**4. Materials and methods**

**Figure 2.** Paddy soil redox status, sequential reduction and oxidation of inorganic nitrogen, manganese, and iron in

O emissions from paddy fields are estimated to be 6.4 Tgyr−<sup>1</sup>

, the global average CH<sup>4</sup>

may increase further due to the expansion of rice cultivation as well as intensification of rice agriculture for the increasing world population [15]. Therefore, it is very important to under-

Paddy soils are mostly alluvial soils and low humic gley soils (or Entisols and Inceptisols). In addition, vertisols, reddish-brown earths or Alfisols, red-yellow podzolic soils or Ultisols, and latosols or Oxisols are utilized for paddy rice cultivation. Paddy soils are found mainly on alluvial lands such as deltas and flood plains of big rivers, coastal plains, fans, and lower terraces. In general, paddy soils are resistant to erosion when they are terraced and there are ridges around the field, as measures to retain surface water. Paddy fields in the lowlands receive new sediments deposited from run-off that carries eroded topsoil down from the uplands, thus sustaining soil fertility and productivity. The paddy soils have medium to high organic matter (1.5–3.97 g/kg), available phosphorus (11.7–19.9 mg/kg), available potassium (61.6–132.9 mg/kg), and cation exchange capacity (15.5–33.1 cmol/kg). The most common practice in paddy rice cultivation is flooding or temporary water logging of the land surface. Soil redox potential (Eh) or electron activity in soil gradually decreases after flooding, which causes significant methane production at around −200 mV [16], and creates high risk of gaseous N losses through denitrification (**Figure 2**).

and 180

[14] and

emission from rice cultivation

year−<sup>1</sup>

is about 100 TgCH<sup>4</sup>

O exchange and their main controlling factors for

flooded soil, and methane gas formation [16].

the total CH4

Ggyr−<sup>1</sup>

and N2

92 Soil Contamination and Alternatives for Sustainable Development

vary within 20–150 TgCH<sup>4</sup>

stand the mechanism of CO2

**3. Characteristics of paddy soils**

, respectively [13]. Although the global estimates of CH<sup>4</sup>

, and N<sup>2</sup>

year−<sup>1</sup>

, CH<sup>4</sup>

developing appropriate strategies to mitigate GHG emissions.

#### **4.1. Measurement of CH4 and N2 O emissions from the paddy field**

The static closed chamber technique was used to measure CH<sup>4</sup> and N2 O emissions during rice growing period [18]. The chambers were made of PVC and consisted of two parts: an upper transparent compartment (100 cm height, 30 cm width, and 30 cm length) was placed on a permanently installed bottom collar (10 cm height, 30 cm width, and 30 cm length). Three replicate chambers were used. Each of these chambers was placed in each plot. Each chamber was installed with a battery-operated fan to homogenize the air inside the chamber headspace, a thermometer to monitor temperature changes during the gassampling period, and a gas-sampling port with a neoprene rubber septum at the top of the chamber for collecting gas samples from the headspace. Gas samples were collected twice daily (**Figure 3**), sampling during 9.00 am to 12.00 and 12.30 pm to 3.30 pm. A 100-mL plastic syringe equipped with a 3-way stopcock was used to collect gas samples from the chamber headspace 0, 15, and 30 min after chamber deployment. Gas samples were collected twice a day. The collected gas samples were immediately transferred to 100-mL air-evacuated aluminum foil bags (Delin Gas Packaging Co., Ltd., Dalian, China) sealed with a butyl rubber septum and transported to the laboratory for analysis of CH<sup>4</sup> and N2 O concentrations by Gas Chromatograph (**Figure 4**).

#### **4.2. Determination of CH4 and N2 O concentrations in the headspace air samples**

CH4 and N2 O concentrations in the headspace air samples were determined by a gas chromatograph (Shimadzu GC-2014, Kyoto, Japan) packed with a Porapak Q column (2 m length, 4 mm OD, 80/100 mesh, stainless steel column) (**Figure 4**). A flame ionization detector (FID) and an electron capture detector (ECD) were used for the determination of CH<sup>4</sup> and N2 O concentrations, respectively. Helium (99.9% purity) was used as a carrier gas (30 ml min−<sup>1</sup> ), and a make-up gas (95% argon and 5% CH<sup>4</sup> ) was used for the ECD. Calibration was conducted with 1.01, 7.99, and 50.5 μl CH4 l−<sup>1</sup> in He and 0.2, 0.6, and 1.0 μl N2 O l−<sup>1</sup> in He (CRM/RM Information Center of China) as primary standards.

