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

Research article
erd

The Influence of Earthworm and Rice Stubble on Soil
Aggregate, Carbon Sequestration and Soil Fertility in
Sandy Loam Paddy Soil in Northeast Thailand
AJCHARAWADEE KRUAPUKDEE
Faculty of Agriculture, Khon Kaen University, Thailand
Email: ajchara_krua@hotmail.com, chuleemas1@gmail.com

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

MONGKON TA-OUN
Land Resources and Environment Section, Faculty of Agriculture
Khon Kaen University, Thailand
Received 16 December 2012

Accepted 30 January 2013(*Corresponding Author)

Abstract The objective of this study was to investigate the effect of epigeic earthworm(Eudrillus eugeniae) and rice stubble on soil aggregate, SOC, soil fertility and greenhousegases (CO2) emission in sandy loam paddy soils in Northeast Thailand. Experimental
design was a completely randomized design. There were four treatments of incubation
using Thai soil (Roi-et series) Sandy loam were: (I) soil control (no additions), (II) soil +rice stubble, (III) soil + earthworms (these added after 8 days incubation) and (IV) soil +rice stubble +  earthworms  (these  added  after  8  days’  incubation),  and  then  incubated  for  20 days. During the experiment, soil respiration (CO2), the aggregate size, SOC and soil
fertility (N, P and K) were measured. The results suggest that the treatment with adding
earthworms and rice stubble had significantly changed on soil aggregate than those
without earthworm and added rice stubble only. Earthworm increased SOC and soil
fertility (N, P and K) in paddy soil (sandy loam) than other treatment. The effect ofearthworm on the decomposition of rice stubble in paddy sandy loam may influence theCO2 emission from paddy soil.
Keywords sandy loam paddy soil, rice stubble, earthworm, carbon sequestration, soil
fertility

INTRODUCTION
Earthworms, one of the most important macroinvertebrates in the terrestrial ecosystems of thetemperate zone, exert important influences on soil functions (Fonte et al., 2007). Their activities
play an important role in improving and changing the physical, biological, and chemical properties
of soil (Coq et al., 2007). Earthworms improve the soil and increase water retention (Bossuyt et al.,2005). Additionally, the biomass and activity of soil microbial diversity (Doube and Beown, 1998)
encourage earthworm activity, and allow fungi to perform better. Such activities are the main
factors influencing the transformation of organic matter and are important for the dynamics ofcarbon in the soil. Thus, the experimental results of Don et al. (2008) reported that earthworms
have a significant impact on the turnover of carbon in soil. They assist nutrient cycling in soil
(Edwards and Bohlen, 1996).
Most of soil in Northeast Thailand is classified as sandy textured soil, which has relatively
low fertility (Patama et al., 2004). The change of land use from forest to agriculture causes soil
deterioration. Returning organic materials into the soil is one of the most effective approaches torestoring soil fertility (Patama et al., 2004). In Thailand, the main crop is rice. This contributes to ahigh amount of stubble and straw, while the rest of rice plant materials are retained in the paddyⒸ ISERD

