transformation and atmospher­ically derived H+. Nitrification, rather than direct input of H+, was the main factor which controlled the rate of soil acidification. Their results showed that I) soils with a NPG above 1.0 kmol ha- 1 y-l display an "intermediate rate" of acidification, and 2) soils with a NPG below 1.0 kmol ha- 1 y-l a "low rate." Despite the fact that the ammonium substrate in the quoted cases was derived from (NH4)2S04 deposition, this generalization may be applied to the results of our study. We found that nitrification from internal origin served as a large H+ source at MIKAMI, where the soil was displaying an intermediate rate of acidification.

As for the proton generation at Y ASU, the net cation assimilation by the biomass accounted for one-third of the total (Table 3). It must have been the largest acid generator, in view of the possible overestimation of the nitrogen transformation.

Dow

nloa

ded

by [

Uni

vers

itaet

sbib

lioth

ek H

eide

lber

g] a

t 04:

20 1

6 N

ovem

ber

2014

104 K. NAMBU, T. KUNIMATSU, and K. KYUMA

Table 5. Composition of leachate at each depth.

H NH, Bas.Cat." Al CI NO, SO,

(kmol ha-1 y-l)

YASU 40cm 0.20 0.02 0.83 0.34 0.38 0.05 0.81 80 cm 0.03 0.03 0.78 0.02 0.36 0.10 0.23

----------------------- ------------------------------------------------------. Change -0.17 0.00 -0.05 -0.32 -0.02 0.05 -0.58

MIKAMI 40cm 0.43 0.02 3.29 3.22 1.06 4.36 1.32 80 cm 0.41 0.02 4.01 2.55 1.09 4.24 1.23

---------------------------------- --------------------------------------------Change 0.02 -0.01 0.72 -0.66 0.03 0.12 0.09

" Denotes the sum of the amount of basic cations.

MlKAMI YASU

10 13

adsorbed sulfate

n 3

D water soluble sulfate

Depth

3. Dynamics of dissolved aluminum

Fig. 6. Amount of soluble (water extractable) and adsorbed (phosphate extractable) SO/­from MIKAMI and Y ASU soils. The concentration of insoluble sulfate is an index of the sulfate adsorption capacity.

Mechanisms which control the composition of the soil solutions should be examined in relation to soil properties. Table 5 illutrates the changes in the solution composition between the two depths. Due to the low organic matter content and fewer roots, these changes can be attributed to reactions taking place only between the mineral soils and the solutions. It should be noted that although aluminum was retained by the soil at depths between 40 and 80 cm at both sites, the mechanisms involved were different between the two sites.

At MIKAMI the concentration of aluminum decreased by 0.66 kmol ha- 1 y-l during percolation through soil from 40 to 80 cm depths. Since the concentrations of the basic cations in the solution increased substantially (0.72 kmol ha- 1 y-l), the decrease of the concentration of aluminum can be explained by the exchange with basic cations.

However this mechanism did not apply to the Y ASU soil, where the concentrations of both aluminum and other cations decreased with depth. In addition, SO/- was retained in the same process. Figure 6 shows that the S04 2--adsorbing capacity as measured by the NaH 2P04 elution increased in the 3C and 4C horizons of the Y ASU soil (50 to 85 cm). The content of free iron and aluminum oxides may account for the difference in the capacity of sulfate adsorption between the two sites. Based on a regression analysis (Table 6) of SO/­adsorption capacity and free oxide fractions, the capacity was significantly correlated with

Dow

nloa

ded

by [

Uni

vers

itaet

sbib

lioth

ek H

eide

lber

g] a

t 04:

20 1

6 N

ovem

ber

2014

Rate of Soil Acidification in Forest-Soil Systems

Table 6. Correlation coefficients (r) from linear regression analysis for insoluble SO;- versus soil properties.