The total CH<sup>4</sup>

or N2

**4.4. Estimation of GWPs of CH<sup>4</sup>**

) + (298 × N<sup>2</sup>

**5. Results and discussion**

are presented in **Table 1.**

stimulating CH4

as well as CH4

GWP by grain yield for rice [20, 21].

To estimate the GWP, CO<sup>2</sup>

in emission of CH4

(25 × CH<sup>4</sup>

oxide emissions in all growth stages of rice crop.

**Figure 4.** Injecting air samples into GC for determination of CH<sup>4</sup>

and N2

O)], kg CO<sup>2</sup>

Azolla-cyanobacteria significantly decreased CH<sup>4</sup>

ments (**Table 2**) [18]. Seasonal cumulative CH<sup>4</sup>

and Bangladesh decreased seasonal cumulative N<sup>2</sup>

 **and N2 O**

O is converted into "CO2


this study, we used the IPCC factors to calculate the combined GWPs for 100 years [GWP =

tural practices. In addition, the greenhouse gas intensity (GHGI) was calculated by dividing

The mean rice statistics and cumulative methane emissions in the rice producing countries

It is known that China, India, Indonesia, Bangladesh, and Vietnam have been playing a dominating role in total rice production (**Table 1**), which may impose a threat to the environment by

facturing industry, is a feasible soil amendment to supplement mainly calcium and sulfur for

methanogens. It was reported that silicate slag and phospho-gypsum in combination with

status (**Figure 5**) [18, 23]. Ali et al. reported that biochar amendments in paddy soils of Japan

tively, followed by 26.3 and 25.0% reduction with biochar plus Azolla-cyanobacteria amend-

significantly decreased due to Azolla-cyanobacterial inoculation with phospho-gypsum and

rice cultivation. The high content of sulfate in phospho-gypsum might prevent CH<sup>4</sup>

O emission from paddy fields was the summation of methane and nitrous

Management of Paddy Soil towards Low Greenhouse Gas Emissions and Sustainable Rice…

and N2

from CH4

emissions. Phospho-gypsum, a by-product of the phosphate fertilizer manu-

emissions due to stronger competitor for substrates (hydrogen or acetate) than

is typically taken as the reference gas, and an increase or reduction

O concentrations.

and N2


http://dx.doi.org/10.5772/intechopen.83548

95

flux while improved rice rhizospheric redox

emissions and global warming potentials were

O emissions by 31.8 and 20.0%, respec-

O under various agricul-

formation

**Figure 3.** (A) Prototype and (B) gas sampling in rice planted paddy field through the closed chamber technique [18].

#### **4.3. Estimation of CH4 and N2 O fluxes, GWPs, and greenhouse gas intensity (GHGI)**

CH4 and N2 O fluxes from the paddy field were expressed as the increase/decrease in CH<sup>4</sup> and N2 O mass per unit surface area per unit time. CH4 and N2 O fluxes were estimated by the following equation [19]: *F* = *MV*\**dc*/*dt*\**H*\*(273/(273 + *T*); where *F* is the CH4 or N2 O flux (mg CH4 m−<sup>2</sup> h−<sup>1</sup> or μgN2 O m−<sup>2</sup> h−<sup>1</sup> ), *M* is the molar mass of the respective gas (16 for CH<sup>4</sup> and 44 for N2 O), *V* is the molar volume of air at a standard state (22.4 l mol−<sup>1</sup> ), *dc/dt* is the change in headspace CH4 and N2 O concentration with time (μmolmol h−<sup>1</sup> ), *H* is the height of the chamber above the water surface (m), and *T* is the air temperature inside the chamber (°C). Management of Paddy Soil towards Low Greenhouse Gas Emissions and Sustainable Rice… http://dx.doi.org/10.5772/intechopen.83548 95

**Figure 4.** Injecting air samples into GC for determination of CH<sup>4</sup> and N2 O concentrations.

The total CH<sup>4</sup> or N2 O emission from paddy fields was the summation of methane and nitrous oxide emissions in all growth stages of rice crop.

