IJERD – International Journal of Environmental and Rural Development (2013) 4-1

Research article
erd

Factors Affecting Rice Production in Northeastern
Thailand: The Relationship between Soil Salinity andVegetative Cover
CHARUWAN PHAITHONG
Khon Kaen University, Khon Kaen, Thailand
Email: serf_444@hotmail.com

ADCHARAPORN PAGDEE*
Khon Kaen University, Khon Kaen, Thailand
Email: adcpag@kku.ac.th
Received 16 December 2012

Accepted 30 January 2013(*Corresponding Author)

Abstract Saline soil is typically found in lower elevation terrain which is also used for ricecultivation. Deforestation in recharge areas can accelerate soil salinity due to increased
capillary action. This study examined the relationship between saline soil distribution andvegetative cover at Nong Due Village, Khon Kaen, Thailand. It also identified some social
factors and farm management practices which affected rice production in saline paddies.
A field survey was conducted in April, 2012 to determine soil property analysis, combinedwith   a   questionnaire   on   rice   production,   farm   management,   and   farmer’s   household  socioeconomic conditions. In total, 34 paddy fields were surveyed with 68 soil samples
collected from non-saline and saline plots. Elevations of the sampled plots were 146-178
m with electrical conductivity (ECe) 0.19-16.58 dS/m. Soil salinity did not show asignificant correlation from the sampled paddies to the closest vegetation, but high salinity
did occur in lower elevations and farther away from the nearest forest. Forty household
representatives answered the questionnaire, of which 34 had encountered some problems
with soil salinity (average 0.89 ha/household). Average rice yields from saline paddies
were 1.9 tons/ha, lower than those from non-saline paddies (mean difference -113.39
kg/ha). Rice production costs associated with soil salinity were estimated 10,770 Baht/ha,of which the highest amount was spent on crop maintenance. In contrast, costs from nonsaline farming systems were 9,791 Baht/ha (39.75% also spent on farm maintenance).
Household income and labor did not show a significant correlation with farm management
practices. Fertilizer application is dependent on the availability of on-farm resources andword-of-mouth. Farmers often use cattle manure, compost and green manure to reduce soil
salinity. Moreover, farmers raised the height of paddy borders, so that more rainwater
could be stored, thus ensuring that the rice paddies were continuously submerged.
Keywords soil salinity, saline paddies, vegetative cover, rice production,
Nong Due village

INTRODUCTION
Soil salinity is a major problem in semi-arid or arid regions around the world. For example, Arunin(1996) reported 17.81 million ha of salt-affected areas in northeastern Thailand (approximately
17% of the region). According to Yuvaniyama (2003), two important factors that cause saline soil
distribution are: 1) the presence of salt rock in Maha Sarakham geological formation which induces
salt-dissolved water to the topsoil through capillary action; and 2) land use activities, such as
deforestation in recharge areas, that accelerate dissolved salt transfer to the surface (Land
Development Department, 2009). Soil salinity reaches a steady state when the amount of salt
intruding into the soil profile is equaled by the amount leaving the soil surface via stream flow.
This phenomenon is widespread in rice paddy fields where salt accumulates easily and graduallyⒸ ISERD

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IJERD – International Journal of Environmental and Rural Development (2013) 4-1

