**8. Measurements techniques of methane emission from paddy field**

Recently, scientists are applying several techniques for measuring the CH4 emission from the paddy field.

### **8.1 Closed chamber method**

The most common technique for measuring the CH4 emission in the rice paddy field is the closed chamber method (**Figure 7**) [24]. Normally, the chamber made of plexiglass (size: 50 cm length × 50 cm width × 100 cm height). The chamber equipped with a fan to make sure the inside gas mixing during chamber deployment. The chamber basement equipped with a water seal. Gas sampling needs to do simultaneously at three points per plot once a week. Normally, gas samples collect at 0, 5, 10, 20, and 30 min after the chamber deployment between 7:00–10:00 am. The samples taken by a syringe and store in evacuated glass vials and then subjected to the laboratory analysis using gas chromatography. The best hour for representing average daily flux is when temperatures are close to the daily mean, i.e., at 10 a.m. This is the best way to estimate the daily cumulative value from a unique measurement of the day [67]. The main advantages of this method are detecting low fluxes, of being easy to manipulate, low costs and flexibility [78].

#### **8.2 Eddy covariance method using an open-path gas analyzer**

The eddy covariance method is a complex, expensive and advanced method for measuring the CH4 emission from the real-life rice paddies (**Figure 8**). The eddy covariance method calculates fluxes of a scalar of interest (i.e. CH4, CO2, LE, and H) at the same time, measuring turbulent fluctuations in vertical wind speed and the scalar and then computing the covariance between the two [79]. A sonic anemometer-thermometer (CSAT3) measures three-dimensional wind speed and sonic temperature. An openpath CO2/H2O gas analyzer (LI-7500A) measures fluctuations in CO2 and water vapor densities and an open-path CH4 analyzer (LI-7700) measures CH4 concentrations [79]. CSAT3, the point of reference, has to fix at certain meters above the ground. The data from CSAT3, LI-7500A, and LI-7700 sampled at 10 Hz using a data logger (CR3000). The eddy covariance raw data need to process and quality control use EddyPro software to compute the fluxes of CH4, CO2, LE, and H over a 30-minute interval.

Eddy covariance can give a better picture of how much CH4 real-life rice paddies are emitting, for example, detect and quantify CH4 from rice paddies [80]. Compare

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**Figure 8.**

*LI-7700 open-path CH4 analyzer.*

**Figure 7.**

*Methane Cycling in Paddy Field: A Global Warming Issue*

*The closed chamber technique of CH4 sampling in rice planted paddy field.*

*Set-up of eddy covariance system with CSAT3 sonic anemometer, LI-7500A open-path CO2/H2O analyzer, and* 

*DOI: http://dx.doi.org/10.5772/intechopen.94200*

#### **Figure 7.**

*The closed chamber technique of CH4 sampling in rice planted paddy field.*

#### **Figure 8.**

*Set-up of eddy covariance system with CSAT3 sonic anemometer, LI-7500A open-path CO2/H2O analyzer, and LI-7700 open-path CH4 analyzer.*

with an open-path and a closed path CH4 analyzer to provide advances in understanding the performance and limitations of the eddy covariance method applied to CH4 measurements, from an instrumental and flux processing point of view. Closed-path CH4 analyzers require high flow rates for significantly reduced optical cell pressures to provide adequate response time and sharpen absorption features [81]. Closed path CH4 analyzer can detect low fluxes and it is less expensive and flexible, on the other hand, the eddy covariance method using an open-path gas analyzer is highly sensitive, expensive and complex but gets a better estimation of CH4 flax from paddies [82].

### **8.3 The calculation of the total methane emission (ECH4)**

The CH4 can be calculated by following Equation (1).

$${}^{E}\text{CH}\_{4}\left(=E\_{plunt} + E\_{luubble} + E\_{diffusion}\right) \tag{1}$$

At first, Eplant is given by.

$$\mathbf{E}\_{\rm planet} = \mathbf{k}\_{\rm p} \times \mathbf{k}\_{\rm tp} \times \mathbf{J}\_{\rm root} \times \mathbf{LAI} \times \mathbf{C}\_{\rm CH4soil} \,\mathrm{\,\,t} \tag{2}$$

Where kp is the turnover rate of the methane emission via rice plant (=0.03 day−1), ∫tp is a factor of CH4 emission defined for each paddy type (=15.0), ∫root is a distribution factor of rice root in the soil, and LAI is the leaf area index (m<sup>2</sup> m−2).

