IJERD – International Journal of Environmental and Rural Development (2012) 3-1

Research article
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Soil Carbon Dynamics during the Amelioration of SaltAffected Areas in Northeast Thailand
AUNG NAING OO
Faculty of Agriculture, Khon Kaen University, Khon Kaen, Thailand
E-mail: ano1972@gmail.com

CHULEEMAS BOONTHAI IWAI*
Faculty of Agriculture, Khon Kaen University, Khon Kaen, Thailand
E-mail: chulee_b@kku.ac.th

PATCHAREE SAENJAN
Faculty of Agriculture, Khon Kaen University, Khon Kaen, Thailand

BUBPHA TOPARK-NGARM
Faculty of Agriculture, Khon Kaen University, Khon Kaen, Thailand
Received: 15 December 2011

Accepted 2 April 2012(*: Corresponding Author)

Abstract An understanding of the effect of salinization on soil carbon (C) sequestration isimportant for environmental management. This study aimed to investigate the effect ofsalinity on soil organic carbon dynamics in salt-affected areas under a tree plantation, at
Amphur Borabue, Mahasarakam province, Northeast Thailand. The study area has been
established with tree plantation for three years and was divided into 3 zones based on theplant community found in each zone, correlated with the flooding situation and soil
salinity. Soil samples were taken from three different zones and a fallow soil (control) at
the same depth (0-20 cm) with three replications beginning from the rainy season of 2010
to the summer of 2011. The results from a three year old tree plantation showed decreasing
ECe and increasing soil organic carbon when compared with the fallow soil. Moreover,microbial activities were greater under the tree plantation soils when compared to thefallow soil. It could be concluded that soil organic carbon and biological properties were
improved after establishment of a tree plantation in salt-affected soils. Therefore, it
indicates that tree plantations are an effective strategy for carbon sequestration to reducethe buildup of carbon dioxide in the atmosphere.
Keywords salinity, carbon sequestration, microbial activity

INTRODUCTION
An understanding of the effect of salinization on soil carbon (C) sequestration is important forenvironmental management. Soils in Northeast Thailand are salt-affected due to the presence of salt
bearing rocks (Land Development Department, 1991), particularly in Nakhon Ratchasima, Khon
Kaen, Roi Et and Mahasarakham provinces (Department of Mineral Resources, 1982). Because of
their age and the extent of weathering that has taken place in the past, soils in those areas are also
relatively infertile. Levels of soil fertility are often strongly influenced by soil organic carbon(SOC), with low organic matter contents due to low biomass inputs and rapid turnover.
Since the amount of C present in the soil is dependent on C inputs and losses, increasing
salinity levels have the potential to decrease C inputs into the soil through their effects onvegetation and impact on C dynamics. Not only high salinity directly impacts upon plant vigour
through changes in osmotic potential, ion toxicities and ion deficiencies, but indirect effects onvegetation can result from altered soil conditions such as increased dispersion and decreased
permeability. Changes in salinity affect soil physical (Boivin et al., 2004) and chemical properties(Sumner, 2000), which subsequently alter nutrient cycles, aggregation and biotic activityⒸ ISERD