deteriorates over time (Barrett-Lennard, 2002). Sayok et al. (1993) reported that soil EC measures
for specific clear-cut areas in the Davy Crockett National Forest near Apple Springs, Texas werehigher than adjacent, undisturbed forest land.
Economically speaking, rice (Oryza sativa L.)  is  Thailand’s  most  important  cash  crop.  During
2009-2011, Thailand exported about 9.42 million tons of rice annually, estimated at USD 5.18
million per year (Office of Agriculture Economics of Thailand, 2012). In 2011, the total harvested
paddies were estimated at 8.91 million ha, of which about 5.55 million ha (62.22%) were from theNortheast  (12.01  million  tons  accounted  for  51.60%  of  Thailand’s  total  rice  production). Althoughthe  region’s  total  rice  production  is  relatively  high,  the  yield  per  unit  area  is  only  2.02  tons/ha  as  compared to the national average yield of 2.38 tons/ha (Office of Agriculture Economics ofThailand, 2012). This is due to several factors,  including  the  region’s  climatic  conditions,  poor  soil  fertility, low inputs (Wijnhoud et al., 2003) and soil salinity (Quantin et al., 2008). Rice yields andeconomic returns are about one third less in saline soil as compared with nearby unaffected areas(Hall et al., 2004).
Salinity has a harmful impact on soils and crop production. Excessive amounts of salt
adversely affect the physical and chemical properties of soil, as well as microbiological processes(Lakhdar et al., 2009). Salinity and sodicity also affect crop yields because of osmotic effects andsodium toxicity (Marschner, 1995). If nutrient up-take efficiency decreases, then plants will suffer.
For example, nitrogen deficiency expresses itself in older leaves of rice – those having a pale anddry leaf apex. Prolonged nitrogen deficiency causes severe plant stunting, reduced tillering, andyield reduction. Additionally, increased levels of salt can result in soil compaction, thus reducing
water infiltration and causing difficulty in plowing. Wijnhoud et al. (2003) stated that farming
decisions often favor rice paddies with higher income potential, thus shifting management priorities
to socioeconomic factors. Family income can also affect farm management practices, including
fertilizer application.
OBJECTIVE
Soil salinity tends to increase when vegetative cover decreases. This can exacerbate land limitation
problems, especially on rice production which takes place in areas where soil salinity typicallyoccurs. Subsequently, ecological factors, such as the availability of nutrients (N-P-K) can affectrice production. Furthermore, farm management practices (e.g., fertilizer application, manure input
and irrigation) play key roles in productivity, but success is heavily dependent upon the farmer’s  socio-economic condition. This study examined several factors affecting rice production at Nong
Due Village, Nong Song Hong district, Khon Kaen province, including the relationship between
saline soil distribution and vegetative cover. Better understanding of soil salinity and riceproduction problems will help farmers to more effectively adapt, thus to a certain extent help
improve their productivity and benefits gained.
METHODOLOGY
Two data collection activities were done. Firstly, soil samples from both saline and non-saline ricepaddies were collected in April, 2012 using a composite sampling method for soil property
analysis, including ECe, organic matter (titration method, modified from Walkley and Black,1934), N (calculation derived from OM values), P (Bray no. II method), K (Flam photometry
method), soil pH, texture and color. Sampled paddy coordinates and elevations were recorded on a
GPS receiver (Garmin etrex). The distance between each sampled plot to the closest forest wasestimated using a Google Earth map. Correlations between soil sample ECe values and distances tothe closest forest, as well as elevations, were calculated to determine the extent of salinity
distribution.
Secondly, a questionnaire was administered to villagers in July, 2012 to measure riceproduction, farm management practices, and household socioeconomic factors. Most of thequantitative data such as rice yields, nutrient inputs, and residue management were provided byⒸ ISERD

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IJERD – International Journal of Environmental and Rural Development (2013) 4-1

farmers during oral interviews. Units were standardized, which involved conversion of volumes toweights. This conversion was checked through direct observations of rice containers and/or sacks.
Descriptive statistics, t-tests and correlations were performed to examine potential factors affecting
rice production.
RESULTS AND DISCUSSION
Nong Due (UTM 48P 263316mE 1733847mN) is a village in Dong Keng sub-district, Nong Song
Hong district, Khon Kaen province, Thailand. Patches of soil salinity can be observed in ricepaddies, especially during the dry season. Rice paddies were primarily located northeast of thevillage adjacent to a dry Dipterocarp forest called Kok Nongjan (KNJ) community forest (UTM
48P 265044mE 1735511mN). The southern side of the village was surrounded by a forest patchwith trees scattered throughout the rice paddies (Fig.1).

B

Fig. 1 Nong Due Village (A): rice paddies and surrounding forests - KNJ (B)(Source: Google Earth, 2012)

Soil salinity distribution
A total of 68 soil samples from both saline and non-saline rice paddies were collected. The sampled
point elevations ranged from 146 m to 178 m with the lowest estimated soil ECe 0.19 dS/m up to
16.58 dS/m. The average distance from non-saline rice paddies to the closest vegetation was 0.28 ±0.10 km, while high salinity sampled plots were found farther away from the forests (Table 1).
Although soil salinity distribution did not show significant correlations with distance, high salinity
areas tended to occur in lower elevations and farther away from vegetative cover.
Table 1 Salinity distribution: sampled point elevation, distance to the closest forest and ECe
ECe (dS/m)
Criterion
Range*
Non saline<20.19- 1.99
Slightly saline soil
2-4
2.33- 3.83
Moderately saline soil
4-8
4.09- 7.49
Highly saline soil
8-16
8.49-14.63
Severely saline soil
>16
16.58
Source: *U.S. Salinity Laboratory Staff (1954)
Salinity level

Elevation (m)Distance (km) to theclosest vegetation

No. of sampled
points (%)

