**2. Climatic change and greenhouse gas emissions**

**Figure 1.** (a) Schematic diagram of methane production, oxidation, and emission from rice paddy field and (b) schematic

World rice production especially in Southeast Asia and tropical Asia is highly vulnerable to climate change. Rice production systems contribute to global climate change through emissions

O gases to the atmosphere and simultaneously

), and N<sup>2</sup>

), methane (CH<sup>4</sup>

90 Soil Contamination and Alternatives for Sustainable Development

emissions from rice paddy field.

diagram of N2

**1. Introduction**

of carbon dioxide (CO<sup>2</sup>

O, NO, and N<sup>2</sup>

Greenhouse gases (GHGs), mainly carbon dioxide (CO<sup>2</sup> ), methane (CH<sup>4</sup> ), and nitrous oxide (N2 O), have been contributing to about 80% to the current global radiative forcing [9]. Agricultural activities contribute to approximately 20% of the present concentrations of atmospheric GHGs [10], especially the emissions of CH<sup>4</sup> and N2 O from paddy fields [9]. Methane (CH4 ) and nitrous oxide (N2 O) are the two most important GHGs from agriculture, with global-warming potentials (GWP) of 25 and 298 CO<sup>2</sup> -equivalents, respectively, on a 100-year time horizon. Apart from the water vapor, CH<sup>4</sup> is a major greenhouse gas contributing 20% toward global warming with almost 25-fold higher global warming potential than carbon dioxide [11]. The concentrations of atmospheric CH<sup>4</sup> and N2 O have increased from 722 and 270 ppb in the pre-industrial period to 1853 and 328.9 ppb in 2016, respectively [12]. China, the largest rice-producing country, accounts for about 28% of global rice production [4] and the total CH4 and N2 O emissions from paddy fields are estimated to be 6.4 Tgyr−<sup>1</sup> and 180 Ggyr−<sup>1</sup> , respectively [13]. Although the global estimates of CH<sup>4</sup> emission from rice cultivation vary within 20–150 TgCH<sup>4</sup> year−<sup>1</sup> , the global average CH<sup>4</sup> is about 100 TgCH<sup>4</sup> year−<sup>1</sup> [14] and 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 understand the mechanism of CO2 , CH<sup>4</sup> , and N<sup>2</sup> O exchange and their main controlling factors for developing appropriate strategies to mitigate GHG emissions.

In paddy fields, the kinetics of the reduction processes are strongly affected by the composition and texture of soil and its content of inorganic electron acceptors. After flooding, microbial reduc-

<sup>−</sup>, Mn4+, Fe3+, and SO<sup>4</sup>

electron acceptors for their metabolic activities. Methane is produced at the terminal step under

soils. Soil Eh values decreased rapidly after flooding within 5–7 weeks then stabilized toward −200 to −240 mV and produced significant amount of methane [17]. High concentrations and fluxes of dissolved organic matter (DOM) in paddy soils from plant debris trigger microbial activity and thus the emission of greenhouse gases. Therefore, the objectives of this thematic topic are to highlight the feasible field management practices for sustainable rice production and recommend appropriate strategies to mitigate GHG emissions from paddy soils in the changing climate.

S, and CH<sup>4</sup>

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

(**Figure 2**). Microorganisms drive redox reactions in soil by using organic carbon and

**O emissions from the paddy field**

ing 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

O, N<sup>2</sup> , H<sup>2</sup>

anaerobic decomposition of organic matter and due to the reduction of CO<sup>2</sup>

 **and N2**

septum and transported to the laboratory for analysis of CH<sup>4</sup>

 **and N2**

l−<sup>1</sup>

The static closed chamber technique was used to measure CH<sup>4</sup>

<sup>2</sup>− as electron acceptors, accompanied

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

due to reduction-induced increasing

and N2

and N2

) was used for the ECD. Calibration was conducted with

O l−<sup>1</sup>

**O concentrations in the headspace air samples**

O concentrations in the headspace air samples were determined by a gas chro-

matograph (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>

centrations, respectively. Helium (99.9% purity) was used as a carrier gas (30 ml min−<sup>1</sup>

in He and 0.2, 0.6, and 1.0 μl N2

into CH4

in wetland

93

O emissions dur-

O concentrations by Gas

and N2

in He (CRM/RM Information

O con-

), and a

tion processes sequentially use NO3

by the emission of the trace gases N<sup>2</sup>

**4. Materials and methods**

**4.1. Measurement of CH4**

Chromatograph (**Figure 4**).

**4.2. Determination of CH4**

1.01, 7.99, and 50.5 μl CH4

make-up gas (95% argon and 5% CH<sup>4</sup>

Center of China) as primary standards.

CH4

and N2

pH-NH<sup>3</sup>