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IJERD – International Journal of Environmental and Rural Development (2012) 3-1(Zahran,97; Sardinha et al., 2003; Rietz and Haynes, 2003) and also influence on plant growth andyield (Marschner, 1995). Among them, changes in mineralization of C and N with increasing
salinity have been observed (Nelson et al., 1996; Pathak and Rao, 1998). Despite the large area
affected by salinity, both in Thailand and globally, data on the changes in soil C stocks in thesedegraded environments is scarce.
Carbon sequestration refers to the storage of atmospheric CO2 in the plant biomass and soils ofa particular ecosystem during a period of time. Tree-based plantation is a land management optionthat has C sequestration potential for two reasons. First, tree biomass contains more C than annual
crops, leading to more C storage in tree plantation systems than conventional agricultural systems(Sharrow and Ismail, 2004; Peichl et al., 2006). Second, tree plantation systems are expected tohave more SOC due to the greater annual C input from leaf litter, tree root turnover and tree root
exudates, compared to agricultural crops. Organic residues from trees are lignin-rich and containother resistant compounds (e.g., tannins) that are slowly decomposed and thus stabilized in the
SOC pool (Montagnini and Nair, 2004). Garg (1998) also reported that salt-affected soils may bereclaimed by growing salt-tolerant tree species, which improve the physical and chemical
properties as well as biological activity in the soil. Therefore, ecological management utilizing tree
plantations in salt-affected areas has the potential to alleviate salinity stress and increase soilorganic carbon. The objective of this study was to investigate the effect of salinity on soil organiccarbon dynamics under tree plantations in salt-affected areas of Northeast Thailand.
MATERIALS AND METHODS
Study area
This study was carried out at Ak-Kasatsuntorn water reservoir, Tambon Borabue, Mahasarakam
Province, Thailand at latitude of 16° 01' N and longitude of 103° 05' E, and at an elevation of 178
m from mean sea level. The study site has been established for three years with a tree plantation(2710 plants of 17 species). Woody plants such as common ironwood ( Casuarina equisetifalia J.R.
& C. Forst.) and fruit plants such as manila tamarind (Pithecolobium dulce) are growing in a saltaffected area with a covering of native grasses and weeds, i.e., torpedograss (Panicum repens L.).
The study area was divided into 3 zones based on the plant type located in each area where they
were correlated with the flooding situation and soil salinity. Zone 1 is more prone to flooding
situation and high salinity, followed by Zone 2 and Zone 3.
Soil sampling and analysis
Soil samples were taken from three randomly selected locations at each zone and from a fallow soil
near the experimental site (control) at a depth of 0–20 cm beginning from the rainy season of 2010
to the summer of 2011. Samples were analyzed to determine soil chemical and microbial properties
in the laboratory at the Land Resources and Environment section, Faculty of Agriculture, Khon
Kaen University. Electrical conductivity in saturated paste extracts (ECe) was measured following
the method described by the United States Department of Agriculture (USDA, 1954). Total soilorganic carbon (SOC) was determined by the method of Walkley and Black.
Microbial biomass C and N were determined in field moist subsamples immediately after
sampling by the chloroform fumigation extraction method. For microbial biomass C (MBC), 20 gof fumigated and unfumigated soil were extracted with 100 ml of 0.5 M K 2SO4. MBC in theextracts was determined after oxidation with K2Cr2O7. For microbial biomass N (MBN), 20 g ofsoil was extracted with 100 ml of 1 M KCl. Extracts were taken from non-fumigated samples
immediately after sampling. MBN was determined by the ninhydrin-reactive N method (Amato andLadd, 1988). MBC and MBN were calculated as the difference between fumigated andunfumigated values, using kEC and kEN factors of 0.33 (Sparling and West, 1988) and 3.1 (Amato
and Ladd, 1988) to convert extracted organic C and N to microbial C and N, respectively.
Microbial activity was studied by basal soil respiration using the titrimetric method (Zuberer, 1991).
This method was based on the determination of CO2 evolved from incubated soils. Field moist soil
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was placed in an airtight jar containing a vial with 15 ml of 1.0 M NaOH and incubated at 28°C.
After one day of incubation, the NaOH vital was removed from the jar, 5 ml of excess 0.5 M BaCl 2
and 2-3 drops of phenolphthalein added to precipitate carbonate out from the NaOH solution as
insoluble barium carbonate, and finally the excess NaOH was titrated with 0.5 M HCl. Soil
respiration, i.e., evolved CO2-C, was computed according to the Eq. (1) described by Anderson(1982).
CO2-C (mg) = (B-V) NE(1)

where B is the volume (ml) of acid (HCl) used to titrate the alkali (NaOH) of a blank solution(not incubated with soil), V is the volume (ml) of acid used to titrate the alkali solution incubatedwith the soil sample, N is the normality of acid (HCl), and E is the equivalent weight of CO 2-C.
The metabolic quotient qCO2 (Anderson and Domsch, 1986) of each sampling period was
calculated as in Eq. (2).
qCO2 = CO2-C / MBC(2)