161.95 ± 7.60
159.89 ± 5.37
162.43 ± 4.65
159.20 ± 5.81
161

0.28 ± 0.10
0.29 ± 0.09
0.30 ± 0.11
0.32 ± 0.12
0.30

41 (60.29)
9 (13.24)
7 (10.29)
10 (14.71)
1 (1.47)

Soil properties
Soil samples consisted of loamy sand with high variability of pH (3.64-9.93, median=7.28).
Takuhito et al. (2006) found that soil pH can be affected by water drainage during fallow periodsⒸ ISERD

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IJERD – International Journal of Environmental and Rural Development (2013) 4-1

and rice straw inputs to the soil. Water drainage during the fallow season increases soil pH, whichmight explain higher pH readings in the sampled plots since it rained the night before sampling
occurred. Furthermore, the application of rice straw decreases soil pH, partly due to thedecomposition of organic matter. Since organic materials serve as an electron donor for soil
reduction, the soil pH decreases because of increased pressure from CO2 (Ponnamperuma et al.,
1966; Takuhito et al., 2006).
Soil coloration from the saline samples ranged from reddish yellow to strong brown, whilesamples from non-saline paddies were reddish yellow to pinkish gray. The majority of soil samples(60.29%) were classified as non-saline, except for one location (Table 1). Furthermore, themajority of soil samples had low nutrient contents (Tabel 2), including OM and N (less than 1%).
This finding is typical for soils in Northeast Thailand (Tulaphitak, 2002), partly due to loamy sandtexture, erosion, and land use activities. Only a few samples yielded moderate to high contents ofK. The independent samples t-tests showed significant differences of OM and total N contents
between non-saline soil and saline sites (mean difference = 0.127 and 0.006; p-value < 0.05,
respectively). Although no significant difference was detected, available K contents of saline soil
samples were higher than non-saline soils (Table 3). This may result from poor nutrient uptake
caused by dehydration since the rice plants were growing in saline soil (Patel et al., 2009).
Table 2  Soil properties: Total OM, Total N, Available P and K
Soil fertility
Moderate*
High*
Soil
Parameters
No. ofMean ± S.D.
No. ofMean ± S.D.
No. ofsalinity
samplessamplessamples(%)(%)(%)
NonOM (%)
0.44 ± 0.29
41 (100)
0 (0)
0 (0)
salineN (%)
0.02 ± 0.01
41 (100)
0 (0)
0 (0)
soil
P (ppm)0.11 ± 0.05
41 (100)
0 (0)
0 (0)
K (ppm)28.75±13.69
29 (71)70.22 ± 12.38
8 (20)
98.43 ± 6.81
4 (10)
SalineOM (%)
0.31 ± 0.22
27 (100)
0 (0)
0 (0)
soil
N (%)
0.02 ± 0.01
27 (100)
0 (0)
0 (0)
P (ppm)0.08 ± 0.08
27 (100)
0 (0)
0 (0)
K (ppm)19.79±10.87
22 (81)83.40 ± 0.44
3 (11)
255.55 ± 127.07
2 (7)Note: *Standards: Total OM (%): Low <1.5, Moderate 1.5-3.5, High >3.5; Total N (%): Low <0.3, Moderate 0.3-0.6,
High >0.6; Available P (ppm): Low <10, Moderate 10-25, High >25; and Available K (ppm): Low <60, Moderate
60-90, High >90
Source: Soil Survey Division, Land Development Department (1980)
Low*
Mean ± S.D.

Table 3 Comparison of soil nutrient contents between non-saline and saline soil samples
Group

N

Mean ± S.D.

Mean DifferenceNS410.437 ± 0.209
0.127
SS
27
0.310 ± 0.223
NS41
0.022 ± 0.0104
0.006
N (%)
SS
27
0.016 ± 0.0112
NS41
0.111 ± 0.054
0.030
P (ppm)SS
27
0.080 ± 0.075
NS41
43.638 ± 27.634-0.686K (ppm)SS
27
44.324 ± 69.526
Note: NS = non-saline soil sample and SS = saline soil sample
OM (%)

t-test (p-value)
2.354 (0.022)
2.349 (0.023)
1.943 (0.056)
ns

95% Confidence Interval of
the Difference
Lower
Upper
0.021
0.019
0.001
0.001
-0.001-0.0031-24.761-29.343

0.233
0.235
0.012
0.012
0.062
0.064
23.38927.970

Rice production and farm management in saline soil farming systems
Rain-fed rice cultivation is the primary occupation of Nong Due villagers. A total of 40 householdⒸ ISERD

