1. Greenhouse Gas Emission
Agriculture is both a victim of and a contributor to climate change. On the one hand, agricultural activities
contribute approximately 30 percent of total greenhouse gas emissions, mainly due to the use of chemical
fertilizers, pesticides, and animal wastes. This rate is bound to rise further because of an increase in the demand
for food by a growing global population, the stronger demand for dairy and meat products, and the
intensification of agricultural practices. On the other hand, these greenhouse gases include nitrous oxide (N2O),
carbon dioxide (CO2), and methane (CH4), which all contribute to climate change and global warming and
thereby have a profound impact on the sustainability of agricultural production systems. Methane and nitrous
oxide emissions contributed 5.3 billion tons CO2 eq in 2018, a 14 percent growth since 2000 (FAO, 2018).
This report focuses on one of the prominent greenhouse gases, i.e., methane emission from rice production.
Releasing of one kg of methane into atmosphere is about equivalent to releasing 84 kg of carbon dioxide. Rice
production is estimated to be responsible for 12% of total methane global emissions, mainly due to its anaerobic
decomposition during its production processes (GEF, 2019). In Southeast Asia, one of the world’s major rice
bowls, rice cultivation contributes 25-33% of the methane emission (Umali-Deininger,2022).
Methodology
To estimate the methane emissions from rice production, the tiered methodology provided by IPCC (2006) for
Croplands was used. Flooded rice fields produces methane (CH4) by anaerobic decomposition of organic
material which then escapes to the atmosphere primarily by transport through the rice plants (Takai, 1970;
Cicerone and Shetter, 1981; Conrad, 1989; Nouchi et al., 1990). The annual amount of CH4 emitted from a
given area of rice depends on number and duration of crops grown, water regimes before and during cultivation
period, and organic and inorganic soil amendments (Neue and Sass, 1994; Minami, 1995). Soil type,
temperature, and rice cultivar also affect CH4 emissions.
The basic equation to estimate CH4 emission from rice cultivation is given by equation:
𝐶𝐻4 𝑅𝑖𝑐𝑒 = ∑(𝐸𝐹𝑖,𝑗,𝑘 ∗ 𝑡𝑖,𝑗,𝑘 ∗ 𝐴𝑖,𝑗,𝑘 ∗ 10−6
𝑖,𝑗,𝑘
)
where, CH4rice is the annual methane emissions from rice cultivation in Gg CH4 yr-1
EFijk is the daily emission factor for i, j, and k conditions in kg CH4 ha-1 day-1
tijk is the cultivation period of rice for i, j, and k conditions in day
Aijk is the annual harvested area of rice for i, j, and k conditions in ha yr-1
i, j, and k = represent different ecosystems, water regimes, type and amount of organic amendments, and
other conditions under which CH4 emissions from rice may vary.
It is the product of daily emission factor, cultivation period of rice and annual harvested areas. In the simplest
form, this equation can be implemented using national activity data (i.e., national average cultivation period of
rice and area harvested) and a single emission factor. However, the natural conditions and agricultural
management of rice production varies in different countries. It is therefore necessary to account for the total
harvested area into sub-units under different water regimes multiplied by the respective cultivation period and
emission factor that is representative of the conditions that define the sub-unit. With this disaggregated
approach, total annual emissions are equal to the sum of emissions from each sub-unit of harvested area.
The conditions influencing the CH4 emission from rice cultivation are as follows:
2. 1. Regional differences in rice cropping practices:
Large countries have distinct agricultural regions with distinct climate and production systems which requires
a separate set of calculations for each region.
2. Multiple crops
If rice is harvested more than one time on a given area of land during the year, calculations should be performed
for each season, as the growing conditions vary among cropping seasons.
3. Water regime
Water regime is defined as a combination of:
3.1. Ecosystem type: Separate calculations should be undertaken for each rice ecosystem (i.e., irrigated,
rainfed, and deep-water rice production).
3.2. Flooding pattern: Rice ecosystems can further be distinguished into continuously and
intermittently flooded (irrigated rice), and regular rainfed, drought prone, and deep water (rainfed),
according to the flooding patterns during the cultivation period.
4. Organic amendments to soils
The impact of organic amendments on CH4 emissions depends on type and amount of the applied material.
Organic material incorporated into the soil can either be of endogenous (straw, green manure, etc.) or
exogenous origin (compost, farmyard manure, etc.). Calculations of emissions should consider the effect of
organic amendments.
5. Other conditions:
Factors such as soil type, rice cultivar, sulphate containing amendments can significantly influence CH4
emissions. Inventory agencies are encouraged to make every effort to consider these conditions if country-
specific information about the relationship between these conditions and CH4 emissions is available.
Furthermore, scaling factors are used to adjust the emission factor to account for the conditions mentioned
above. The equation for the adjusted daily emission factor is given by:
𝐸𝐹𝑖 = 𝐸𝐹𝑐 ∗ 𝑆𝐹𝑤 ∗ 𝑆𝐹𝑝 ∗ 𝑆𝐹𝑜 ∗ 𝑆𝐹𝑠,𝑟
Where:
EFi = adjusted daily emission factor for a particular harvested area
EFc = baseline emission factor for continuously flooded fields without organic amendments
SFw = scaling factor to account for the differences in water regime during the cultivation period
SFp = scaling factor to account for the differences in water regime in the pre-season before the cultivation
period
SFo = scaling factor should vary for both type and amount of organic amendment applied
SFs,r = scaling factor for soil type, rice cultivar, etc., if available
The most important scaling factors, namely water regime during and before cultivation period and organic
amendments, are represented in Tables 5.12, 5.13, and 5.14 of the Chapter 5 in IPCC (2006), respectively,
through default values. The values vary with the detail information that can be achieved in each location.
3. Country-specific or location specific scaling factors should only be used if they are based on well-researched
and documented measurement data. It is encouraged to consider soil type, rice cultivar, and other factors if
available.
Table 25 shows the data required for estimating methane emission from rice cultivation.
Table 1: Input data table for estimating methane emission from the rice cultivation
Variable Description Source
Area of the harvested rice Distinct rice polygons (with information on rainfed
or irrigated system if available)
National LULC map
Cultivation period of rice Vary with the cropping season Based on the information
provided by national or local
agricultural statistics or field
surveys, the values for
emission factor can be
obtained from tables in
2006 IPCC Guidelines for
National Greenhouse Gas
Inventories for Croplands
