J. Jpn. Soc. Soil Phys.
土壌の物理性No. 141 p.3 ∼ 18 (2019)

Effects of soil amendmentson pH and aggregate stability of saline sodic soil
and acid sulfate soil in Mekong delta, Viet Nam
Ca Thi NGUYEN1 , Shoichiro HAMAMOTO1 and Taku NISHIMURA1

Abstract: Acid sulfate soils and salt-affected soils arewidely distributed in the Mekong Delta of Viet Nam. As
well as the improvement of chemical properties, it is essential to minimize soil structural degradation. However,relatively little research has been conducted on behaviors
of aggregates in the Mekong Delta. In the present study,saline and sodic soil (SS), alluvial soil (AS), and acid sulfate soil (ASS) were collected from the Mekong Delta.
First, aggregate stability tests were conducted on them.
Base on the aggregate stability test, dry clods of 2–5 mm
in size under fast wetting process were used to evaluate
aggregate stability of the soils after incubation with soil
amendments. Chicken manure was used as a compostand eggshell-CaCO3 was an alternative for lime. Soil andamendments were mixed and incubated in a glass bottle for
45 days at a constant temperature of 25 ◦ C. During the incubation, CO2 concentration in the headspace of the glass
bottle was periodically measured. After incubation, soil
pH and aggregate stability were evaluated. Mean weight
diameter (MWD) was used to evaluate aggregate stability. Eggshell application increased the pH of all three soils.
Compost raised the pH of SS and AS but it was less effective at raising pH of ASS. The combination of compost andeggshell was the most effective at increasing soil pH. Rapid
increases in CO2 emission rate after eggshell applicationsuggested that the CaCO3 rapidly reacted with the H+ inthe soils. Correlations between soil pH and CO2 emission
suggested that microbial activity increased with increasing
in soil pH. Eggshell application alone destabilized soil aggregates, whereas the compost and the compost-eggshellcombination improved aggregate stability.
Key Words : soil improvement, soil structure, chicken manure compost, eggshell, soil deterioration

1. Introduction
Approximately 65 % of the land in the Mekong Delta of
1 Department of Biological and Environmental Engineering, Graduate
School of Agricultural and Life Sciences, The University of Tokyo, 11-1 Yayoi, Bunkyo-ku Tokyo 113-8657, Japan. Corresponding author:
Ca NGUYEN THI2018 年 6 月 27 日受稿 2018 年 11 月 30 日受理

Viet Nam is used for agriculture (General Statistics Officeof Vietnam, 2015). However, salt-affected soil and acidsulfate soil prevalent there are reducing crop yields. Saltaffected soil has increased from 0.7 million ha to 0.88 million ha between 1975 and 2005 (Duc and Dao, 2011) andincreased to 1.4 million ha in 2011 (Viet Nam-Netherlands
Cooperation, 2011). Acid sulfate soils (ASS) decreased
from 1.8 million ha to 1.5 million ha between 1975 and2005 (Duc and Dao, 2011) and further declined to 1 million
ha by 2011 (Viet Nam-Netherlands Cooperation, 2011). To
ensure food security for rapidly growing populations, it isimperative to sustain soil productivity through proper agricultural practices.
Acid sulfate soil (ASS) is formed by the oxidation of
pyrites (FeS2 ) in the soil. Sulfuric acid (H2 SO4 ) is oneof the end products in pyrite oxidation, and it lowers soil
pH (Attanandana and Vacharotayan, 1986). At a depth of
0–100 cm, the pH range of ASS is from 2 to 4 (Attanandana and Vacharotayan, 1986; Minh and Tri, 2006). Whenthe pH < 4.0, the soluble forms of aluminum ion (Al3+ )and ferric ion (Fe3+ ) are abundant in the soil. The release of hydron (hydrogen ion, H+ ) from soluble Al3+ andFe3+ hydrolysis reduces pH of ASS (Iqbal, 2012; Strawn etal., 2015; Stefansson, 2007).
Saline and sodic soils (SS) have both high salinity andsodicity. They are classified on the basis of the electrolyte conductivity of their saturation extracts (ECe) (>4 dS m−1 ), pH (< 8.5), and exchangeable sodium percentage (ESP) (> 15 %) (USSL Staff, 1954). The soil structure of SS is fragile and susceptible to structural degradation. High ESP increases clay dispersion (Abu-Sharar etal., 1987). Clay particles disperse by the expansion of the
diffuse double layer around the particles (Shainberg andLetey, 1984; Abu-Sharar et al., 1987). Dispersed clayplugs soil pores and reduces soil hydraulic conductivity(Frenkel et al., 1978; Farahani et al., 2018).
Soil productivity is also affected by aggregate stability.

4

土壌の物理性

Stable soil aggregates support nutrient cycles, water andgas movement, and root respiration. Aggregate stability
is influenced by aggregate breakdown processes like fast
wetting, slow wetting, and mechanical breakdown (Le Bissonnais, 1996). Slaking by entrapped air occurs when dry
soils exposing to the fast wetting process. It corresponds
to the cases of sudden water application such as border andfurrow irrigation to dry soils. In the slow wetting process, water is gradually supplied to the soil, differential
swelling and physicochemical dispersion predominate aggregate breakdown. Raindrop impact is a mechanical action which can contribute to aggregate breakdown.
To make a good seedbed, 2–4 mm clods are recommended to create by tillage (Braunack and Dexter, 1988).
However, farmers often tend to till too much to makesmooth seedbed surface. In the study of Legout et al.
(2005), aggregates were less stable in the initially < 3 mm
clods than in the initially 3–5 mm, 5–10 mm, and 10–20mm clods.
Aggregate stability is affected by initial soil moisture
conditions, too. Aggregate stability increases with increase
in initial soil water content prior to immersion to water(Kemper and Rosenau, 1984). Under fast wetting process,initially moist aggregates of 2–4.75 mm in diameter weremore stable than initially dry aggregates of the same size
(Almajmaie et al., 2017). The relatively smaller volumesof entrapped air in initially moist aggregates may produce
less compression force under fast wetting than in initiallydry aggregates (Kemper and Rosenau, 1984; Vermang etal., 2009). Therefore, breakdown processes and initial conditions must be considered for aggregate stability analysis.
Liming is a common measure to increase pH of acidsoils. The pH increased from 5.1 to 5.6, 5.9, 6.4, and 6.8 in
response to CaCO3 application rates of 0.75, 1.5, 3.0, and
4.0 g CaCO3 kg-soil−1 , respectively (Whalen et al., 2002).
When the CaCO3 application rate increased from 4.0 to
10.13 g CaCO3 kg-soil−1 , pH of the acid sulfate soil increased to 4.51 and 6.10, respectively, from its initial, 3.19
(Khoi et al., 2010). However, liming may have adverse effects on soil structure. Liming increased clay dispersion
and decreased the infiltration rate of a Brazilian Oxisol 6
weeks after application (Roth and Pavan, 1991). The effects of liming on aggregate stability of acid sulfate soil
are not clear.
Compost improves soil fertility (Dikinya and Mufwanzala, 2010), enhances soil pH (Whalen et al., 2002), andstabilizes soil aggregates (Wortmann and Shapiro, 2008).
Whalen et al. (2002) reported that the pH of an acidic soil
increased from 5.1 to 6.2 after compost was applied at therate of 40 g kg soil−1 as dry matter. The pH of an acidsulfate soil rose from 3.19 to 4.16 with the addition of 62.5
g compost kg soil−1 and to 6.42 when 62.5 g compost kg

第 141 号

(2019)

soil−1 with 10.13 g CaCO3 kg-soil−1 was applied (Khoiet al., 2010). The pH rise after compost application was
explained by Al-organic matter complexes (Naramabuyeand Haynes, 2006a). This leaded to a reduction of soluble
Al3+ concentration by adding compost (Khoi et al., 2010).
Yan et al. (1996) reported the role of decarboxylation oforganic anions on the pH rise. Khoi et al. (2010) reported
rise in NH4+ -N and NO−
3 -N was a contributor of microorganism activity after compost application with or without CaCO3 to the acid sulfate soil. However, they did nothave the evidence of increase in micro-organism activity inacid sulfate soils after the either compost or combinationsof compost and CaCO3 . In addition, they did not consider
aggregate stability of acid sulfate soil after the amendment
application, neither.
The beneficial effects of organic matter on aggregate stability of sodic soil were reported by Quirk and Murray(1991) and Nelson and Oades (1998). Aggregate stability of saline sodic soil was improved by adding compost at
75 t ha−1 (Chaganti et al., 2015). Products from decomposition of organic matter help to form stable aggregates.
Micro-organisms decompose organic matter and releasemonosaccharides and/or polysaccharides which bind soil
particles and re-form soil aggregates (Griffiths and Jones,
1965; Tisdall and Oades, 1982). Microbial activity during
this process can be evaluated by CO2 emission rate. Soilphysico-chemical properties and amendment inputs influenced microbial activity. After 17 weeks incubation, soil
CO2 respiration of acid soils subjected to a combinationof lime and litter was higher than that of acid soils addedwith either lime or litter (Condron et al.,1993). The risein pH of acid soil in response to liming increased carbon
mineralization from microbial activity and reduced aggregate stability in the long term (Karcauskiene et al., 2015).
It is unknown about the effects of compost and CaCO3 application on changes in CO2 emission associated with pH
and soil aggregate stability in acid sulfate soil. Our hypothesis was that the combined application of compost andCaCO3 is more effective in improving saline and sodic soil
and acid sulfate soil than the application of either compost
or CaCO3 alone. The objectives of this study were to (1)determine the effects of breakdown processes, initial clod
sizes, and initial soil moisture on soil aggregate stability ofthe soils, (2) discuss the effects of compost and CaCO3 application on pH, CO2 emission, and aggregate stability ofsaline sodic soil and acid sulfate soil in the Mekong Deltaof Viet Nam.

