Info

36 83a a 60 23

Data from IPCC (2001)

- not estimate, blank: no aim to estimate originally aWaste treatment included under ruminants bRice agriculture included under wetlands

16.3 Rice Paddy as a Source of CH4

Among the basic needs, food is the foremost necessity of human needs. To meet the growing demand of burgeoning human population, the world's annual rice production must increase from the present 520 million tons to at least 880 million tons by 2025, as rice is a staple food for more than half of the world's population (Lampe 1995). Among the biological sources, paddy fields are a major contributor to CH4 emission, accounting for about 15-20% of the global atmospheric CH4. Methan emission from paddy fields of different continents has been reflected in Table 16.2. It is further projected that the CH4 emission from rice cultivation may increase from 1990 level of 97 to 145Tgyr-1 in 2025 (Anastri et al. 1992), as rice is cultivated world wide between 50° N and 35° S and about 90% of the harvested area is located in Asia. Along with CH4, CO2 and N2O are also emitted from the paddy fields. Tsuruta et al. (1998) calculated the contributions of GHGs (CO2, CH4 and N2O) emissions from Japanese paddy fields to the GWPs with a 100-year time horizon and the effluxes of CH4, CO2 and N2O were accounted for 16.0, 78.2 and 5.8 of the total CO2-equivalent emission, respectively. Therefore, a decrease in CH4 emission from paddy fields has far reaching impact on global warming.

Recent studies have estimated CH4 emission from paddy fields at 53 Tg CH4 yr-1 (Chanton et al. 1997), 25-54 Tg CH4 yr-1 (Mosier et al. 1998), 33-49 Tg CH4 yr-1 (Neue and Sass 1998) or 25.1 Tg CH4 yr-1 (Yan et al. 2003), although studies conducted before 1990 had given higher estimates (Holzapfel-Pschorn and Seiler 1986; Aselman and Crutzen 1989). The methane budget from Indian paddies has been estimated to be an average of 4.3 Tg Yr-1 with a range between 2.7 and 5.4 Tg Yr-1 in Methane Campaign 1991 (Parashar et al. 1997).

Later on, Methane Asia Campaign (MAC) (1998) computed a CH4 budget for Indian paddy fields to be 3.61 Tg/yr as depicted in Table 16.3. The recent estimates of paddy emissions account for 4.2-9.0% of the total global CH4 emission (600 Tg CH4 yr-1) (Minamikawa et al. 2006). Before that, Kumaraswamy et al. (2000) reviewed CH4 emission from paddy fields, while Le Mer and Roger (2001) estimated CH4 production, oxidation, emission and consumption separately in various paddy soils.

Table 16.2 Methane emission from paddy fields of different continents

Ecosystem

Location

Total emission (Tg yr 1)

Total emissions

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