#### **4.4. Estimation of GWPs of CH<sup>4</sup> and N2 O**

To estimate the GWP, CO<sup>2</sup> is typically taken as the reference gas, and an increase or reduction in emission of CH4 and N2 O is converted into "CO2 -equivalents" by means of their GWPs. In this study, we used the IPCC factors to calculate the combined GWPs for 100 years [GWP = (25 × CH<sup>4</sup> ) + (298 × N<sup>2</sup> O)], kg CO<sup>2</sup> -equivalents ha−<sup>1</sup> from CH4 and N2 O under various agricultural practices. In addition, the greenhouse gas intensity (GHGI) was calculated by dividing GWP by grain yield for rice [20, 21].

## **5. Results and discussion**

**4.3. Estimation of CH4**

or μgN2

and N2

m−<sup>2</sup> h−<sup>1</sup>

in headspace CH4

CH4

CH4

for N2

and N2

 **and N2**

94 Soil Contamination and Alternatives for Sustainable Development

O m−<sup>2</sup> h−<sup>1</sup>

and N2

O mass per unit surface area per unit time. CH4

following equation [19]: *F* = *MV*\**dc*/*dt*\**H*\*(273/(273 + *T*); where *F* is the CH4

O), *V* is the molar volume of air at a standard state (22.4 l mol−<sup>1</sup>

**O fluxes, GWPs, and greenhouse gas intensity (GHGI)**

and N2

), *M* is the molar mass of the respective gas (16 for CH<sup>4</sup>

O fluxes were estimated by the

or N2

), *dc/dt* is the change

), *H* is the height of the

O flux (mg

and 44

O fluxes from the paddy field were expressed as the increase/decrease in CH<sup>4</sup>

O concentration with time (μmolmol h−<sup>1</sup>

chamber above the water surface (m), and *T* is the air temperature inside the chamber (°C).

**Figure 3.** (A) Prototype and (B) gas sampling in rice planted paddy field through the closed chamber technique [18].

The mean rice statistics and cumulative methane emissions in the rice producing countries are presented in **Table 1.**

It is known that China, India, Indonesia, Bangladesh, and Vietnam have been playing a dominating role in total rice production (**Table 1**), which may impose a threat to the environment by stimulating CH4 emissions. Phospho-gypsum, a by-product of the phosphate fertilizer manufacturing industry, is a feasible soil amendment to supplement mainly calcium and sulfur for rice cultivation. The high content of sulfate in phospho-gypsum might prevent CH<sup>4</sup> formation as well as CH4 emissions due to stronger competitor for substrates (hydrogen or acetate) than methanogens. It was reported that silicate slag and phospho-gypsum in combination with Azolla-cyanobacteria significantly decreased CH<sup>4</sup> flux while improved rice rhizospheric redox status (**Figure 5**) [18, 23]. Ali et al. reported that biochar amendments in paddy soils of Japan and Bangladesh decreased seasonal cumulative N<sup>2</sup> O emissions by 31.8 and 20.0%, respectively, followed by 26.3 and 25.0% reduction with biochar plus Azolla-cyanobacteria amendments (**Table 2**) [18]. Seasonal cumulative CH<sup>4</sup> emissions and global warming potentials were significantly decreased due to Azolla-cyanobacterial inoculation with phospho-gypsum and


silicate slag amendments [18]. Combined effects of blast furnace slag and revolving furnace

Silicate slag and biochar amendments in different soils of Japan also reduced cumulative CH<sup>4</sup>