2. Materials and Methods
2.1 Soil sampling site
Soil samples were collected at three sites in the Mekong

論文：Effects of soil amendments on pH and aggregate stability of saline sodic soil and acid sulfate soil

Delta, Viet Nam. Alluvial soil (AS) (Epigleyic Fluvisols:
FLglp) (N: 10◦ 06’48.8”; E: 105◦ 30’39.5”) sampled at thefield has continuously been used for Luffa Gourd growing
during seven years. Saline and sodic soil (SS) (Episalic
Solonchaks: SCszp) (N: 08◦ 34’40.5”; E: 104◦ 49’10.8”)
sampled at the field has been no crop during 2 years after
soil accretion. Acid sulfate soil (ASS) (Epi OrthiThionicFluvisols: FLtiop) (N: 09◦ 43’20.3”; E: 105◦ 22’46.8”)
sampled at the field has been continuously used for pineapple growing during 50 years. They were taken at a depthof 0–20 cm. Soil types were defined according to the map
inventory of the Mekong Delta following the World Reference Base for Soil Resources-Food Agriculture Organization of the United Nations at scale of 1/250, 000 (Minhand Tri, 2006) and World Reference Base for soil resourcesclassification systems (ISSS/ISRIC/FAO, 1998). Surface
litters and vegetation were removed before the samples
were collected. Then, they were packed in plastic bags andtransported to the laboratory with minimum disturbance ofthe natural soil structure.
2.2 Analytic methods of soil properties
Soil samples were air-dried and ground to pass through a
2-mm sieve. Soil pH was determined from 1 : 5 soil/water
extracts (McLean, 1982) using a LAQUAtwin pH meter(Horiba, Kyoto, Japan). EC1:5 was determined from 1:5
soil/water extracts (Rhoades, 1996) using a LAQUAtwin
EC meter (Horiba, Kyoto, Japan). ECe was derived fromthe EC1:5 and water content at saturation. Percent organic carbon (% OC) and total nitrogen (% N) were determined by dry combustion of the soil at 950 ◦ C by a
CN Element analyzer (Vario EL cube, Elementar Analysensysteme GmbH, Langenselbold, Germany). Soluble
Ca2+ , Mg2+ , and Na+ were measured in 1 : 5 soil/water
extracts using ion chromatograph. To prepare these extracts, 1 g air-dried soil was weighed and mixed with 5 mL
distilled water in a 50-mL centrifuge tube. The tube wasshaken for 30 min and centrifuged for 10 min at 5600×g.
The supernatant was passed through a 0.45-µ m filter. The
ion chromatograph system consisted of DGU20A, LC20A,
LC20AD, SIL10Ai, SCL10A, CDD10A, and CTO20A(Shimadzu corporation, Tokyo, Japan). The columns wereShim-pack IC-A1 (100 mm × 4.6 mm i.d. and 12.5 µ m
particle size) (Shimadzu Corporation, Tokyo Japan) and
Shim-pack IC-GA1 (10 mm × 4.6 mm i.d.) (Shimadzu
Corporation, Tokyo, Japan). The sodium adsorption ratio(SAR) was calculated as follows:[Na+ ]SAR = √([Ca2+ ] + [Mg2+ ])/2

(1)

where SAR is expressed in (mmolc L−1 )0.5 . [Na+ ], [Ca2+ ],and [Mg2+ ] are the Na+ , Ca2+ , and Mg2+ concentrations

5

in soil solution, and are expressed in mmolc L−1 . The exchangeable sodium percentage (ESP) was determined fromthe Gapon formulae:
KG
ESR = √
SAR
1000

(2a)

100 × ESR
1 + ESR

(2b)

ESP =

where KG is the cation selectivity coefficient and KG = 0.5(mmolc L−1 )−0.5 (Gapon, 1933). ESR is exchangeablesodium ratio. The field capacity was determined by ahanging water table at −100 cm H2 O (ψ = −10.1 kPa)
(Klute, 1986). The cation exchangeable capacity (CEC)
was measured by the ammonium acetate method (Sumnerand Miller, 1996). The soil texture was measured by the
Robinson pipette method (Gee and Bauder, 1986). The
dry bulk density (g cm−3 ) was measured by the undisturbed core method (Grossman and Reinsch, 2002). The
pycnometer method was used to determine the soil particle
density (g cm−3 ) (Blake and Hartge, 1986). The saturated
hydraulic conductivity (Ksat ) (cm s−1 ) was measured in saturated soil packed in 100 cm3 columns using the fallinghead method with tap water (Klute and Dirksen, 1986).
2.3 Preparation for aggregate stability test
Soil blocks collected in the fields were cut into pieces
smaller than 5 cm in size and left them at room temperature to reduce soil moisture to be proper moisture for handling. All soil sections were cut into square clods of 1–
3 mm, 2–5 mm, and 5–10 mm. This process simulated
the production of clods by tillage harrowing. The clods
were adjusted to two levels of soil moisture, namely, moist
and air-dried with water content ∼ 50 % and ∼ 5 %, respectively. Field wetness and dryness affecting aggregatestability were simulated in the laboratory using moist andair-dried clods.
2.4 Aggregate stability test
Aggregate stability was evaluated by fast wetting,slow wetting, and mechanical breakdown (Le Bissonnais,
1996). The procedures are described in a schematic diagram (Fig. 1). Fast wetting simulates aggregate breakdown caused by rapid soil immersion in water corresponding to heavy rainfall or furrow or border irrigation. Clods
were rapidly submerged in 100 mL deionized water for 10
min. Slow wetting simulates aggregate breakdown caused
by low-intensity rainfall. Clods were left on a tension tableconnecting with Mariotte bottle to supply water with a constant pressure of −3 cmH2 O for 6 hours to get moist condition. Mechanical breakdown simulates aggregate breakdown by mechanical force. Arai et al. (2003) and Le
Bissonnais (1996) proposed the use of ethanol to exclude
slaking by entrapped air,differential swelling and physico-土壌の物理性

6

第 141 号

(2019)

Fig. 1 Schematic diagram procedures for aggregate test with three treatments: fast wetting; slow wetting and mechanical breakdown.

chemical dispersion before the mechanical treatment. The
ethanol reduces the thickness of diffuse double layers. Attraction forces between O-H bonds of ethanol and clay
particles enable adjacent clay platelets to approach eachother and reduce physico-chemical dispersion (Emerson,
1957) before the mechanical agitation. In the mechanical breakdown process, clods were submerged once in
50 mL ethanol (99.5 % v v−1 ) for 10 min. The clods
were then placed in 250 mL Erlenmeyer flasks containing
200 mL water. The flasks were shaken end over end
for 20 times. The samples were then passed through a
0.053-mm mesh sieve to be separated into fragments< 0.053 mm and > 0.053 mm. Fragments < 0.053 mm
were defined by the differences between their initial massand the sum of the mass of the other six size fractions.
Those > 0.053 mm were passed through six nested sieves:
2 mm, 1 mm, 0.500 mm, 0.25 mm, 0.125 mm, and 0.053
mm. They were sieved by the Yoder sieve (Yoder, 1936).
After the three treatments: fast wetting, slow wetting andmechanical breakdown, aliquot of ethanol was added to thesamples to prevent additional aggregate breakdown before
wet sieving by Yoder sieve. Fragments remaining on thesieves were oven-dried at 105 ◦ C for 24 h. Aggregate stability in each treatment was expressed using the size distribution of the three fragments: d > 2mm; 2 mm> d >0.25 mm; and d < 0.25 mm. The mean weight diameter (MWD) was calculated from the mass fractions of theoven-dried samples (g) remaining on each sieve (after sieving) multiplied by the mean diameter (mm) of the adjacent
mesh:
MWD =

∑i=n
i=1 mi × di
∑ mi

(3)

where mi is mass of aggregate fraction (i) of soil remaining

on each sieve (after sieving) (g), and di is mean diameterof the adjacent mesh (mm).
Changes in MWD indicate that the clod size has decreased as a consequence of the breakdown caused by thethree treatments.
2.5 Preparation for soil incubation
In the actual field, the soil must be plowed into smaller
fragments to increase the contact surface area between theamendments and the soil particles. In the laboratory, thisprocess was simulated by passing the soil blocks througha 2-mm mesh sieve before mixing them with the amendments. All samples were air-dried at room temperature toa constant mass before being mixed with the amendments.
Twenty grams of air-dried soil (∼ 4 % w w−1 ) was used ineach soil incubation.
2.6 Preparation and properties of amendments
Commercial chicken manure was obtained from the
Tosho Company, Shizuoka Prefecture, Japan, and used as