105

Alo Feo (AI+Fe)o AId Fed (AI+Fe)d Fec C% Clay P-retention

0.45 -0.27 -0.035 0.79" 0.64* 0.70*' 0.66* 0.41 -0.47 0.62*

n= 13. '," Significant correlation coefficient at the 5 and 1% confidence levels, respectively. Fec, defined as (Fed- Feo).

12

0 0

10

3pH-pA)3+

8

.' 6

11 13 15

2pH+pSO.2-

jurbanite pK,p=17.80

0 0 0

0 0 0 0 0

0

~ 0

0 00

17

pK,p=32.34

• 40cm of YASU

o 80em of YASU

Fig. 7. Equilibrium diagram for amorphous AI(OH)3, and jurbanite AI(OH)SO •. Note that Aj3+ and SO.'- concentrations in Y ASU solution decreased along the jurbanite line with depth.

the amount of dithionite-extractable Fe and Al fractions and Fec (Fed - Feo, crystalline iron oxide ), which was consistent with the results obtained by Johnson and Todd (1983). Hence, the DeB soluble fraction is considered to playa role in the adsorption of sulfate.

As a result of sulfate adsorption, hydroxide ion should have been released to the bulk solution via ligand exchange (Parfitt and Smart 1978; Rajan 1978). In view of the decrease of the concentration of aluminum from the 40 to 80 cm depths with the increase of the pH, it is assumed that Al may have precipitated as Al hydroxides. Figure 7 is an equilibrium diagram for amorphous AI(OH)3 (pKsp =32.34), and jurbanite (pKsp= 17.80), the precipita­tion of both of which being enhanced at a high pH. The values of pKsp were cited from Lindsay and Walthall (1989). Activity coefficients were calculated using the extended Debye-Hiickel equation, as the ionic strengths were well below 0.1 M:

log YI = -0.509ZI2(UI/2j(1 + Ul/2 )-0.3u).

Yi> activity coefficient; ZI> valency of the ion concerned; u, ionic strength. N one of the Al is assumed to be bound to organic acid, and even if half of the amount.

of Al was bound, the graph would remain almost unchanged. As the plots of the solutions from the 40 cm depth lay closely under the jurbanite line but also below the line of amorphous AI(OH)3' it is suggested that they were derived from the dissolution of amor­phous AI(OH)3 or precipitated as jurbanite. On the other hand the plots of the solutions from the 80 em depth, which contained lower concentrations of both AIH and SO/-, were scattered above the equilibrium line for amorphous Al(OH)3 but below the jurbanite line. The precipitation of jurbanite is likely to have acted as a mechanism of control of AIH and S042- concentrations in this higher range of pH (above 5.5). Although for the formation of jurbanite SO/- anion is consumed in the solution, its contribution was not as large as that

Dow

nloa

ded

by [

Uni

vers

itaet

sbib

lioth

ek H

eide

lber

g] a

t 04:

20 1

6 N

ovem

ber

2014

106 K. NAMBU, T. KUNIMATSU, and K. KYUMA

of sulfate adsorption. Even though all of the decrease in the amount of AP+ (0.32 kmol ha-1

y-l) was due to jurbanite formation, the amount of SO/- consumed in that process should not exceed 0.21 kmol ha-1 y-l, which is well below the total amount (0.58 kmol ha- 1 y-l). In conclusion, in the case of Y ASU, sulfate adsorption in the lower horizons resulted in the increase of the pH by one unit; the higher pH further brought about the precipitation of jurbanite which consumed AI3+ and S04 2

- in the soil solution. In a soil with a low base saturation such as Y ASU, it is assumed that sulfate adsorption may be an important mechanism of acid neutralization.

Acknowledgments. We wish to express our gratitude to Dr. Hideaki Hirai, who read the manuscript and made valuable comments, and to Mr. Miki Sudo for his helpful suggestions in the selection of the study sites. We thank Associate Professor Takasi Kosaki for his assistance. This research was supported in part by a grant from the Nihon Seimei Foundation.