The IPCC 4th Assessment Report (IPPC) states that Southeast Asia is expected to be seriously affected by the adverse impacts of climate change [11]. The frequency of floods, drought, cyclones, tornadoes, thunderstorm, and earthquake increased during the last 5 years, which badly affected the natural vegetation and forest covers, wild animals, wetlands, and land resources, and ultimately, agricultural productivity declined. In Indonesia, the Philippines, Thailand, and Vietnam, the annual mean temperatures are projected to rise by 4.8°C by 2100, and the global mean sea level will increase by 70 cm during the same period [24]. It has been reported that in Southeast Asia, small changes in the annual rainfall are expected to continue up to 2040 [25], and there will be an increase in the occurrence of severe weather including heat waves and precipitation events. Increases in tropical cyclone intensities by 10–20% are

emission rates (**Figure 1**). Silicate slag and phospho-gypsum

O emissions, global warming potentials (GWPs), and yield scaled GHG intensity

O emission rates compared to control treatment (NPK), although no

Management of Paddy Soil towards Low Greenhouse Gas Emissions and Sustainable Rice…

O emission rates (**Figure 6**);

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97

slag amendments also showed decreasing effects on GWPs (**Table 2**).

flux, while increased rice growth and yield parameters (**Table 3**) [23].

Among the amendments, biochar significantly decreased N<sup>2</sup>

significant differences were observed (**Figure 6**) [18].

**5.1. Climate change and threats to rice production**

however, it increased CH<sup>4</sup>

amendments lowered N2

**Table 2.** Cumulative seasonal CH4

under different soil amendments. Source: [18, 23].

and N2

**Table 1.** Mean rice statistics (2004–2014) in the main rice producer countries in Asia, Latin America, and the Caribbean (LAC).

**Figure 5.** Trends of CH<sup>4</sup> flux and soil Eh with different soil amendments during rice cultivation in Bangladesh, Japan, and Korea [18, 23].

silicate slag amendments [18]. Combined effects of blast furnace slag and revolving furnace slag amendments also showed decreasing effects on GWPs (**Table 2**).

Silicate slag and biochar amendments in different soils of Japan also reduced cumulative CH<sup>4</sup> flux, while increased rice growth and yield parameters (**Table 3**) [23].

Among the amendments, biochar significantly decreased N<sup>2</sup> O emission rates (**Figure 6**); however, it increased CH<sup>4</sup> emission rates (**Figure 1**). Silicate slag and phospho-gypsum amendments lowered N2 O emission rates compared to control treatment (NPK), although no significant differences were observed (**Figure 6**) [18].

### **5.1. Climate change and threats to rice production**

The IPCC 4th Assessment Report (IPPC) states that Southeast Asia is expected to be seriously affected by the adverse impacts of climate change [11]. The frequency of floods, drought, cyclones, tornadoes, thunderstorm, and earthquake increased during the last 5 years, which badly affected the natural vegetation and forest covers, wild animals, wetlands, and land resources, and ultimately, agricultural productivity declined. In Indonesia, the Philippines, Thailand, and Vietnam, the annual mean temperatures are projected to rise by 4.8°C by 2100, and the global mean sea level will increase by 70 cm during the same period [24]. It has been reported that in Southeast Asia, small changes in the annual rainfall are expected to continue up to 2040 [25], and there will be an increase in the occurrence of severe weather including heat waves and precipitation events. Increases in tropical cyclone intensities by 10–20% are


**Table 2.** Cumulative seasonal CH4 and N2 O emissions, global warming potentials (GWPs), and yield scaled GHG intensity under different soil amendments. Source: [18, 23].

**Figure 5.** Trends of CH<sup>4</sup>

Source: M indicates million [22].

(LAC).

and Korea [18, 23].

flux and soil Eh with different soil amendments during rice cultivation in Bangladesh, Japan,

**Country Harvested area (Mha) Total production (Mt) Yield (kg ha−<sup>1</sup>**

96 Soil Contamination and Alternatives for Sustainable Development

India 43 146 43,400 110.1 China 29 195 6500 180 Indonesia 12 63 4900 210 Bangladesh 11 46 4200 100 Vietnam 7 40 5300 180 Brazil 2 12 44,300 60 Colombia 0.5 2 4600 210 Peru 0.4 3 7200 240 Argentina 0.2 1 6600 280 Uruguay 0.2 1 7600 280

**Table 1.** Mean rice statistics (2004–2014) in the main rice producer countries in Asia, Latin America, and the Caribbean

**) CH4**

 **emission(kg ha−<sup>1</sup>**

**)**


**Table 3.** Rice plant growth, yield components, and cumulative CH<sup>4</sup> flux under biochar and silicate amendments in different field sites of Japan. Source: JSPS Report by Ali [23].