Ebubble is given by.

$$\mathbf{E}\_{\text{bubble}} = \mathbf{k}\_{\text{b}} \times \left( \mathbf{C}\_{\text{CH4coll}} \text{ - C}\_{\text{threshold}} \right), \tag{3}$$

Where kb is a turnover rate of the CH4 emission as bubble (=1.0 day−1), and Cthresh is the dissolved CH4 threshold at which CH4 bubble formation occurs (=6.0 gC m−3).

Ediffusion is given by,

$$\mathbf{E}\_{\text{diffusion}} = \left(\mathbf{C}\_{\text{CH4wall}} - \mathbf{C}\_{\text{CH4ram}}\right) \times \left[\_{\text{dif}} \times \left[\_{\text{tor}} \times \mathbf{p}\_{\text{soll}}\right] \tag{4}$$

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soil.

*Methane Cycling in Paddy Field: A Global Warming Issue*

up to 37.5% in Indonesia [86] and 40% in India [87].

potential mitigation option [91].

**10. Conclusions**

sustain rice production.

ment conditions.

global warming.

before harvest [53]. Higher yielding rice genotypes could be viable options for reducing the release of CH4 from paddy fields to the atmosphere [13]. System of Rice Intensification (SRI) is the alternative rice farming for climate change adaptation and mitigates greenhouse gas emission from paddy fields. The study showed that the SRI paddy field with intermittent wetting-drying irrigation reduced CH4 emission by up to 32% [84]. SRI application can save water irrigation up to 28%, 38.5% and 40% in Japan, Iraq and Indonesia, respectively [85]. SRI also reduced greenhouse gas emission that is represented by reducing global warming potential

The activity of CH4 producing bacteria is inhibited from the oxidizing condition of paddy soil by water management. CH4 emission factor for intermittently flooded paddy fields can decrease by approximately 20% [88]. Water management and organic material management are significant for reducing CH4 emissions from rice paddy fields. Mid-season drainage and intermittent flooding are effective for increasing the productivity and quality of rice as well as reducing CH4 emissions. Mitigation of CH4 emissions from rice paddy fields by water management has huge potential to be marketed. A field experiment in the Philippines showed that direct seeding techniques reduced CH4 emissions by 18% as compared with transplanted rice. Another study, in Japan, showed that global warming potential declined by 42% just by changing the puddle of rice seedlings to zero tillage. Moreover, CH4 emission can be reduced by shifting to more heat-tolerant rice cultivars and by adjusting sowing dates. It will also prevent yield decline due to temperature increases [89]. A multi-criteria evaluation ranking score for CH4 mitigation strategy is been done in Egypt. They found that short duration rice varieties got the highest score. This strategy could be reduced 25% of CH4 emission, reduce 20% of water consumption without any reduction in rice productivity. On the other hand, fertilizer management strategy was in the second-ranking and followed by the midseason drainage [90]. The heat-tolerant improved rice variety with low CH4 emission is a

The most important aim of studies on CH4 emission from paddy fields is the mitigation of global warming and adaptation with climate change. CH4 emission is controlled by several factors such as temperature, soil pH, Eh, rice cultivar, root, rhizosphere, group of methanogens, paddy growing stages and field management. From the above-mentioned discussion, it is clear how CH4 cycling in paddy fields, also how much CH4 release to atmosphere and leached to ground water and

CH4 can be reduced from paddy field through management practices like, the mid-season drainage, alternate wetting, drying irrigation and using alternative fertilizers have been shown to reduce CH4 emissions from rice paddies and achieve

By using a combination of feasible mitigation technologies there is great potential to reduce CH4 emission from rice fields and increase rice production. Crop improvement strategies such as breed high yielding and high stress tolerant rice varieties with reduced CH4 emissions will help the CH4 mitigation. These rice varieties should be adaptable to changing climate e.g., the stress and water manage-

Cultivation of high-yielding and more heat-tolerant rice cultivars will be a promising approach to reduce CH4 emissions from paddy fields and slowing down

*DOI: http://dx.doi.org/10.5772/intechopen.94200*

Where CCH4 atm is the atmospheric CH4 concentration (=1.0 × 10–3 gC m-3), ∫dif is a diffusion coefficient of CH4 (=1.73 × 10−4 m2 day−1), ∫tor is a tortuosity coefficient of the soil (=0.66), and psoil is the soil porosity defied for each soil type (mm mm−1).
