IJERD – International Journal of Environmental and Rural Development (2011) 2–1

Research article
erd

Ecological Management in Salt-affected Area of NortheastThailand: Monitoring Soil Quality
AUNG NAING OO
Faculty of Agriculture, Khon Kaen University, Khon Kaen, Thailand
Email:ano1972@gmail.com;chulee_b@kku.ac.th

CHULEEMAS BOONTHAI IWAI
Faculty of Agriculture, Khon Kaen University, Khon Kaen, Thailand

BUBPHA TOPARK-NGARM
Faculty of Agriculture, Khon Kaen University, Khon Kaen, Thailand
Received 10 December 2010

Accepted 20 January 2011

Abstract Soil salinity has become one of the major determinants of crop productivity inNortheast Thailand, and has an adverse impact on the physical, chemical and biologicalproperties of soil, as well as plant growth and yield. Ecological management of soil isessential to sustainable production. Soil microorganism may fulfill many important
ecological roles including decomposition and nutrient cycling in salt-affected area. This
study aimed to monitor the impact of salinity on soil properties under tree plantation at
Amphur Borabue, Mahasarakam Province, Northeast Thailand. The study area wasdivided into 3 zones followed by the plant community found in each area which correlatedwith the flooding situation and soil salinity. Soil samples were collected from threedifferent zones at the same depth (0-20cm) with three replications during the rainy seasonsof 2008 and 2010 in order to analyze soil physical, chemical and biological properties. Theresults showed that biodiversity of soil biota and soil microbial activity in terms of soil
microbial carbon, soil microbial nitrogen and soil respiration after tree plantation was
higher than before. The EC, Na and K values were decreased, whereas pH, OM and N
were increased after tree plantation. It could be concluded that soil physical, chemical andbiological properties were improved after tree plantation. Therefore, this result would bevaluable for sustainable land resources improvement and rehabilitation.
Keywords salinity, ecological management, soil quality

INTRODUCTION
Awareness of the ecological and environmental health of ecosystems around the world has been
increasing in recent years. As a result, there has been a growing interest in sustainable agricultural
alternative practices. In Thailand, the agricultural society has been criticized for problems with soil
salinity, soil degradation, greenhouse gas release into the atmosphere, water pollution and a loss ofwildlife habitat. Tree plantation has been associated with an increasing quantity of environmental
and ecological benefits such as enhancement of microclimatic conditions, improved utilizing andcycling of soil nutrients, improved soil and water quality, creation of suitable habitats for insect andanimal species, protection from erosion, and protection from wind (Jose et al., 2004). Ecologicalmanagement such as tree plantation in salt-affected areas has the potential to alleviate salinity stresson farms for sustainable production.
Soils in Northeast Thailand are salt-affected due to salt bearing rocks (Department of Land
Development, 1991), particularly in Nakhon Ratchasima, Khon Kean, Roi Et and Mahasarakham
provinces (Department of Mineral Resources, 1982). Soil salinity has become one of the major
determinants of crop productivity in those areas, and might have an adverse impact on soil physicalproperties (Boivin et al., 2004), chemical properties (Sumner, 2000) and soil microbial© ISERD43

IJERD – International Journal of Environmental and Rural Development (2011) 2–1

communities and activities (Zahran, 1997; Sardinha et al., 2003) and also influence on plant growthand yield (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).
Salt-affected soils may be reclaimed by growing salt-tolerant tree species, which improve thephysical and chemical properties as well as biological activity in the soil (Garg, 1998).
Investigations carried out at various research locations in India have shown that salt-affected soilcan be improved by trees plantation. For example, incorporation of trees in the land can help inmaintaining the nutrient pool and enhance soil fertility (Young, 1997; Rao et al., 1998). Tejwani(1994) also reported that tree plantation is an excellent strategy for reclamation of salt-affectedsoils. Tree litter improves soil fertility not only through the release of nutrients in the soil bymineralization but by also adding soil organic matter. Thevathasan and Gordon (2004) also
reported that tree intercropping under temperate significantly enhanced the diversity of birds,insects, and earthworms; increased soil organic carbon content and N cycling; and improved soilquality. The objective of this study was to monitor the impact of salinity on soil quality under tree
plantation in salt-affected area of Northeast Thailand.
MATERIALS AND METHODS
Study area
This study was carried out at Ak-Kasatsuntorn water reservoir, Tumbon 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 area was divided into 3 zones followed by the plant community
found in each area where they are correlated with the flooding situation and soil salinity. The studysite has been established for three years with tree plantation (2710 plants of 17 species). Woody
plants such as common ironwood (Casuarina equisetifalia J.R. & C. Forst) and fruit plants such asmanila tamarind (Pithecolobium dulce) in salt-affected area were grown covering with native
grasses and weeds, i.e., torpedograss (Panicum repens L.).
Soil sampling and analysis
Soil was sampled from three random locations of each zone and unplanted soil near experimentalsite (control) at the depth of 0–20 cm during the rainy seasons of 2008 and 2010. The soils wereanalyzed to determine soil physical and chemical properties according to routine methods of theLand Resources and Environment section, Faculty of Agriculture, Khon Kaen University. Soil
texture was determined by hydrometer method. Soil pH and electrical conductivity (EC) weredetermined in a 1:2.5 and 1:5 soil to water solution by pH meter and EC meter, respectively. Cationexchange capacity (CEC) was determined by 1 N ammonium acetate method. Total nitrogen (N)was measured by Kjeldahl method; available phosphorus (P) by the Olsen method, exchangeable
potassium (K) by 1 N ammonium acetate and flame photometry; and total organic matter (OM) byusing Walkley and Black method.
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. Besides, non-fumigated samples were extracted
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 and employing 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 soil respiration using titrimetric method (Zuberer, 1991). Thismethod was based on the determination of CO2 evolved from the soils. Field moist soil (200g) was
placed and incubated at 28°C in an airtight jar containing a vial with 15 ml of 1.0 M NaOH. After© ISERD