**Figure 6.** Trends of N<sup>2</sup> O flux and DO concentrations under different soil amendments during rice cultivation in Bangladesh, Japan, and Korea [18].

**Treatments**

**Flood water paddy field (Showair Union)**

**Grain** 

**Straw** 

**Gross** 

**Total** 

**Net** 

**BCR**

**Grain** 

**Straw** 

**Gross** 

**Total** 

**Net** 

**BCR**

**yield** 

**yield** 

**return** 

**variable cost** 

**return** 

**Tk./ha**

**(kg/ha)**

**(kg/ha)**

**(Tk./ha)**

**(Tk./ha)**

**yield** 

**yield** 

**return** 

**variable cost** 

**return** 

**(Tk./ha)**

**(kg/ha)**

Control (no top dressing, no

2143

4146

44,940

30,333

14,606

1.48

2106

4126

44,196

30,266

13,930

1.46

ducklings)

NPKS (100%) +

NPKS (50%) +

oyster shell + ducklings

NPKS (50%) +

+ ducklings

NPKS (50%) + azolla-

2650

5283

105,641

48,333

57,308

2.20

2603

5183

102,658

48,334

54,325

2.14

cyanobacterial mixture +

duckling

Significance level

**Table 4.**

\*\*

\*\*

\*\*

\* Overall productivity of rice duck farming in wetland paddy ecosystem of Dingaputa Haor, Netrokona district by Ali [28].

\*

\*

\*

\*

\*

\*

\*

\*

Management of Paddy Soil towards Low Greenhouse Gas Emissions and Sustainable Rice…

http://dx.doi.org/10.5772/intechopen.83548

99

vermicompost

2776

5516

108,291

50,733

57,558

2.14

2693

5370

104,551

47,400

57,151

2.20

bioslurry with

2446

4850

101,358

49,750

51,608

2.04

2433

4883

99,108

49,750

49,558

2.0

ducklings

2576

5106

104,086

49,450

54,636

2.12

2496

4840

100,353

49,450

50,903

2.04

**(kg/ha)**

**(Tk./ha)**

**(Tk./ha)**

**Flood water paddy field (Tetulia Union)**


**Table 3.** Rice plant growth, yield components, and cumulative CH<sup>4</sup>

different field sites of Japan. Source: JSPS Report by Ali [23].

98 Soil Contamination and Alternatives for Sustainable Development

**Figure 6.** Trends of N<sup>2</sup>

Bangladesh, Japan, and Korea [18].

flux under biochar and silicate amendments in

O flux and DO concentrations under different soil amendments during rice cultivation in

**Table 4.** Overall productivity of rice duck farming in wetland paddy ecosystem of Dingaputa Haor, Netrokona district by Ali [28]. anticipated, and temperatures are projected to continue to increase by about 0.7–0.9°C [25]. Furthermore, sea levels have risen by 1–3 mm/year, marginally higher than the global average [24]. Rice production systems of this region have become increasingly threatened by the effects of climate change as a large portion of the rice-growing areas are located in especially vulnerable regions. A decrease of 10% in rice yield has been found to be associated with every 1°C increase in temperature [24], while the yield of dry-season rice crops in the Philippines decreased by as much as 15% for each 1°C increase in the growing season mean temperature. These temperature and aggravating climate change effects may cause a decline in the world rice production, which have already shown negative effects on agricultural production. By 2100, Indonesia, the Philippines, Thailand, and Vietnam are projected to experience a potential fall of about 50% in rice yield due to the occurrence of extreme climatic events [24, 26]. Furthermore, rice yield would be affected severely due to sea level rise and intrusion of saline water in the coastal area, which will hamper rice growth and yield. Rising sea levels in association with heavy monsoon rainfall will create serious waterlogging and prolonged stagnant floods in major rice-growing, low lying mega-deltas in Southeast Asia, which ultimately deteriorate rice production in the deltas since only a few low-yielding rice varieties have evolved to withstand such conditions [27]. The recent natural disasters such as flash floods caused by water of Indian Meghalaya state and excessive rainfall in the low lying ha or areas of Bangladesh [28] badly affected the only cultivated rice crop, the Boro rice (winter rice), at this region; however, due to rice duck mixed farming, the overall productivity and net profit were recovered to some extent (**Table 4**).