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field. The rice residue produced is equal to 38.22 million tons/year (Rice Department, 2006). There
are several beneficial uses of rice residue, such as incorporating the residue into soil, which may
enhance soil fertility. Results of long-term research have shown that the carbon content of soil
treated with rice residue was low, while simultaneously, CO2 evolution increased (Samahadthai etal., 2010; Puttaso et al., 2011). There remains a critical need for research on the effects andinteractions (soil carbon dynamics and nutrient turnover) of earthworms with rice residue in agroecosystems (paddy fields).
OBJECTIVES
The objectives of this study were to investigate the activities of earthworms and added rice stubble
on soil properties; chemical, biological and physical; dynamics of organic carbon in soil and to
improve the properties of soil and increase carbon sequestration in soil.
METHODOLOGY
Soil samples were collected (0-15 cm depth) from paddy fields in Khon Kaen province, Northeast
Thailand. The soil textural class was sandy loam (62.40% sand, 36.60% silt, and 1% clay), organic
C 4.55 g kg-1, total N 0.28 g kg-1, available P 6.29 mg kg-1 and exchangeable K 38.51 mg kg-1.
After collection, the soil was air-dried and sieved to pass 2 mm. Residue, stones, and sand larger
than 2 mm. were discarded. Soil incubation consisted of 12 subsamples with four treatments, andthree replicates each. Treatments consisted of four categories: 1) non rice stubble with noearthworms 2) soil with added rice stubble 3) soil with added earthworms and 4) soil with added
rice stubble and earthworms. The earthworm species was Eudrilus eugeniae. The treatment added
rice stubble 1.15 g (2-3 cm) was mixed in 200 g soil and put in glass jars with lids. Moisture levels
in all treatments were appropriate (≈  70%)  and  incubated  at  30 oC. After seven days of incubation,eight adult earthworms were added in the designated earthworm treatments. Soil respirations were
measured at days: 0, 3, 7, 10, 14 and 18. At 20 days; earthworms were removed from the jars,
residues were discarded form soil, and the soil was air-dried. Soil was separated into two parts: onepart aggregately measured (sieving shaker), another part chemically measured. Organic carbon wasmeasured by the partial-oxidation method (Walkley and Black, 1934). Total nitrogen was measured
by micro Kjeldahl method (Jackson, 1975). Extractable phosphorous was determined by following
Olson’s  sodium  bicarbonate  extraction  method  (Olsen et al., 1954).
Exchangeable K was determined after extracting the sample using the ammonium acetate
extractable method, and analyzed using the Perkin Elmer model 3110 double beam atomic
absorption spectrophotometer (AAS) (Simard, 1993).
Analysis of variance pertaining to a complete random block design (CRD) and related
statistical analysis were performed employing Statistics 8.0 (Analytical Software, 2003). Mean
comparisons of different treatments were done by least significant difference (LSD) and standard
error of the difference (SED).
RESULTS AND DISCUSSION
Soil aggregate formation
The results of short term experimentation show the influence of earthworm activity on soil
aggregate formation in micro and macro aggregates (Table 1). The results clearly show that theearthworm significantly helped form new macroaggregates (p<0.01) on earthworm treatments
compared with added earthworms and no earthworms, or added rice stubble only. On the other
hand, activity of earthworm treatments decreased in the microaggregate. This is compatible withthe hierarchical theory of aggregate formation (Samahadthai et al., 2010; Tisdall and Oades, 1982).
In this experiment, added rice stubble had no effect on soil aggregate formation. Added earthwormsⒸ ISERD

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

had positive effects on soil aggregation. Earthworms contributed to soil aggregation mainly
through cast production and burrowing activities. Earthworm gut transit involved contaminationand mixing of soil, fragmentation of plant litter, and the addition of large amounts of water soluble
mucus (Edwards and Bohlen, 1996).
Table 1 Chang of soil aggregate after 20 days of incubation
with rice stubble and earthworm
Microaggregate
Macroaggregate(<1 mm.)(≤  2-1 mm.)Control (soil)
89.86 a9.63 cSoil + Rice stubble
83.13 a16.55 cSoil + Earthworm
72.33 b26.84 bSoil + Rice stubble + Earthworm
57.31 c41.82 af – test
**
**
CV %
5.41
16.43
Mean (n=3) in the same column followed by the same lower case letters are notsignificantly different at |p| ≤0.01  (LSD).
Land use system

Carbon sequestration in soil
Carbon storage was increased in all soils compared to the initial, by about 2-27% in all treatments(Table 2). Concentrations of total C in soil between added rice stubble with earthworm and added
rice stubble only were significantly (p<0.01) difference in soil organic C (SOC) than added
earthworm only (Table 2). Newly added of rice stubble residues was improved SOC. This results
were consistent with Naklang et al. (1999) which studied the management of chemical fertilizer
and rice straw and leaves in rain fed paddy fields of Northeast Thailand (in both the dry and rainyseason). They  reported  that  in  the  first  year’s  newly  added  residue  (1994),  the  incorporation  of  rice  stubble produced a higher level of organic carbon in soil (3.40 mg/g) than treatments without theincorporation of rice straw (3.10 mg/g). Interaction between earthworm activity and rice stubble
increased SOC 27.22% higher than the control. Earthworm activities on macroaggregate dynamics
are also important for C stabilization processes (Elliott, 1986; Six et al., 1998, 2002; Fonte et al.,2007). Due to rapid occlusion of organic materials, microbial communities associated withmicroaggregates within macroaggregates formed during or shortly after passage through theearthworm gut are relatively inactive, and therefore change relatively little over time compared tomacro aggregate populations as a whole (Mummey et al., 2006). Earthworm gut mixing with soil
was previously inaccessible as physically protected organic matter from microbial attack (Edwards
and Bohlen, 1996).
Table 2 Quantities of carbon in soil after 20 days of incubation
with rice stubble and earthworm
Total C
Changes in quantities(g kg-1 )relative to the control (%)
0.380 bControl (soil)
0.450 a18.55
Soil + Rice stubble
0.389 b
2.56
Soil + Earthworm
0.483
a
27.22
Soil + Rice stubble + Earthworm
f – test
**
CV %
6.28
Mean (n=3) in the same column followed by the same lower case letters are notsignificantly  different  at  |p|  ≤0.01  (LSD).
Treatment