Table 1 Properties of amendments.
Characteristics

Unit

Total carbon%
Total nitrogen%
C/N ratio
Organic carbon%
pHEC
dS m−1
CaCO3%
Mass water content
%
P2 O5
%
K+
%
2+
Zn
mg kg−1

ChickenmanureChickeneggshell

38.7
3.6
10.7
38.1
8.2
8.5
5
13.3
2.3
2.1
200

16.4
1.9
8.7
4.7
9.9
0.13
97.8
1.7
-

論文：Effects of soil amendments on pH and aggregate stability of saline sodic soil and acid sulfate soil

7

Table 2 Treatments of soil incubation experiment. (LR: lime requirement).
Treatments

Explanation(1) Control(2) COM25(3) COM50(4) CaCO3 − 1/2 LR(5) CaCO3 − LR
(6) COM25 + CaCO3 − 1/2 LR(7) COM50 + CaCO3 − LR

No-amendment
25 g chicken manure kg-soil−1
50 g chicken manure kg-soil−1
50 % LR chicken eggshell
100 % LR chicken eggshell
25 g chicken manure kg-soil−1 + 50 % LR chicken eggshell
50 g chicken manure kg-soil−1 + 100 % LR chicken eggshell

compost. Chicken eggshell substituted for lime because it
contained 97.8 % CaCO3 (Table 1). Eggshells were collected from a canteen in the University of Tokyo. Chicken
manure and eggshell were employed in this study because
they are common wastes in the Mekong Delta region sincepoultry-raising is a popular farm management in the area.
The properties of chicken manure and eggshell are summarized in Table 1. The EC and pH of the chicken manure
were measured using a 1 : 5 solid/water suspension. The
EC and pH of the eggshell were measured using a 1 : 100
solid/water suspension. The CaCO3 content in the chicken
manure and the eggshell was determined from an empiricalstandard curve (Loeppert et al., 1984). The organic carbon
content in the chicken manure and the eggshell were determined using the following formula (Skjemstad and Baldock, 2006):
Organic carbon(%)(%CaCO3 × 12
= total carbon(%) −
100

)
(4)

where %CaCO3 is known percentage of CaCO3 , 12 is molar mass of carbon in CaCO3 (g mol−1 ), 100 is molar massof CaCO3 (g mol−1 ).

experiment was conducted for 45 days at a constant room
temperature (25 ◦ C). A 500 mL glass bottle with two threeway valves on its lid was used. This cap permitted gas
exchange between the outside and inside of the bottle (Dumale et al., 2009). A gas sampling port with an internal
septum was mounted on the lid to collect gas samples inside the bottles (Fig. 2). Before each bottle was sealed
airtight, a 20-g soil sample mixed with amendments wasadded to it. Sufficient water was added to increase soil
moisture to field capacity. Moist air was flushed head spaceof each bottle every two days. In this way, the air in thebottle could be replaced and replenished with outside air
during the incubation periods. Failure to perform this procedure would result in a rapid increase in pressure of CO2(pCO2 ) in the bottles and inhibition of microbial activity.
2.8 Gas sampling and gas analysis
Gas samples were drawn with a 10-mL plastic syringe(Nipro, Osaka, Japan) fitted with a 0.7 × 38.0 mm needle(Nipro, Osaka, Japan) to measure CO2 emission.The gas
samples were then transferred to a 5-mLvacuum glass vial
fitted with a rubber septum. The CO2 concentrations in
2-mL gas samples were measured by gas chromatograph(GC-2014, Shimadzu Corp., Kyoto, Japan).For homoge-

The compost was crushed and passed through a 1-mm
mesh screen. It was applied at rates of 25 and 50 g kgsoil−1 . This can be converted to 25 t ha−1 and 50 t ha−1with an assumption of incorporation into surface 10 cm
thick soil layer and dry bulk density of 1 g cm−3 . Eggshells
were rinsed with tap water and dried in an oven at 105 ◦ C
for 24 h. They were then crushed and passed through a
106-µ m mesh screen. Eggshell-CaCO3 application rates
were based on the results of the lime requirement test
(Sims, 1996). The amounts of CaCO3 required to adjust
the soil pH to 6.5 were set as the lime requirement (LR).
Eggshell-CaCO3 application rates of 50 % and 100 % of
the lime requirement (1/2 LR and LR, respectively) wereused.
2.7 Soil incubation
The incubation experiment consisted of seven treatments
and three replicates as shown in Table 2. The incubation
Fig. 2

Glass bottle used for soil incubation .

土壌の物理性

8neous sampling, a syringe was connected to the three-way
valve to mix the air inside the bottle 4–5 times before sampling. Gas samples were drawn at time zero (to ) of incubation and at the sampling times (ts ) on days 1, 2, 3, 5, 7, 10,
20, 30, and 45 of incubation. The sampling time interval(t) is the difference between ts and to . Since the moist air
was flushed every 2 day, the gas samples at to were collected after flushing and those at ts were collected before
the next flush. The CO2 emission rate was calculated using
the following equation:E=

V × (Cts −Cto ) × M × P × 1000
R × T × 100 × w × t(5)where, E is gas emission rate (mg CO2 g-soil−1 day−1 ),V is volume of bottle (L), Cts and Cto are concentrationof CO2 at ts and to (vol.%), t is sampling time interval
between ts and to (day), M is molar mass of CO2 (44 gmol−1 ), P is air pressure (1 atm), R is gas constant (0.082
L atm K−1 mol−1 ), T is temperature in Kevin (298K), andw is mass of air dry soil (g).

第 141 号

(2019)

ples after the halt of incubation were cut into 2–5 mmpieces. Based on the result of aggregate stability test,
air-dried clods subjected to fast wetting process were employed to evaluate aggregate stability because they suffered
the greatest aggregate deterioration. All samples were airdried at room temperature to a constant weight. Aggregatestability was determined in the same way as for the fast
wetting treatment (Le Bissonnais, 1996).
2.10 Statistical analysis
Means and standard deviations were reported for all
measured parameters. Differences in treatment means
were identified by one-way ANOVA at the 5 % significance level. Two-way ANOVA was used to determine theeffects of the treatments and the moisture conditions on
MWD. Differences between individual means were determined by the least significant difference (LSD) test at the
5 % significance level (LSD0.05 ). A linear regression wasapplied to demonstrate linear correlations between soil pH
and CO2 emission.

3. Results

2.9 Aggregate stability measurement
The field must be plowed to break up the soil blocks
into small fragments before adding the amendments. In
this study, the soil blocks were sieved through a 2-mm
mesh before being mixed with the amendments. During
soil incubation, smaller fragments aggregated into larger,
irregularly shaped blocks. For uniformity, all the soil sam-

Table 3

Soil physico-chemical properties.

Soil types

Unit

pHH2 OECedS m−1
Organic carbon%
Total nitrogen%
C/N ratio
Sand
%
Silt
%
Clay
%
Soil texture
Bulk densityg cm−3
Particle densityg cm−3Porosity%
Moisture at field capacity
m3 m−3Ksat
cm s−1+
Soluble Na (saturation extract)
mmolc L−1
2+
Soluble Ca (saturation extract)
mmolc L−1
Soluble Mg2+ (saturation extract)
mmolc L−1
CEC
cmolc kg−1
SARe(mmolc L−1 )0.5
ESPe%
Lime requirement (LR)g CaCO3 kg-soil−1∗ subscript e denotes values for saturation extract

3.1 Soil properties
The properties of SS, AS, and ASS are shown in Table
3. The soils were clayey. ASS had the highest organiccarbon content (5.7 %) followed by AS and SS (4.1 % and
2.4 %, respectively). Soil pH was lowest in ASS (2.7) andsomewhat higher in AS and SS (4.6 and 5.5, respectively).

Saline-sodic soil (SS) Alluvial soil (AS) Acid sulfate soil (ASS)
5.5
8.2
2.4
0.12
19.3
12.6
35.2
52.2
Clay
1.1
2.8
62.4
0.49
4.4×10−7
69.0
5.1
14.7
42.0
21.9
24.8
3.23

4.6
1.8
4.1
0.24
17.4
16.7
27.8
55.5
Clay
1.1
2.6
59.9
0.41
9.1×10−6
5.1
12.0
12.2
50.1
1.5
2.1
4.89

2.7
8.1
5.7
0.23
25.3
22.1
33.4
44.4
Clay
0.6
2.5
74.9
0.24
1.7×10−2
5.6
6.6
8.0
49.1
2.1
3.0
32.57

論文：Effects of soil amendments on pH and aggregate stability of saline sodic soil and acid sulfate soil

9

Table 4 Effects of initial moisture condition and breakdown processes on mean weight diameter (MWD) (mm) of
three soil types: saline-sodic soil (SS), alluvial soil (AS) and acid sulfate soil (ASS). Initial aggregate size was 2–5 mm
in diameter. Different lower case letters with a row show the significant difference in aggregate stability between initialconditions of soil moisture. Different upper case letters with a column show the significant difference in aggregatestability between breakdown processes at significance level of 5 % using LSD test. P value indicated the probability
for the interaction effect of breakdown processes and initial moisture.