REFERENCES

Bertolacini, R.1. and Barney, J.E. 1957: Colorimetric determination of sulfate with barium chloranilate. Anal Chern., 29, 281-283

Binkley, D., Driscoll, C.T., Allen, H.L., Schoeneberger, P., and McAvoy, D. 1989: Acidic Deposition and Forest Soils, 149 pp., Springer-Verlag, New York

Bremner, J .M. and Keeney,D.R. 1966: Determination and isotope-ratio analysis of different forms of nitrogen in soils: 3. Exchangeable ammonium, nitrate, and nitrite by extraction distillation methods. Soil Sci. Soc. Am. Proc., 30, 577-582

Fuller, R.D., David, M.B., and Driscoll, C.T. 1985: Sulfate adsorption relationships in forested spodosols of the north eastern USA. Soil Sci Soc. Am. J., 49, 1034-1040

Iwatsubo, G. 1976: Cycling of plant nutrients in a forest ecosystem, the role of precipitation. In Mountains, Forests and Ecology, Ed. T. Kato, S. Nakao, and T. Umesao, p. 313-360, Chuoh Kohron, Tokyo (in Japanese)

Johnson, D.W. and Todd, D.E. 1983: Relationships among iron, aluminum, carbon, and sulfate in a variety of forest soils. Soil Sci. Soc. Am J., 47, 792-800

Lindsay, W.L. and Walthall, P.M. 1989: The solubility of aluminum in soils. In The Environmental Chemistry of Aluminum, Ed. G. Sposito, p. 221-240, CRC Press, Florida

McKeague, J.A., Brydon, J.E., and Miles, N.M. 1971: Differentiation of forms of extractable iron and aluminum in soils. Soil Sci. Soc. Am Proc., 35, 33-38

McKeague, J.A. and Day, J.H. 1966: Dithionite- and oxalate-extractable Fe and Al as aids in differentiating various classes of soils. Can. J. Soil Sci, 46, 13-22

Mehra, D.P. and Jackson, M.L. 1960: Iron oxide removal from soils and clays by a dithionite-citrate system buffered with sodium bicarbonate. In Proc. 7th Nat!. Conf. on Clays and Clay Minerals, p. 317-327

Parfitt, R.L. and Smart, R.S.C. 1978: The mechanism of sulfate adsorption on iron oxides. Soil Sci Soc. Am ]., 42, 48-50

Rajan, S.S.S. 1978: Sulfate adsorbed on hydrous alumina, ligands displaced, and changes in surface. Soil Sci. Soc. Am. J., 42, 39-44

Reuss, J.~. 1983: Implication of the calcium-aluminum exchange system for the effect of acid precipitation on soils. J. Environ. Qual, 12, 591-595

Reuss, J.~. and Johnson, D.W. 1986: Acid Deposition and the Acidification of Soils and 119 pp., Waters, Springer-Verlag, New York

Soil Survey Staff 1992: Keys to Soil Taxonomy, 5th ed., SMSS Technical Monograph No. 19, 541 pp., Pocahontas Press, Virginia

Suzuki, M. 1980: Evapotranspiration from a small catchment in hilly mountains (I), seasonal variations in evapotranspiration, rainfall interception and transpiration. J. Jpn. For. Soc., 62, 46-53

van Breemen, N., Driscoll, c.T., and Mulder, J. 1984: Acidic deposition and internal proton sources in acidification of soils and waters. Nature, 307, 599-604

van Breemen, N., Mulder, J., and van Grinsven, J.J.M. 1987: Impacts of acid atmospheric deposition on woodland soils in the Netherlands: 2. Nitrogen transformations. Soil Sci Soc. Am. J., 51, 1634-1640

Dow

nloa

ded

by [

Uni

vers

itaet

sbib

lioth

ek H

eide

lber

g] a

t 04:

20 1

6 N

ovem

ber

2014