seeding instead of transplanting resulted in a 16–54% reduction in CH<sup>4</sup>

direct-seeded rice (9.0 Mg ha−<sup>1</sup>

tion technique increased the N<sup>2</sup>

the direct seeded rice production system.

Water management influences rice yield and CH<sup>4</sup>

cumulative CH4

**emissions**

**systems**

eq ha−<sup>1</sup>

CO2

may cause more CH4

eq Mg−<sup>1</sup>

as N2

to N2

) than that of traditional cultivation (4186 kg CO<sup>2</sup>

emission was more significantly reduced under dry-direct seeding compared to wet-direct seeding. However, grain yield in direct seeded rice (DSR) was found lower than Puddle transplanted rice (PTR), probably due to poor crop stand, high percentage of panicle sterility, and higher weed and root-knot nematode infestation [33]. It was also observed that grain yield of

Average yield penalty of around 10% was observed for the direct seeded rice (DSR) compared with puddle transplanted rice [34]. It was reported [35] that over the rice-growing season,

systems. Irrigated rice fields are an integral part of the rice production system in Asian countries, which contribute about 75% to global rice production. Single or multiple drainages

compared to those observed under continuous flooding systems [36, 37]. Mid-season drainage and intermittent flooding were found effective for increasing productivity and quality of rice as well as reducing methane emissions in Japan [38]. The AWD field showed the same yield as continuous flooded field, but saved 16–24% in water costs and 20–25% in production costs. Most farmers in China, Japan, and South Korea have been practicing this mid-season drainage (5–7 days dry out) to increase rice yield and decrease GHG emissions. Mid-season drainage and intermittent irrigations may reduce methane emissions by about 50%. It was also reported [39] that the AWDI treatment (irrigation applied when water level in the pipe

fell 15 cm) showed superiority for the rice yield performance and seasonal CH<sup>4</sup>

**6.4. Diverse farm management practices, soil amendments, and rice cropping** 

reduction, water savings, and maximum water productivity index. However, the AWD irriga-

Feasible management approaches based on agroecosystem have to be adopted to sustain agricultural productivity in the changing climatic conditions. For example, the ground cover rice production system (GCRPS), through which paddy soils are covered by thin plastic films to conserve soil moisture nearly at saturated status, is a promising technology to increase yields with less irrigation water. However, increased soil aeration and temperature under GCRPS

reported that the GHG emissions for the ground cover rice production system (GCRPS, i.e., paddy soils being covered by thin plastic film) were found significantly lower (1973 kg CO<sup>2</sup>

sions under GCRPS were on average 80% lower as compared to the traditional rice cultivation. The yield-scaled GHG emissions from GCRPS were further reduced from 377 to 222 kg

intensification (SRI), an agro-ecological methodology, could be a feasible technique to sustain

O emission by 97%, especially in DS [40].

O emissions compared to conventional techniques. Yao et al. [41]

eq ha−<sup>1</sup>

O emissions greatly decreased while yields increased. The system of rice

). Total seasonal CH<sup>4</sup>

**6.3. Water management for sustainable rice production and minimizing GHG** 

during a rice growing season (e.g., AWD) are reported to reduce CH<sup>4</sup>

) was identical to grain yield of transplanted-flooded rice [34].

emissions were significantly higher in puddle transplanted rice compared to

Management of Paddy Soil towards Low Greenhouse Gas Emissions and Sustainable Rice…

and N2

emission [32]. CH4

101

http://dx.doi.org/10.5772/intechopen.83548

O emissions from rice cultivation

emissions by 48–93%

emission

emis-