XXX
InitialXXX
XXX moisture
XXX
Breakdown process
X

Saline-sodic soil(SS)

Alluvial soil
(AS)

Acid sulfate soil
(ASS)

Dry

Dry

Dry

Fast wetting
Slow wetting
Mechanical breakdown
Breakdown process × initial moisture

1.91aA
2.67bBaB
2.70
2.68aB
aB
2.57
2.55aAP = 9.31 × 10−5

Moist

Moist

2.37aA
2.69bBbC
2.74
2.70aBaB
2.59
2.50aAP = 8.6 × 10−7

Moist

2.36aA
2.68bBaB
2.65
2.71aBbB
2.65
2.58aAP = 0.00043

Table 5 Effects of initially dry clod sizes on fragment size distribution under the fast wetting
process. “d” expressed fragment size. Different letters show the significant difference at significance level of 5 % using LSD test .
Soils

Saline-sodic
soil (SS)d > 2 mm

1– 3 mm
2– 5 mm
5–10 mm21.61a43.63b
48.06b
14.71
0.01

58.24a46.96a47.03a16.87
0.25

20.15c
9.41b
4.91a
3.36
8.53 × 10−5

1– 3 mm
2– 5 mm
5–10 mm48.48a77.85b
68.99b
12.37
0.003

41.79b
20.56a26.76a11.44
0.01

11.14b
2.43a
4.25a
6.22
0.03

1– 3 mm
2– 5 mm
5–10 mm

74.61a79.70a87.50b
7.69
0.04

15.38ab16.92b
9.70a
6.51
0.08

10.01b
4.04a
2.80a
2.79
0.002

LSD0.05
P
Alluvial soil(AS)
LSD0.05
P
Acid sulfate
soil (ASS)
LSD0.05
P

Percentage of size fractions (%)
0.25 mm < d < 2 mm d < 0.25 mm

Initial clod sizes

Even the pH of SS was not optimum for plant growth, SS
had high sodicity (ESP = 24.8 %) and high salinity (ECe
= 8.2 dS m−1 ). ESP for ASS and AS was only 3.0 % and
2.1 %, respectively. ECe was high for ASS and low for AS(8.1 dS m−1 and 1.8 dS m−1 , respectively). Since the pH of
ASS was very low (2.7), it could have soluble Al (Tho andEgashira, 1976; Naramabuye and Haynes, 2006b; Khoi etal., 2010; Strawn et al., 2015) and soluble Fe (Stefansson,
2007; Strawn et al., 2015). In contrast, since the pH of AS
was 4.6, it probably had relatively less soluble Al and Fe(Strawn et al., 2015). Other soil properties are summarizedin Table 3.

3.2.1 Effects of initial soil moisture and breakdown processes on aggregate stability

3.2 Effects of initial soil moisture, breakdown
processes and clod sizes on soil aggregate stability

Table 5 shows the fragment size distribution of dry clods
after the fast wetting process for the three different initial
sizes. After fast wetting, the portion of fragments > 2 mm

The effects of initial soil moisture and breakdown processes on aggregate stability of 2–5 mm clods are shownin Table 4. The MWDs of the dry clods under fast wetting
were lower than those under slow wetting and mechanical breakdown, and the differences were significant (P <0.01). Under fast wetting, the MWDs were lower for dry
clods than moist clods, and the differences were significant(P < 0.05). Moist clods were less stable under mechanicalbreakdown than the slow and fast wetting treatments.
3.2.2 Effects of clod sizes on aggregate stability

10

土壌の物理性

第 141 号

(2019)

pH. Compost raised the pH of ASS to be 2.6 and 2.4
when it was applied at 25 and 50 g kg-soil−1 , respectively.
The combination of CaCO3 and compost increased soil pH
more than either CaCO3 or compost application. The combination raised soil pH to be 6.5, 6.7, and 3.9 in SS, AS,
and ASS, respectively, at the rate of 1/2 LR CaCO3 and 25
g compost g-soil−1 . The combined application at rates of
CaCO3 (LR) and compost (50 g kg-soil−1 ) could raise soil
pH to be 7.2, 7.1, and 5.8 for SS, AS, and ASS, respectively.

Fig. 3 Effects of compost and calcium carbonate application
on pH of the soils after 45 days soil incubation. Vertical error bars show the standard deviation. Different letters show
the significant differences between treatments at significancelevel of 5 % using LSD test: saline-sodic soil (SS) (LSD0.05 :0.21; P = 4.3 × 10−12 ); alluvial soil (AS) (LSD0.05 = 0.33;
P = 2.2 × 10−8 ) and acid sulfate soil (ASS) (LSD0.05 = 0.39;
P = 2.9 × 10−11 ). “COM” and “LR” refer to Table 2 and Table
3, respectively.

was significantly (P < 0.01) greater for the 2–5 mm and the
5–10 mm clod group than for the 1–3 mm clod group. In
contrast, the portion of fragments < 0.25 mm for the 1–3
mm size clods was twice of that of the two larger clod sizegroups. Dry clods of ASS showed that all three size groups
had high portions of fragments > 2 mm. In ASS, the proportion of fragments > 2 mm increased with increasing initial clod sizes. The dry clods of 2–5 mm and 5–10 mm insize were more durable under fast wetting (Mekong Delta
squall) than those 1–3 mm in diameter.
3.3 Effects of chicken manure-compost andeggshell-CaCO3 application on soil improvement
3.3.1 Effects of compost and eggshell-CaCO3
application on soil pH
Changes in soil pH after 45 days soil incubation with orwithout amendments are presented in Fig. 3. In this study,
the initial soil pH was relatively low (2.7 in ASS, 4.6 in
AS, and 5.5 in SS (Table 3)). After 45 days incubation, thepH of unamended ASS and SS decreased to 1.9 and 4.4, respectively whereas that of unamended AS rose slightly to
4.9. The pH of the amended soils was significantly higher(P < 0.001) than the unamended soils. When eggshellCaCO3 application increased from 1/2 LR to LR, the soil
pH increased from 5.6 to 6.0 in SS, from 5.8 to 6.6 in AS,
and from 3.5 to 4.9 in ASS. By definition, the lime requirement (LR) is the amount of calcium carbonate required toraise the soil pH to be 6.5. However, the pH of ASS and
SS after 45 days incubation was lower than this value.
Compost substantially increased soil pH from 5.8 to 6.5
in SS and from 5.8 to 6.2 in AS when the amount of compost increased from 25 g kg-soil−1 to 50 g kg-soil−1 . In
ASS, the compost was less effective for increasing soil

3.3.2 Effects of compost and eggshell-CaCO3
application on soil aggregate stability
MWD of the soils after 45 days incubation with or without amendments are shown in Table 6. The MWDs of theunamended soils and the soils amended with CaCO3 alone
were significantly (P < 0.001) smaller than those of thesoils amended with either compost or compost combinedwith CaCO3 . In SS, aggregate breakdown after CaCO3 -LR
application was greater than that observed after the application of CaCO3 -1/2 LR. In AS and ASS, there was no
significant difference in MWDs between the two CaCO3
doses. CaCO3 application increased soil pH and thus could
enhance clay dispersion by increasing negative charges on
the clay particles (Roth and Pavan, 1991).
Compost application significantly (P < 0.001) increased
MWDs for all the soils. Increasing compost from 25 g kgsoil−1 to 50 g kg-soil−1 significantly (P < 0.001) increased
MWD from 2.32 mm to 2.53 mm and from 2.39 mm to2.62 mm for SS and AS, respectively. The aggregate stability of ASS also increased significantly (P < 0.001) when
compost was applied. Nevertheless, there was no significant difference in MWD for ASS between the two compost doses. The relatively higher MWDs of the three soils
amended with combinations of compost and CaCO3 indicated that the combined application of CaCO3 and compost
increased soil aggregate stability. Compost decomposition
may have induced the production of microbial metabolites
which enhanced aggregate stability (Carrizo et al., 2015).
3.3.3 Effects of compost and eggshell-CaCO3
application on CO2 emission
The total CO2 emissions from the soils with or without
the amendments after 45 days of incubation are shown in
Fig. 4. Without the amendment, all the soils had low CO2
emission levels (< 0.8 mg CO2 -C g-soil−1 ). It was the initial soil pH rather than the soil organic carbon content responsible for the low CO2 emission rates in the unamended
soils. CaCO3 application increased soil pH and, by extension, total CO2 -C evolution. CaCO3 application significantly increased (P < 0.001) CO2 emission for 45 days. In
SS, the total CO2 emission was 1.42 mg CO2 -C g-soil−1
at the lower CaCO3 dose (1/2 LR) and 2.12 mg CO2 -C gsoil−1 at the higher CaCO3 dose (LR). In AS, the total CO2