Soil respiration
In this study, CO2 evolution was the highest in added rice stubble with earthworm treatment (Fig.
1). This demonstrates that rice stubble with earthworms could lead to a metabolically activeⒸ ISERD

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microbial biomass efficient in utilizing carbon resources. A greater proportion of substrate carbon
is lost in the form of CO2 through respiratory activity (Pang et al., 2012). Rice residues werecategorized as low quality organic material since they comprise a high content of carbon (367-423
g kg-1) and cellulose (353-507 g kg-1), and a low content of nitrogen (4.7–8.5 g kg-1) and lignin (1945 g kg-1). Incorporated into soils with optimum conditions, rice residues rapidly decomposed(Samahadthai et al., 2010; Puttaso et al., 2011) and led to an increase in CO2 evolution.

Fig. 1 Temporal pattern of CO2 evolution (g CO2 m2 day) as affectedby rice stubble and earthworm
Earthworm influence on N, P, K
In this experiment, the results have shown that the effect of earthworms and rice stubble increasesoil nutrients such as N, P and K. Ponnamperuma (1984) reported that rice straw added to soil
increases nitrogen, phosphorus, potassium and beneficial nutrients. Furthermore, rice straw helps
increase the amount of organic matter and nitrogen in the soil (IRRI, 1976). Utilization of ricestraw is possible through the incorporation of rice straw residue. Through cultivation into soil, ricestraw proves to be an important source of plant nutrients and improves soil fertility (Azam, 1990).
Concentration of total N, though not significant, increased through earthworm treatments(Table 3). Earthworms increase nitrogen mineralization via the biological processes or physicalchanges they bring about in the environment (Costello and Lamberti, 2012). Earthworm feeding
increases the rate at which organic N is mineralized into inorganic forms as earthworms primarily
excrete NH4+ (Scheu, 1987; Whalen et al., 2000; Costello and Lamberti, 2012). Concentration ofavailable P and exchangeable K were higher in rice stubble with earthworm treatment. Lui et al.,(2005) reported that during 100-day incubation periods, earthworm inoculation combined withorganic materials (rice straw, peanut residue and rape residue) increased significantly the content ofsoil available phosphorus. Basker et al., (1992) reported upon the incubation experiment ofTokomaru soil (silt loam) inoculated with the common pasture earthworm species Aporrectodea
caliginosa for a period of 21 days. The resulting content of exchangeable K increased significantly
due to earthworm activity.
Table 3 Chemical compositions of soil after 20 days incubation
with rice stubble and earthworm
Total N
Available P
Exchangeable K(mg kg-1)(mg kg-1)(mg kg-1)
0.28
6.83
c
42.39 dControl (soil)
0.29
7.81
b
118.74b
Soil + Rice stubble
0.42
7.11
bc
69.55
c
Soil + Earthworm
Soil + Rice stubble + Earthworm
0.45
11.78 a143.19 af – test
ns
**
**
CV %
51.62
4.67
2.46
Mean (n=3) in the same column followed by the same lower case letters are notsignificantly different at |p| ≤0.01 (LSD).
TreatmentⒸ ISERD

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CONCLUSION
This study suggests that the effect of earthworm and rice stubble increase soil fertility N, P and K
in paddy sandy loam. As, interaction between earthworm and rice stubble helped form newmacroaggregate; they are increased carbon storage compared to the initial, by about 2-27%. And
increase metabolically active microbial biomass and influence the CO2 emission from paddy soil.
Earthworms have an important in soil carbon sequestration. However, more studies need to be
conduct to investigate other factors may influence such as type of earthworm, soil and rice stubble
between agroclimatic zones.
ACKNOWLEDGEMENTS
This research was funding by Khon Kaen University Research fund, Integrate Water Resource
Management Research and Development Center in Northeast Thailand, GWRC and the office ofHigher Education Commission and Khon Kaen University under the   research   project   “AgroIndustrial Waste Management and Utilization”  and  thanks  to  Prof.  Dr. Machito MIHARA for kind
support. Thanks   to   “Problem   Soil   Research   Group”   and   research   project   “Using   Soil   Biota   for  Biological Monitoring and Ecological Zoning in the Salt-Affected Area in Northeast Thailand.
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