where CO2-C (mg kg-1 soil) is soil respiration and MBC (mg kg-1 soil) is microbial biomass C.
Statistical analysis: The data analysis was done using Statistix 8.0 (Analytical Software, 2003)
to compare each zone at 5% probability level by using least significant different (LSD) method.
RESULTS AND DISCUSSION
The results from a three year old tree plantation with cover of native grasses showed significant
effects on soil properties of this salt-affected soil. Soil texture of study area was sandy soil. There
were significant differences in ECe among the zones in all seasons (Table 1). The fallow soil(control) and zone 1 were saline soils (greater than 4 dS m-1) while the others were non-saline (lessthan 4 dS m-1), according to the classification of the USDA (1954). In the rainy season, the average
ECe was 9.02 dS m-1 and then decreased during the winter season (6.06 dS m-1) and peaked in thesummer season (12.22 dS m-1), presumably due to salts in the groundwater moving up in the soil
profile, accumulating on the soil surface, and consequently increasing the salinity in the summer
season (Topark-Ngarm et al., 1990).
Table 1 Electrical conductivity (ECe) and total soil organic carbon (SOC) in salt-affected soils
after three years plantation

Control
Zone 1
Zone 2
Zone 3Mean
F-testCV (%)

Rainy
17.83 a15.54 a1.25 b
1.45 b9.02*
17

ECe (dS m-1)
Winter
14.20 a9.41 b0.34 c0.28 c6.06**
27

Summer
26.87 a17.39 b2.83 c1.80 c
12.22
**
14

Rainy
1.80 b
3.51 ab4.90 a4.97 a3.79*
24

SOC (g kg-1)
Winter2.80 c4.04 b
5.30 a5.50 a4.41**
9Summer
1.71 c2.10 c4.21 b
5.27 a3.32**
7

Values in the same column followed by the same letter are not significantly different at the 5% level by the LSD test,**    significantly  different  at  P≤0.01,  *    significantly  different  at  P≤0.05

Total soil organic carbon was significantly higher in the tree plantation zones than in thefallow soil (control) in all seasons, with the highest value being in zone 3 (Table 1). It might be dueto the accumulation of humus from decomposition of leaf litter and root decay, which increased
soil organic C. The results confirm the findings of Mishra et al. (2004). SOC contents of all zones
were higher in the winter season, whereas values for the rainy and summer seasons were lower. It
could be explained that the leftover leaf and root masses might have contributed to the increase OC
content during the winter season.
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The activity of MBC was greatly influenced by salinity (Table 2). It was significantly higher
in the zone 2 and 3 when compared to the control in all seasons. It was not different between thezone 1 and control in the summer season, indicating that the zone 1 was still affected by salinity. In
the rainy and winter seasons, there was significant difference between the zone 1 and control,
probably due to high soil organic carbon in the zone 1 (Table 1). Among seasons, the highest
average MBC was recorded in the rainy season. In contrast, the lowest was in summer whensalinity was the highest, probably due to capillary rise of salty groundwater associated with
evaporation (Topark-Ngarm et al., 1990). Soil salinity can decrease the microbial activity during
summer season (Rietz and Haynes, 2003), and it is probably one of the environmental stresses for
microbial growth and proliferation in soil. In this study, the values of MBC were higher in soils
with higher SOC contents, as a similar result of Sparling, 1997. The values of MBN showed asimilar pattern to those of MBC (Table 2). It was lowest in soil with highest ECe.
Table 2 Soil microbial biomass carbon (C) and nitrogen (N) in salt-affected soils after three
years plantation
LocationControl
Zone 1
Zone 2
Zone 3Mean
F-testCV (%)

Microbial biomass C (mg kg-1)
Rainy
WinterSummer
99.4 c60.1 c43.8 c164.4 b135.7 b45.3 c176.0 b175.9 ab151.5 b228.5 a202.1 a183.9 a
168.2
143.5
106.1
*
**
**
18
22
11

Microbial biomass N (mg kg-1)
Rainy
WinterSummer
15.6 b8.1 c
7.3 c
17.6 b
11.4 c9.0 c28.6 a22.6 b
18.4 b
35.9 a28.5 a23.9 a
24.4
17.6
14.7
**
**
**
21
13
11