論文：Effects of soil amendments on pH and aggregate stability of saline sodic soil and acid sulfate soil

emission was 2.01 mg CO2 -C g-soil−1 and 2.92 mg CO2 C g-soil−1 at the CaCO3 application rate of 1/2 LR andLR, respectively. The total CO2 emitted in response to the
CaCO3 treatment was highest for ASS. This soil had total
CO2 emission of 7.47 mg CO2 -C g-soil−1 and 11.42 mg
CO2 -C g-soil−1 at the 1/2 LR and LR doses, respectively.
Compost application enhanced total CO2 emission during the 45 days incubation (Fig. 4). There was a significant difference (P < 0.001) in total CO2 emission between
compost-amended soils and unamended soils. The total
CO2 emission increased significantly (P < 0.001) with increase in compost application rate. In compost-amended
SS, the total CO2 emission was 6.87 and 12.76 mg CO2 C g-soil−1 at the compost application rate of 25 and 50 g
kg-soil−1 , respectively. In compost-amended AS, the total
CO2 emission was 7.66 and 14.66 mg CO2 -C g-soil−1 atthe compost application rate of 25 and 50 g kg-soil−1 , respectively. However, the total CO2 emission of compostamended ASS was lower than those of the other soils.
Compost application rates of 25 and 50 g kg-soil−1 resulted in CO2 emission of 3.54 and 4.29 mg CO2 -C gsoil−1 , respectively. The extremely low pH of ASS could
restrict microbiological activity and could account for low
CO2 emission.
Fig. 4 indicates that the soils amended with both
eggshell-CaCO3 and compost emitted more CO2 thanthose treated with either CaCO3 or compost alone. The
total CO2 emitted from SS amended with a combination of
CaCO3 (1/2 LR) and compost (25 g kg-soil−1 ) was 7.99
mg CO2 -C g-soil−1 , which was higher than that for SS
treated with either CaCO3 or compost. The highest total
CO2 emission (14.11 mg CO2 -C g-soil−1 ) was recorded
for SS treated with the combination of CaCO3 (LR) andcompost (50 g kg-soil−1 ). The total CO2 emission for SS
amended with CaCO3 (LR) alone and compost (50 g kg-

soil−1 ) alone was 2.12 and 12.76 mg CO2 -C g-soil−1 , respectively. For AS, the total CO2 emission was also thehighest for the combination of CaCO3 and compost. In
ASS, the total CO2 emission from the soil amended with
CaCO3 and compost combination was 10.94 and 16.84 mg
CO2 -C g-soil−1 for the CaCO3 -1/2 LR and 25 g compost
kg-soil−1 , and the CaCO3 -LR and 50 g compost kg-soil−1
treatments, respectively. The differences in CO2 emission between the compost and CaCO3 combination andthe compost application alone were small for SS and AS.
On the other hand, the differences in CO2 emission between the compost and CaCO3 combination and the compost alone were significantly large for ASS. The increasein soil pH (Fig. 3) by the combined application of compost
and CaCO3 could enhance soil CO2 emission (Fig. 4).

Fig. 4 Total CO2 emission from compost and calcium carbonate application during 45 days soil incubation. Vertical error bars show standard deviation. Different letters show significant differences between treatments at the significance levelof 5 % using LSD test: saline-sodic soil (SS) (LSD0.05 =0.24; P = 1.9 × 10−22 ), alluvial soil (AS) (LSD0.05 = 0.16;
P = 1.6 × 10−25 ) and acid sulfate soil (ASS) (LSD0.05 = 0.52;
P = 9.6 × 10−18 ). “COM” and “LR” refer to Table 2 and Table
3, respectively.

Table 6 Effects of amounts of calcium carbonate and compost application on mean weight diameter (MWD)(mm) of soils after 45 days incubation. Aggregate analysis has been conducted on air dry soil having 2–5 mm indiameter. Aggregate analysis employed the fast wetting process. Different letters show significant differences
between treatments at significance level of 5 % using LSD test. Mean ± standard deviation is shown in thesame treatment of the same soil. “COM” and “LR” refer to Table 2 and Table 3, respectively.
Treatments
Control
CaCO3 -1/2 LR
CaCO3 -LR
COM25
COM50
COM25 + CaCO3 − 1/2 LR
COM50 + CaCO3 − LR
LSD0.05
P

Saline-sodic soil (SS)
0.57a ± 0.04
0.94 ± 0.13
0.59 ± 0.08
2.32cd ± 0.10
2.53e ± 0.05
2.25c ± 0.07
2.49de ± 0.04
0.169
1.04 × 10−13

11Alluvial soil (AS)0.77a ± 0.08
0.93a ± 0.08
0.79a ± 0.06
2.39b ± 0.09
2.62c ± 0.02
2.39b ± 0.14
2.51bc ± 0.08
0.183
5.9 × 10−13

Acid sulfate soil (ASS)
1.22b ± 0.07
0.78a ± 0.10
1.08ab ± 0.28
1.96c ± 0.09
1.99c ± 0.14
2.22c ± 0.14
2.20c ± 0.14
0.324
2.8 × 10−7

12土壌の物理性

第 141 号

(2019)

ASS, low CO2 emission rates were recorded for the first 3
days after compost application (< 0.3 mg CO2 -C g-soil−1
day−1 ). The CO2 emission rate started to increase at the
5th day (0.88 mg CO2 -C g-soil−1 day−1 ) and rose to 1.09
mg CO2 -C g-soil−1 day−1 by day 7. Thereafter, the CO2
emission rates gradually declined until the 20th day.
The daily CO2 emission rates of SS and AS amended
with compost and CaCO3 combination during 45 days soil
incubation resembled to those obtained for SS and AS
treated with compost alone (Fig. 5). The maximum CO2
emission rate was recorded at 3rd day (3.78 and 3.84 mg
CO2 -C g-soil−1 day−1 for SS and AS, respectively). For
ASS, the daily CO2 emission rate with the amendment
combination was similar to those obtained with CaCO3
alone within the first 2 days. The CO2 emission rate thenrose to be maximal, with 1.94 mg CO2 -C g-soil−1 day−1by day 7. The rapid increase and decrease in daily CO2emission rate within the first 2 days may have been caused
by CaCO3 reactions. The subsequent increase in daily CO2emission rate between day 5 and day 20 could be explainedby the microbial activity in compost disintegration.

4. Discussion
4.1 Effect of eggshell-CaCO3 and compost
application on soil pH

Temporal changes in daily CO2 emission rates during
45 days soil incubation are shown in Fig. 5. ASS witheggshell-CaCO3 application showed the maximum CO2
emission rate of 5.83 mg CO2 -C g-soil−1 day−1 at thefirst day after the application. For SS and AS, CO2 emission also rose rapidly in the first day after CaCO3 application (0.86 and 1.28 mg CO2 -C g-soil−1 day−1 for SS and
AS, respectively) but its CO2 emission rate was lower thanthat of ASS. The CO2 emission rates abruptly ascended
then descended for all three soils over the first 2 days after
CaCO3 application.

CaCO3 is commonly used to alleviate low pH soils. After CaCO3 application, pH of the soils was significantly
improved (Fig. 3). The CaCO3 application at the rate oflime requirement (LR) expected to raise the soil pH to be
6.5. However, the pH of SS and ASS remained < 6.5 after 45 days incubation. While the pH of SS was raised
to be 6.0 by the eggshell-CaCO3 application at the rateof LR, the pH of ASS was raised to be 4.9. A possible explanation for low pH of ASS is gradual oxidationof pyrite, which was not considered when lime requirement test was conducted. In pyrite oxidation process, sulfuric acid (H2 SO4 ) is produced and lowers pH of ASS(Attanandana and Vacharotayan, 1986). As Jayalath et al.
(2016) suggested that pyrite oxidation process might continue over 70 days incubation. Besides, in lime requirement test, pH of the soil with CaCO3 was evaluated after
24 hours incubation, and the pH of the soil with eggshellCaCO3 at the rate of LR was measured after 45 days incubation.

After compost application, the CO2 emission rates
rapidly increased for SS and AS over the first 5 days (Fig.
5). The highest CO2 emission rate was observed at the
3rd day after compost application (4.35 and 5.04 mg CO2 C g-soil−1 day−1 for SS and AS, respectively). Gradualdeclines in CO2 emission rate occurred from the 5th day
to the 20th day after amendment application. However, inApplication of compost could also raise soil pH. There
were substantial rises in the pH of both SS and AS when
the compost application rates increased from 25 g kgsoil−1 to 50 g kg-soil−1 (Fig. 3). On the other hand, thepH of ASS rose less in response to compost application.
The addition of 50 g compost kg-soil−1 increased the pH
of ASS from 1.9 as control treatment to 2.4. The CaCO3

Fig. 5 Effect of calcium carbonate and compost on daily
CO2 emission rate during 45 days incubation: (a) salinesodic soil (SS), (b) alluvial soil (AS) and (c) acid sulfate soil
(ASS). Vertical error bars show standard deviation. “COM”
and “LR” refer to Table 2 and Table 3, respectively.

論文：Effects of soil amendments on pH and aggregate stability of saline sodic soil and acid sulfate soil

13

ter complexes could not affect the pH of ASS after compost
application.