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representatives (out of 70) participated in the survey. A majority of the households (n=34) had
encountered soil salinity issues (the averaged size was 0.89 ha/household which accounted for 34%
of their total paddy area). Primarily, farmers grow two rice cultivars including a glutinous mutant
of jasmine rice—RD6 and jasmine rice—KDLM-105. The average rice yield from farmers who
experienced soil salinity was 1.9 tons/ha, lower than the average production from non-saline
paddies (mean difference –113.39 kg/ha). Moreover, the size of saline paddies showed a negative
correlation with rice production (R2 = 0.120, p-value = 0.029).
The average household annual income derived from a four-person labor force wasapproximately 112,000 Baht (USD1 a 30.64 Baht as of December 14, 2012). These figures were
not significantly different between households that experienced soil salinity and those who did not.
Moreover, the household income and labor force did not show significant correlations with farmmanagement practices. Fertilizer application is likely dependent upon the availability of on-farmresources and word-of-mouth. Nonetheless, the total paddy field per household significantly
correlated with rice yields (R2 = 0.275, p-value = 0.001). Although this finding implies that thelabor force may not differ across samples, it does limit household production and management
abilities.
Rice production costs of farming systems which experienced soil salinity were estimated at
10,770 Baht/ha. The highest spending was associated with farm maintenance, especially fromfarmers using chemical fertilizers. The costs from non-saline farming locations were 9,791 Baht/ha,with 39.75% also spent on farm maintenance (Table 4). Seemingly, farmers have adapted to soil
salinity by using on-farm resources, such as cow manure, compost, and green manure. Farmers also
raised the height of paddy borders, so that more rainwater could be stored, thus ensuring that therice paddies were continuously submerged. Clermont-Dauphin et al. (2010) reported thatapproximately 20% of rice yields decreased because of salinity, but 87% decreased due to drought.
Therefore, water management is very important for rice cultivation, especially in saline paddies.
Table 4 Rice production and farm management information of sampled households
Information
1) Averaged size of total paddies (ha/household)2) Averaged size of saline paddies (ha/household)3)  Household’s  total  rice  production  (tons/ha)4) Income (Baht/household)5) Labor force (persons/household)6) Total costs of rice production (Baht/ha)
6.1) Land preparation and rice growing(transplanting and sowing)
6.2) Maintenance costs
6.2.1) Chemical fertilizer application
6.2.2) Manure application
6.2.3) Pesticide application
6.2.4) Organic fertilizer application
6.2.5) Rice husk & mulch application
6.3) Harvesting costs
Note: USD1 a 30.64 Baht as of December 14, 2012.

Households without saline
paddies (6 households)
2.74
2.0
133,000
4.06
9,791
3,095 (31.61%)

Households with saline
paddies (34 households)
2.63
0.89
1.9
108,000
3.50
10,7702,618 (24.31%)

3,892 (39.75%)
3,022 (77.64%)
548 (14.07%)
323 (8.29%)
2,804 (28.63%)

4,771 (44.30%)
2,775 (38.15%)
451 (9.46%)
64 (1.35%)
1,294 (27.11%)
187 (3.93%)
3,381 (31.39%)

CONCLUSION
Soil salinity is a prolonged issue for many farmers in Northeastern Thailand. Its distribution is
likely to expand if deforestation in recharge areas continues to occur. Despite the low correlation
between soil ECe and distance from saline plots to the closest vegetation, high salinity frequently
occurs in lower elevations and areas farther away from forest cover. Approximately 34% of the ricepaddies with soil salinity issues also encountered low soil nutrients. The average rice yield of
farmers experiencing soil salinity is lower than the productivity from non-saline paddies. Thisfinding illustrates that soil salinity negatively affects rice production. However, household income
and labor force did not show significant correlations with farm management practices. FertilizerⒸ ISERD

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IJERD – International Journal of Environmental and Rural Development (2013) 4-1

application is likely dependent on available on-farm resources and word-of-mouth. As long as soil
salinity remains an issue, then farmers will be forced to adapt. Use of on-farm resources, such as
cow manure, compost, and green manure are environmentally sensitive ways to reduce soil salinity.
Another effective strategy is raising the height of paddy borders, so that rainwater capture cancontinuously submerge the rice paddies.
ACKNOWLEDGEMENTSThe   authors   wish   to   thank   Nong   Due   village’s   leaders   and   all   villagers   who   participated   in   this  research project. Last but not least, the project could not be possible without the research grantfrom Khon Kaen University and Soil Problems in Northeastern Thailand Research Group, KKU.
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