Values in the same column followed by the same letter are not significantly different at the 5% level by the LSD test,**    significantly  different  at  P≤0.01,  *    significantly  different  at  P≤0.05

Soil respiration, as a good index of the activity of microorganisms, was consistently lower inthe control when compared to the tree plantation zones in all seasons (Table 3). It was highest in
the zone 3 with highest SOC content that supports more CO2 respiration. Variability in soil
respiration mainly depends on weather variables (Kucera and Kirkham, 1971) and soil moisture(Gupta and Singh, 1981), along with the salt content of salt-affected soils (Garcia and Hernandez,
1996).
Table 3 Soil microbial basal respiration and metabolic quotient in salt-affected soils after
three years plantation
LocationControl
Zone 1
Zone 2
Zone 3Mean
F-testCV (%)

Soil microbial basal respiration(mg CO2-C kg-1 day-1)
Rainy
WinterSummer
18.7 b9.5 b
4.1 b
22.6 a10.6 a5.0 b22.7 a12.7 a10.1 a23.1 a17.6 a11.6 a
21.8
12.6
7.7
*
*
**
6
19
11

Metabolic quotient (qCO2)(μg  CO2-C mg-1 MBC h-1)
Rainy
WinterSummer
8.0 a
7.1 a
3.9 c
5.8 b
3.3 b
3.1 c
5.5 b
3.0 b
2.8 b
4.2 b
3.6 b
2.6 a
5.9
4.3
3.1
*
*
*
16
28
14

Values in the same column followed by the same letter are not significantly different at the 5% level by the LSD test,**    significantly  different  at  P≤0.01,  *    significantly  different  at  P≤0.05

The metabolic quotient (qCO2) was higher in the control when compared to the tree plantation
zones in all seasons. It was probably as a result of stress by salinity on soil microflora (Anderson
and Domsch, 1993; Rasul et al., 2006), whereas it tended to lower in the tree plantation zones. A
low metabolic quotient implies that the microbial populations were energetically efficient, i.e.,
allocating proportionally more carbon to growth (biosynthesis) than to maintenance (Zak et al.,Ⓒ ISERD

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1994). It was highest in the most saline soils, which may indicate low substrate quality (Smith,1993) and low efficiency of organism functioning (Anderson and Domsch, 1990).
There were negative correlations between ECe and SOC (r= -0.90, P≤0.01,   n=36),   between
ECe and MBC (r= -0.78, P≤0.01,  n=36),  between ECe and MBN (r= -0.77, P≤0.01,  n=36),  between
ECe and soil respiration (r= -0.42, P≤0.01,   n=36). These relationships revealed the detrimental
effects that soil salinity had on the soil microbial activity. There was also a positive correlation
between MBC and SOC (r= 0.83, P≤0.01,  n=36), possibly because MBC is a part of SOC (Sparling,1997). According to Rao and Pathak (1996), carbon is an important factor influencing microbialactivity in salt-affected soils. Therefore, increased soil microbial activity might be due to theameliorative effects of trees and consequently organic matter inputs.
CONCLUSION
The amelioration of salt-affected soil grown with tree species showed decreasing of ECe andincreasing of soil organic carbon. In addition, there were greater microbial activities in salt-affectedsoil under tree plantations. It could be concluded that soil chemical and biological properties were
improved after establishment of a tree plantation in salt-affected soil. Therefore, it indicates thattree plantations are one of the most effective strategies for carbon sequestration to reduce thebuildup of carbon dioxide in the atmosphere.
ACKNOWLEDGEMENTS
This study   was   supported   by   the   research   project:   “Problem   Soils   in   Northeast   Thailand”,   Khon  Kaen University, Thailand and   the   research   project   “Using   Soil   Biota   for   Biological   Monitoring  and Ecological Zoning in the Salt-Affected   Area  in  Northeast  Thailand”. Also, we would like toexpress our gratitude to the Highyer Education Research Promotion and National Research
University Project of Thailand, Office of the Higher Education Commission, WNEC and GWRC,
Khon Kaen University, Thailand.
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