Fig. 6 Correlation between soil pH and CO2 emission after
application of compost with or without CaCO3 , where CO2
emission from CaCO3 was subtracted. The soil incubation was
conducted at 25 ◦ C, moisture at field capacity for 45 days.

in the chicken manure compost might contribute to raisesoil pH. In this study, the chicken manure contained 5 %CaCO3 (Table 1). The application of 25 and 50 g chicken
manure kg-soil−1 equaled the 1.25 and 2.5 g CaCO3 kgsoil−1 through chicken manure application. The eggshellCaCO3 application at the rate of 1/2 LR and LR corresponded to 1.6 and 3.2 g CaCO3 kg-soil−1 , respectively in
SS and 2.45 and 4.9 g CaCO3 kg-soil−1 , respectively in
AS. The amount of CaCO3 in the applied chicken manure
at the rates of 25 and 50 g kg-soil−1 could help to rise pH of
SS. Similar pH of AS was shown between the 25 g chicken
manure kg-soil−1 and 1/2 LR CaCO3 although amount of
CaCO3 in the application rate of 25 g chicken manure kgsoil−1 was less a half than the amount of CaCO3 at rateof 10/2 LR. This suggested alternative process other than
the reaction of CaCO3 was responsible for rise in pH of
AS. In ASS, the eggshell-CaCO3 application at the 1/2 LR
and LR corresponded to 16.3 and 32.6 g CaCO3 kg-soil−1 ,respectively. The amount of CaCO3 in applied chicken
manure was minor and negligible. Therefore, CaCO3 inchicken manure could contribute less on the rise in pH of
ASS.
Aluminum-organic matter complexes are also expected
to raise soil pH after compost addition (Naramabuye andHaynes, 2006a; Hue and Amien, 1989). Hydrolysis of soluble Al species may depress soil pH (Strawn et al., 2015),
and Al-organic matter complexes depress soluble Al concentration. AS which had the initial pH of 4.6 may contain
Al(OH)2+ and Al3+ as Al species. Following to the application of organic matter, the rise in pH might be caused by
Al-organic matter complexes (Naramabuye and Haynes,
2006a). In SS, since the initial pH was 5.5, it could containan abundance of insoluble Al which may not complex withthe organic matter. In contrast, ASS which had an original pH of 2.7 or less may have high concentrations of Al3+
(Khoi el al., 2010). Increase in the compost application did
not increase the pH of ASS suggesting that Al-organic mat-During compost decomposition by micro-organisms, hydron consumption by soluble organic anions in decarboxylation processes is expected to rise in soil pH (Yan et al.,
1996; Naramabuye and Haynes, 2006b). Yan et al. (1996)
used malate and citrate to discuss the role of biological decarboxylation of soluble organic anions on soil pH. They
concluded that in aerobic conditions, neither denitrification
nor reduction of Mn and Fe was responsible for soil pH
rise. Naramabuye and Haynes (2006b) suggested that the
decarboxylation of organic anions raised pH during manure decomposition. The biological decarboxylation ofsoluble organic anions may account for the rise in pH in
addition to being a source of CO2 . In the decarboxylation
process, hydron (H+ ) is consumed by organic anions andreleases CO2 as the following equation:
R − CO − COO− + H+ → R − CHO + CO2(6)This process simultaneously raises soil pH and produces
CO2 . Fig. 6 shows positive linear relationships (r = 0.83
for SS and AS, r = 0.82 for ASS) between soil pH and
CO2 emission for 45 days incubation with either compost or compost with eggshell-CaCO3 . In this figure, CO2
emission was derived by subtracting CO2 emission of the
CaCO3 applied soil from the total CO2 emissions. It represents CO2 emission from organic matter decomposition
by microbiologies. Although quantitative discussion of
pH and CO2 production relationship requires soil buffering characteristic (Yan et al., 1996), the rise in both pH
and CO2 emission (Fig. 6) qualitatively suggested that therise in soil pH following compost application was caused
by decomposition of compost and subsequent decarboxylation (Yan et al., 1996). At least in the present study, bothsoil pH and CO2 emission increased after adding either
compost or compost with eggshell-CaCO3 (Fig. 6).
4.2 Effect of eggshell-CaCO3 and compost application on CO2 emission
CaCO3 application increased CO2 emission rates. Rapid
increase in CO2 emission rates for all the soils occurred
within the first 2 days after the CaCO3 adding (Fig. 5). It
could be a reaction between CaCO3 and hydron in the soil
solution. Dumale et al. (2011) reported a rapid increase in
CO2 -C evolution within 2 days after CaCO3 application in
an Ultisol. They suggested that the CaCO3 was promptly
solubilized in low-pH soils like Ultisols. In this study, themaximum CO2 emission rate was found at first day after
CaCO3 amendment followed by an abrupt decline thereafter. For the soils amended with CaCO3 , the CO2 emission rates were high in ASS and low in both SS and AS.
The differences in the initial soil pH may account for the14

土壌の物理性differences in CO2 emission rates among the soils following CaCO3 application. In the present study, ASS had thelowest pH (Table 3). Much hydron in ASS reacted with theapplied CaCO3 , and released CO2 much faster than SS and
AS whose pH was comparatively higher.
Changes in CO2 emission rates suggested that the soils
with compost had higher microbiological activity, andthus, higher CO2 emission rates. However, the CO2 emission rates in response to compost application varied among
soil types. A substantial increase in CO2 emission rate occurred within the first 5 days in compost-amended SS andAS (Fig. 5a and 5b). In ASS, a gradual rise in CO2 emission rate began on day 5 and continued until day 20 (Fig.
5c). The changes in CO2 emission in the latter stage ofincubation after compost application relied to the activityof micro-organisms. The extremely low pH of ASS could
inhibit microbiological activity. A suitable pH range formicrobial growth is 5-7 (Pietri and Brookes, 2008). AS
and SS with compost application had relatively higher initial pH and showed quick increase in CO2 emission rate in
the early stage of incubation (Fig. 5a and 5b). In contrast,
extremely acidic ASS could have limited microbial activity and gradually increased CO2 emission rates in the latterstage of soil incubation with compost application (Fig. 5c).
There were similar trends of CO2 emission rates of SS
and AS in response to compost application and combination of compost and CaCO3 application (Fig. 5a and 5b).
For both AS and SS, the CO2 emission rates increased
within the first 5 days after application of either compost or
combination of compost and CaCO3 . In case of the CaCO3
application alone, there was a small increase in CO2 emission rate induced by CaCO3 reactions within the first 2
days. Therefore, CO2 emission rate of AS and SS proceeded more than 2 days after the combined application ofcompost and CaCO3 could be responsible for an increasein microbial decomposition activity (Fig. 5a and 5b). In
strongly acidic ASS, there were similar temporal changes
in CO2 emission rate within the first 2 days after CaCO3
application and the combined application of compost andCaCO3 . The second increase in CO2 emission rate between day 5 and day 20 in response to the application of
the combination of compost and CaCO3 was twice of thatfor the compost alone (Fig. 5c). This second rise in CO2emission rate could be the result of the enhancement of microbial activity. It implied that the rise in pH induced by
CaCO3 in combination with compost could produce more
CO2 by microbiological activity in compost decompositionin the latter stage of incubation. It showed that the combined application of eggshell-CaCO3 and compost could
increase soil CO2 emission rate more than either eggshellCaCO3 or compost alone. The rise in soil pH caused by
the application of compost and CaCO3 (Fig. 3) could en-

第 141 号

(2019)

hance soil CO2 production (Fig. 4). Condron et al. (1993)
reported that soil CO2 respiration in acid soils (pH 4.43)
with addition of lime and litter was much more than thatwith addition of either lime or litter for 17 weeks of incubation. However, Condron et al. (1993) showed weekly CO2emission which was from the first week to the 17th week.
As Dumale et al. (2011) suggested that CO2 emission following lime application occurred within a few days. Thus,
weekly CO2 emission rate cannot separate sources of CO2 ,i.e. CaCO3 and organic matter. In the present study, therapid increase in daily CO2 emission rate occurred within
the first two days. It was due to eggshell-CaCO3 reaction.
CO2 emission proceeded more than 2 days and later wasfrom chicken manure compost decomposition by microbiological activity. Xue et al. (2010) reported an increasein soil microbiological population following the additionof CaCO3 to acidic tea orchard soils. Pietri and Brookes(2008) stated that soil CO2 evolution from microbiologicalactivity increased with pH. The relatively higher CO2 evolution rates from the combined application of CaCO3 andcompost suggested that CaCO3 in the combination could
be highly effective at promoting microbiological activity
in very acidic soils.
4.3 Effect of eggshell-CaCO3 and compost application on aggregate stability
Tillage is conducted to prepare the seedbed to support
seedling germination and plant growth. Aggregate stability
is influenced by the clod size produced by tillage. Under
fast wetting condition, dry clods 2–5 mm and 5–10 mmin size were more durable than those 1–3 mm in diameter (Table 5). Dry clods subjecting to fast wetting process
were less stable in the three soils. In tropical areas like
Mekong Delta region, dry soils are exposed to prolonged
sunny days. Furrow irrigation, border irrigation or heavy
rainfall may cause fast wetting. In the present study, this
scenario was simulated by dry clods subjecting to fast wetting process. Fast wetting of air-dried 2–5 mm clods was
employed to assess aggregate stability after incubation of
the soils with the amendments.
The smaller MWDs of the unamended soils and thoseamended with eggshell-CaCO3 showed aggregate deterioration. According to Roth and Pavan (1991), liming increased soil pH and enhanced clay dispersion by increasing negative charges of clay particles. The amounts of applied CaCO3 used in this study did not significantly affect MWD. Higher MWDs were observed in soils addedwith compost and combinations of compost and eggshellCaCO3 . The aggregate stability of AS and SS was statistically greater at the higher amendment dose than thelower dose. The aggregate stability of ASS significantly increased with the addition of compost. Nevertheless, there
was no significant difference in MWD of ASS between the論文：Effects of soil amendments on pH and aggregate stability of saline sodic soil and acid sulfate soil

two compost doses. The increase in MWD in response tocompost amendment implied that compost played an important role in stabilizing soil aggregates. Organic amendments may help stabilize aggregates by inducing microbiological decomposition of organic matter (Griffiths andJones, 1965). Organic products from the microbiological decomposition of organic residues may act as binding
agents and enhance aggregate stability by resisting the effects of slaking under fast wetting (Carrizo et al., 2015).
Earlier studies have discussed the roles of organic binding
agents, clay-polyvalent cations-organic matter, and clayorganic matter in stabilizing aggregates against slaking andclay dispersion in soils (Tisdall and Oades, 1982; Nelson
and Oades, 1998). In this study, chicken manure was used
as a compost. It is an easily decomposable organic carbon source with a low C/N ratio (Table 1). The organic
compounds released by decomposing process may bindsoil particles and enhance aggregation. The amendment
consisting of compost and CaCO3 was highly effective atincreasing pH and stabilizing the aggregates of the threesoils.