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IJERD – International Journal of Environmental and Rural Development (2011) 2–1

incubation of a day, the NaOH solution was removed and the trapped CO2 titrated with 0.5 M HClafter precipitating the carbonate with excess 0.5 M BaCl2. Soil respiration, i.e., evolved CO2-C, wascomputed according to the equation (1) described by Anderson (1982) as shown below:
CO2-C (mg) = (B-V) NE(1)where B is the volume (ml) of acid (HCl) used to titrate the alkali (NaOH) of blank (no soil), V isthe volume (ml) of acid used to titrate the soil sample, N is the normality of acid (HCl), and E isequivalent weight of CO2-C. The metabolic quotient qCO2 (Anderson and Domsch, 1986) of eachsampling period was calculated by using equation (2).
qCO2 = CO2-C / MBC(2)-1-1

where CO2-C (mg kg soil) is soil respiration and MBC (mg kg soil) is microbial biomass C.
Statistical analysis: The data recorded was analyzed statistically using Statistix 8.0 softwareand Microsoft Excel software (2007) to compare each zone at 5% probability level.
RESULTS AND DISCUSSION
Soil physical and chemical properties
In this study, tree plantation covered with native grasses had a significant impact on soil physicalproperties of salt-affected soil. Soil texture of study area was sandy soil. Bulk density decreased
from 1.72 g cm-1 to 1.55 g cm-1 under tree plantation, whereas soil moisture content increased from
9.3% to 13.5%.
Several soil chemical properties of salt-affected area were influenced by tree plantation andtime (Fig. 1). Three years after planting (in 2010), decreases in the values of EC, Na, and K in thesoil became apparent in growing trees when compared with the first year after planting (in 2008).
Soil organic matter (OM) and total nitrogen (N) content in all zones by tree plantation increased
with time since 2008, which were from 0.53 % and 0.057% in the first year after planting to 0.73%
and 0.086 % in three years after planting, respectively. The increases in CEC, OM and N content
could be attributed to the addition of leaf litter and root decay, which improved microbial activity
in soil. The results confirm the findings of Mishra et al. (2004). Although there were no significant
differences in pH and available P between tree plantation and unplanted soil, there were slightincreases in all zones in year 2010.
Soil biological properties
The MBC and MBN values in 2008 and 2010 were significantly higher in tree plantation than inunplanted soil, with the highest value being with zone 3 (Fig. 2). It might be due to theaccumulation of humus from decomposition of leaf litter and root decay, which increased soilorganic C. Soil respiration, as a good index of the activity of microorganisms, was consistently
lower in the unplanted soil when compared to tree plantation zones in both years 2008 and 2010.
These results are in accordance to other findings, which showed decreased soil respiration(Sardinha et al., 2003; Tripathi et al., 2006) in natural saline soils. The metabolic quotient (qCO2)
was higher in 2008, probably as a result of stress by salinity on soil microflora (Anderson andDomsch, 1993; Rasul et al., 2006), whereas it tended to lower in 2010. A low metabolic quotient
implies that the microbial populations were energetically efficient, i.e., allocating proportionallymore carbon to growth (biosynthesis) than to maintenance (Zak et al., 1994).
There was a significant negative relationship between EC and microbial biomass C, microbial
biomass N, basal soil respiration and metabolic quotient (Fig. 3). This relationship revealed thedetrimental effect that soil salinity had on the soil microbial activity. These results are in line withthe findings of Yuan et al. (2007). Increased soil microbial activity might be due to the ameliorative
effects of trees and consequently organic matter inputs. According to Rao and Pathak (1996),
carbon is an important factor influencing microbial activity in salt-affected soils.
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Biodiversity  index  (H′)  of  soil  biota  in  zone  1,  zone  2  and    zone  3  were  0.11,  0.63  and  0.71  in  the first year after planting and 0.23, 0.95 and 0.75 in three years after planting, respectively. The
results observed that biodiversity of soil biota after tree plantation was higher than before.

Fig. 1 Soil chemical properties of salt-affected soils after tree plantation(2008 is the first year after plantation and 2010 is three years after plantation;
Bars represent standard deviation)

Fig. 2 Soil microbial parameters of salt-affected soils after tree plantation(2008 is the first year after plantation and 2010 is three years after plantation;
Bars represent standard deviation)© ISERD46

IJERD – International Journal of Environmental and Rural Development (2011) 2–1

Fig. 3 Relationship of microbial parameters with electrical conductivity of salt-affected soils(Regression equation, line of best fit and R2 were shown)

CONCLUSION
Monitoring in salt-affected soil grown with tree species indicated more efficient changes in termsof dropping EC and decreasing Na+ levels in the soil. In contrast, evidence of increased organic
matter and total nitrogen showed after tree plantation. Likewise, there was greater microbialactivity in salt-affected soil under tree plantation. It could be concluded that soil physical, chemicaland biological properties were improved after tree plantation covered with native grasses in saltaffected soil. Therefore, it is pertinent that tree plantation has a great scope and potential in termsof ecologically sustainable land resources improvement and rehabilitation.
ACKNOWLEDGEMENT
This  study  was  supported  by  the  Research  Project:  “Problem  Soils  in  Northeast  Thailand”, Khon
Kaen University, Thailand and the KKU Research Project “Improvement of Soil Fertility andBiodiversity in the Salt-Affected Lowland Area by Various Species Trees Pantation”.
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