5. Conclusions
In the results of the aggregate stability test, mean weight
diameter (MWDs) was the lowest for dry clods subjected
to fast wetting. MWDs also suggested that saline sodic
soil (SS) had the most fragile aggregates, followed by alluvial soil (AS) and acid sulfate soil (ASS). In the actual
field, surface soils become dry when they are exposed toprolonged sunny days. Substantially lower MWD suggests
heavy rainfall events or abrupt irrigation on dry soil surfaces may degrade aggregates.
In the Mekong Delta region, there is a great deal of interest in soil pH amelioration. CaCO3 is commonly used
to raise soil pH. The pH of SS and AS was improved byadding either CaCO3 or compost or both. The only exception was for compost-amended ASS, where compost
application could not raise pH. Only eggshell-CaCO3 or
eggshell-CaCO3 with compost was effective to raise pH of
ASS. Improving soil pH as well as aggregate stability isdesirable to intensify soil productivity. The present study
showed that although the physicochemical properties of
the three soils differed, their aggregates deteriorated witheggshell-CaCO3 application while soils amended with either chicken manure compost or chicken manure compost
with eggshell-CaCO3 presented greater aggregate stability. Relationships between soil pH and CO2 emission fromcompost applied soils suggested that microbiological activity was affected by soil pH. Upon compost application
to the three soils, CO2 emission was more in SS and AS
that had slightly low pH than ASS that had extremely low

15

pH. In slightly acidic soils like SS and AS, the highest
CO2 emission rates were measured within the first 5 days
after compost application, while ASS took more time toshow peak CO2 emission rate. The combination of compost and CaCO3 increased soil pH and CO2 emission in
all three soils. This suggested that microbiological activity
was enhanced by an increase in soil pH by CaCO3 in combination of chicken manure compost and eggshell-CaCO3 .
The rise in soil pH induced by the CaCO3 in the compostand eggshell-CaCO3 combination could create a suitableenvironment for microorganism growth and promote compost decomposition. The organic by-products of microbial
compost decomposition may enhance aggregate stability.
The results of this study indicated that the combinationof eggshell-CaCO3 and chicken manure compost that arecommon agricultural wastes in Mekong delta region improved soil pH and sustain aggregate stability. This information may help farmers to improve quality of low pH
soils.

Acknowledgments
This study was partly supported by Kakenhi(15H02467). The author would like to express sincerely thanks Japanese Government who supported
MEXT scholarship for PhD research. Many sincerely
thanks would like to send Mr. Hiromi Imoto because of his
enthusiastic helps to fulfill experiments. The authors thankto all members of the Laboratory of Soil Physics and Soil
Hydrology, Department of Biological and Environmental
Engineering of the University of Tokyo for their assistancein soil sampling.

References
Abu-Sharar, T.M., Bingham, F.T. and Rhoades, J.D. (1987): Stability of soil aggregates as affected by electrolyte concentration and composition. Soil Sci. Soc. Am. J., 51: 309–314.
Almajmaie, A., Hardie, M., Acuna, T. and Birch, C. (2017): Evaluation of methods for determining soil aggregate stability. Soiland Tillage Res., 167: 39–45.
Arai, M., Keren, R., Yamamoto, T. and Inoue, M. (2003): Aggregate stability evaluation of sodic soils using ethanol-water
mixtures. Trans. of Japan. Soc. of Irrigation Drainage andReclamation Engineering, 224: 65–71.
Attanandana, T. and Vacharotayan, S. (1986): Acid sulfate soils:
Their characteristics, genesis, amelioration and utilization.
Southeast Asian Studies, 24 (2): 154–180.
Blake, G.R. and Hartge, K.H. (1986): Particle density. In Klute
A. (ed.) Methods of Soil Analysis. Part 1. Physical and Mineralogical Methods. Second edition. SSSA Book Series No 5.
pp. 377–382. SSSA and ASA, Madison, WI, USA.

16

土壌の物理性Braunack, M.V. and Dexter, A.R. (1988): The effect of aggregate

第 141 号

(2019)

size in the seedbed on surface crusting and growth and yield

Linear Extensibility, In: Dane, J. H. and Topp, G. C. (Ed.)
Methods of Soil Analysis: Part 4: Physical Methods. SSSA

of wheat (Triticum aestivum L., cv. Halberd)., Soil and Tillage

Book Series No5, pp. 205–228, SSSA and ASA, Madison, WI,

Res., 11(2): 133–145.

USA.

Carrizo, M.E., Alesso, C.A., Cosentino, D. and Imhoff, S. (2015):

Hue, N.V. and Amien, I. (1989): Aluminum detoxification with

Aggregation agents and structural stability in soils with dif-green manures. Commun. Soil. Sci. Plant. Anal., 20: 1499–

ferent texture and organic carbon contents. Sci. Agric., 72(1):75–82.
Chaganti, V.N., Crohn, D.M. and Simunek, D.C. (2015): Leaching and reclamation of a biochar and compost amended salinesodic soil with moderate SAR reclaimed water. Agricultural
Water Management, 158: 255–265.
Condron, L.M., Tiessen, H., Trasa-Cepeda, C., Moir. J.O. and

1511.
ISSS/ISRIC/FAO (1998): World Reference Base for Soil Resources. World Soil Reference Report No. 84. FAO, Rome.
1–96.
Iqbal, M.T. (2012): Effect of Al compounds on soil pH andbioavailability of Al in two acid soils. Research Article. Turk.
J. Agric. For., 36: 720–728.

Stewart, J.W.B. (1993): Effects of liming on organic matter

Jayalath, N., Mosley, L.M., Fitzpatrick, F.W. and Marschner, P.

decomposition and phosphorus extractability in an acid humic(2016): Addition of organic matter influences pH changes in

Ranker soil from Northwest Spain. Biol. Fertil. of Soils, 15:

reduced and oxidized acid sulfate soils. Geoderma, 262: 125–279–284.

132.

Dikinya, O. and Mufwanzala, N. (2010): Chicken manure-

Karcauskiene, D., Jokubauskaite, I., Repsiene, R., Ambrazaitiene,

enhanced soil fertility and productivity: Effects of application

D. and Slepetiene, A. (2015): Effect of liming on the dynam-

rates. J. of Soil Science and Environmental Management, 13:

ics of water stable aggregates and organic carbon in Moraine

46–54.

Loam soil. NJF 25th Congress Nordic View to Sustainable Ru-

Duc, H.Q. and Dao, N.V. (2011): Evaluating the changes of salineral Development. Soil and Water Management, 195–200.

soils and acid sulfate soils in the Cuu Long River Delta after 30

Kemper, W.D. and Rosenau, R.C. (1984): Soil cohesion as af-

years of using. J. Sci. Technol. Agric. Viet Nam, 1(22): 1–7.

fected by time and water content. Soil Sci. Soc. Am. J., 48(5):Dumale, W.A., Miyazaki, T., Nishimura, T. and Seki, K. (2009):

1001–1006.

CO2 evolution and short-term carbon turnover in stable soil

Khoi, C.M., Guong, V.T., Trung, P.N.M. and Nilsson, S.I. (2010):

organic carbon from soils applied with fresh organic matter.

Effects of compost and lime amendment on soil acidity and N

Geophysical Research Letters, 36: 1–6.

availability in acid sulfate soil. 19th World Congress of Soil

Dumale, W.A., Miyazaki, T., Hirai, K. and Nishimura, T. (2011):

Science, Brisbane, Australia. Published on DVD, pp. 52–55.

SOC turnover and lime-CO2 evolution during liming of anKlute, A. (1986): Water retention: Laboratory methods. In: Klute,acid Andisol and Ultisol. Open Journal of Soil Sci., 1: 49–53.

A., (Ed.), Methods of Soil Analysis, Part 1: Physical and Min-

Emerson, W.W. (1957): Organo-clay complexes. Nature, 180: 48–

eralogical Methods, SSSA Book Series No.5, pp. 635–662.

49.

SSSA and ASA, Madison, WI, USA.

Farahani, E., Emami, H., Keller, T., Fotovat, A. and Khorassani,

Klute, A. and Dirksen, C. (1986): Hydraulic conductivity andR. (2018): Impact of monovalent cations on soil structure. Part

diffusivity: laboratory methods. In: Klute A. (Ed.) Methods

I. Results of an Iranian soil. Int. Agrophys., 32: 57–67.

of Soil Analysis. Part 1: Physical and Mineralogical Methods.

Frenkel, H., Goertzen, J.O. and Rhoades, J.D. (1978): Effects ofSoil Sci. Soc. of Am. Book Series. No. 5, pp. 687–734. SSSA

clay type and content, exchangeable sodium percentage, andelectrolyte concentration on clay dispersion and soil hydraulicconductivity. Soil Sci. Soc. Am. J., 42: 32–39.
Gapon, Y.N. (1933): On the theory of exchange adsorption in

and ASA, Madison, WI, USA.
Le Bissonnais Y. (1996): Aggregate stability and assessment ofsoil crustability and erodibility: I Theory and methodology.
Eur. J. Soil Sci., 47: 425–437.

soils. J. Gen. Chem. USSR (Engl. Transl.), 3: 144–160.

Legout, C., Leguedois, S. and Le Bissonnais, Y. (2005): Aggre-

Gee, G.W. and Bauder, J.W. (1986): Particle size analysis. In

gate breakdown dynamics under rainfall compared with aggre-

Klute A. (ed.) Methods of Soil Analysis. Part 1. Physical andgate stability measurements. Eur. J. of Soil Sci., 56: 225–237.

Mineralogical Methods. Second edition, pp. 383–412. SSSA

Loeppert, R.H., Hallmark, C.T. and Koshy, M.M. (1984): RoutineBook Series No.5, SSSA and ASA, Madison, WI, USA.
General Statistics Office of Vietnam (2015): Statistical year bookof Viet Nam.

procedure for rapid determination of soil carbonates. Soil Sci.
Soc. Am. J., 48: 1030–1033.
McLean, E.O. (1982): Soil pH and lime requirement. In PageA.

Griffiths, E. and Jones, D. (1965): Microbiological aspects of soilL., et al. (ed.) Methods of soil analysis: Part 2. Chemical andstructure. I. Relationships between organic amendments, mi-microbiological methods. 2nd ed. Agronomy monograph 9,

crobial colonization and changes in aggregate stability. Plant
and Soil, 23: 17–33.
Grossman, R.B. and Reinsch, T.G.(2002): Bulk Density andpp.199–224. ASA and SSSA, Madison, WI, USA.
Minh, V.Q. and Tri, L.Q. (2006): Soils of the Mekong Delta, basedon WRB (World Reference Based) — FAO system, at the scale

論文：Effects of soil amendments on pH and aggregate stability of saline sodic soil and acid sulfate soil
1/250.000. Scientific Research, pp.147–156. Faculty of Agriculture and Applied Biology, Can Tho University.

17

istry (4th edition). John Wiley & Sons, Ltd., West Sussex, UK.
Sumner, M.E. and Miller, W.P. (1996): Cation exchange capacity

Naramabuye, F.X. and Haynes, R.J. (2006a): Effect of organicand exchange coefficients. In: Sparks D.L. et al. (Ed.) Meth-amendments on soil pH and Al solubility and use of laboratory

ods of soil analysis. Part 3 — Chemical methods. SSSA Book

indices to predict their liming effect. Soil Science, 171(10):Series No.5, pp. 1201–1230. SSSA and ASA, Madison, WI,

754–763.

USA.

Naramabuye, F.X. and Haynes, R.J. (2006b): Short-term effects

Tho, H.T. and Egashira, K. (1976): Some chemical, physical andon three animal manures on soil pH and Al solubility. Aust. J.

mineralogical properties of acid sulfate soils from the Mekong

Soil Res., 44: 515–521.
Nelson, P.N. and Oades, J.M. (1998): Organic matter, sodicity andsoil structure. In Sumner, M. E. and Maidu, R. I. (Ed.) Sodic

Delta in Vietnam. J. Fac. Agr., Kyushu Univ., 20: 151–164.
Tisdall, J.M. and Oades, J.M. (1982): Organic matter and waterstable aggregates in soils. J. of Soil. Sci., 33: 141–163.

soils. Distribution, processes, management and environmental

USSL (United States Salinity Laboratory) Staff (1954): Diagno-

consequences, pp. 51–75. Oxford University Press, New York,sis and improvement of saline and alkali soils, Agricultural

USA.
Pietri, J.C.A. and Brookes, P.C. (2008): Relationships between
soil pH and microbial properties in a UK arable soil. Soil Biol.
and Biochem., 40: 1856–1861.
Quirk, J.P. and Murray, R.S. (1991): Towards a model for soil
structural behavior. Aust. J. Soil Res., 29: 829–867.

Handbook No. 60, US Department of Agriculture.
Vermang, J., Demeyer, V., Cornelis, W.M. and Gabriels, D.
(2009): Aggregate stability and erosion response to antecedentwater content of a loess soil. Soil Sci. Soc. Am. J., 73(3): 718–
726.
Viet Nam – Netherlands Cooperation (2011):

Towards a

Rhoades, J.D. (1996): Electrical conductivity and total dissolved

Mekong Delta plan. Synthesis of water sector assess-solids. In Sparks D.L. et al. (Ed.) Methods of Soil Analysis.

ment. Programme partners for water, The Netherlands.

Part 3. Chemical Methods. SSSA Book Series No 5, pp. 417–

http://edepot.wur.nl/330185 (Visit date in this page: 2018 Au-

435. SSSA and ASA, Madison, WI, USA.

gust 28.)

Roth, C.H. and Pavan, M.A. (1991): Effects of lime and gypsum

Whalen, J.K., Chang, C. and Clayton, G.W. (2002): Cattle manure

on clay dispersion and infiltration in samples of a Brazilian

and lime amendments to improve crop production of acidic

Oxisol. Geoderma, 48: 351–361.

soils in northern Alberta. Can. J. Soil Sci., 82: 227–238.

Shainberg, I. and Letey, J. (1984): Response of soils to sodic andsaline conditions. Hilgardia, 52: 1–57.
Sims, J.T. (1996): Lime requirement. In Sparks D.L. et al. (Ed.)

Wortmann, C.S. and Shapiro, A.C.A. (2008): The effects of manure application on soil aggregation. Nutr. Cycl. Agroecosyst.,
80: 173–180.

Methods of soil analysis. Part 3 — Chemical methods, SSSA

Xue, D., Huang, X., Yao, H. and Huang, C. (2010): Effect ofBook Series No 5, pp. 491–515. SSSA and ASA, Madison,lime application on microbial community in acidic tea orchard

WI, USA.

soils in comparison with those in wasteland and forest soils. J.

Skjemstad, J.O. and J.A. Baldock (2006): Chapter 21. Total andEnviron. Sci., 22(8): 1253 –1260.

organic carbon. In Carter, M.R and Gregorich, E.G. (Ed.) Soil

Yan, F., Schubert, S. and Mengel, K. (1996): Soil pH increasesampling and method of analysis. 2nd edition, pp. 225–236.

due to biological decarboxylation of organic anions. Soil. Biol.

CRC Press, FL, USA.

Biochem., 28(4/5): 617–624.

Stefansson, A. (2007): Iron (III) hydrolysis and solubility at 25◦ C.
Environ. Sci. Technol., 41(17): 6117–6123.
Strawn, D.G., Bohn, H.L. and O’Connor, G.A. (2015): Soil chem-

Yoder, R.E. (1936): A direct method of aggregate analysis of soils
and a study of the physical nature of erosion losses. J. of Am.
Soc. of Agronomy, 28: 337–351.

18

土壌の物理性

第 141 号要(2019)

旨

メコンデルタには硫酸酸性土壌や塩類土壌が広く分布する．土壌の化学性の改良の際には，物理性の劣化を最小限にすることも重要である．また，メコンデルタの土壌団粒については，よくわかっていない．
そこで本研究では, 塩性 Na 土（SS，pH= 5.5），硫酸酸性土 (ASS，pH= 2.7) と沖積土（AS，pH= 4.6)に卵殻（CaCO3 の代替）ならびに鶏ふん堆肥（以下鶏ふん）を施用した後，土壌 pH と団粒安定性の変化を調べた．培養は，土壌と鶏ふん，卵殻を混合した後，室温 25 ◦ C の下，圃場容水量で適宜換気，CO2
測定をしながら 45 日間実施した．団粒安定性評価は予め行った団粒安定性試験を参考に培養後の土壌から 2 ∼ 5 mm サイズの風乾試料を調製し，これを急速に漬水した後の平均重量直径で行った．CO2 発
生量から，鶏ふん施用 SS，AS では，鶏ふんの分解が示唆されたが，ASS ではほとんど分解しなかった．鶏ふん · 卵殻混合物施用の場合，ASS では，初期に卵殻の炭酸 Ca の反応，その後は鶏ふん等有機物の分解が，SS と AS ではいずれも鶏ふん等有機物の分解が CO2 発生の主因であると考えられた．鶏ふんは，施用量に応じて SS と AS の pH を改善したが ASS では pH 改善効果がなかった．鶏ふん · 卵殻混合物を施用すると ASS において卵殻のみの場合よりも有意に pH が上昇し，有機物の分解も pH 改善に寄与していることが示唆された．鶏ふんならびに鶏ふん · 卵殻混合物の施用後，団粒安定性が向上した．特に pH が非常に低い ASS において，卵殻の炭酸 Ca による pH 上昇が鶏ふん等有機物分解による，団粒安定性向上促進に寄与したと考えられる．
キーワード：土壌改良，土壌構造，鶏ふん堆肥，卵殻，土壌劣化