Wetland Rice Cultivation: A Major Cause of Global Warming

Sanjeet

sanjeet.biotech@gmail.com

Emerging Science, 2011, 3(10): 15-18.

Abstract

In this paper, author presented the results of literature on the relation between global warming and wetland rice cultivation, their effect and future plan to reduce methane emission from wetland rice cultivation to protect our climate.

Key  words: Rice cultivation, Methane emission, Modelling of emission, Global warming.

Introduction

Global warming and climate change are one of the most critical global challenges for our country. People concern about global warming mostly focuses on greenhouse gases and methane is the one of major component, which is increasing at the rate of 1 % per year, is likely to contribute more to future climatic change. (Cicerone & Oremland 1998).Wetland rice fields have been identified as a source of atmospheric methane and the emission estimates from paddies range from 29 to 61 Tg per year(IPCC 2002).Rice cultivation is an important agricultural priority worldwide, because rice is the major cereal crop feeding two-third of the global population, which continue to increase by  ̴ 80 million people per year(Cohen 2003), and is expected to continue to feed large numbers of the ever-growing populations(Babu et al., 2005), so it has been estimated that global rice production must almost double by the year 2020 in order to meet the growing demand(Li C et al., 2002), and this may increase methane fluxes by up to 50%(Bouwman 1991).Contribution of methane to the green house effect is ̴ 1.7 wm² and 20% total methane emission comes from paddy field(Purkit et al. 2007).In India measurement of methane emission from rice paddies were initiated by Saha et al., &  Parashar et al., estimated methane emission from India’s paddy at 3 Tg/yr, based on a limited number  of field measurements. Recently, Bhutia et al., used IPCC default flux values for the base year 1994-1995 to estimate methane emissions from all agricultural fields in India to arrive at figure of 2.9 Tg/yr(Babu et al., 2005).According to Purkit et al., 2007 the total harvested rice area of India is nearly 42.23 Mha and total methane emission is nearly 4 Tg per year.

How Methane is Produce in Wetland Rice Cultivation.

In wetland rice cultivation, methane is produced due to the anaerobic decomposition of organic materials in flooded rice paddy soil. Methane is produced as the last step of the anaerobic breakdown of organic matter in wetland rice soils with the help of methanogenic bacteria by transmethylation. The level of methane emission from rice paddy is related to various factors that control the activity of the methenogen and methane-oxidizing bacteria such as temperature, pH, soil redox potential & substrate availability, soil type, rice variety, tillage, water management & fertilization (Conard 2002).Mitra et al., have recently reported that the methane emission is related to also concentration of organic carbon. According to Purkait et al., 2007, methane from paddy field is released into the atmosphere by:-

·        Diffusion from the interfaces following the concentration gradient.

·        Forming gas bubbles and escaping into the atmosphere by ebullition or burst.

·        Diffusion into the root and aerenchyma of the plant. It implies that in addition to the normal process of methane emission.

·        Emission in the form of ebullition occurs during moderate and high emission periods.

Modelling for methane emission

There are many types of models available to predicate the rate of methane emission from wetland rice field. Some models tried to use the least number of input parameters and more empirical equations to capture basic pattern of gas fluxes, these models are :-( Sources –Babu et al., 2005)

·        DNDC

·        Expert-N

·        CASA

·        CENTURY

·        NLOOS

·        MERES

·        MEM

·        DAYCENT

·        INFOCROP.

Among above model the DNDC model was developed for the predication of C and N biogeochemical cycles in both upland and wetland ecosystems (Li et al.,1992, Li et al.,1994 & Babu et al.,2005.).It is powerful assessment tool because it can predict crop grain and shoot yield, gaseous methane, nitrous oxide, ammonia emissions, soil C balance and N leaching below the root zone.  DNDC was also developed for predicting carbon sequestration and trace gas emission for non-flooded agricultural lands, simulating the fundamental process controlling the interaction among ecological drivers, soil environment factors and relevant biochemical or geochemical reactions, which collectively determine the rates of trace gas production and consumption in agricultural ecosystems (Li et al.,1994, Li et al.,1996 & Babu et al.,2005).

                      Using MEM model, Cao et al., estimated methane emission from rice fields in China and Matthews et al. estimated Methane emission from rice fields in China, India, Indonesia, the Philippiness and Thailand( Matthews et al.,2000 ).

Factors for Methane emission

In wetland rice cultivation, there are many factors for appropriate methane emission, which control the activity of the methanogens and methane-oxidizing bacteria, such as temperature, pH, soil redox potential and substrate availability, soil type, water management etc are major. Rice plant influence methane production by enhancing anaerobic conditions due to root respiration, and by provide substrate for methanogens such as root exudates (Neue,1997).  The plant can also affect methane oxidation by enxymatic oxidation and diffusion of oxygen through aerenchyma into the rhizosphere(Epp & Chanton, 1993k ).N fertilization also stimulates the methane oxidizing bacteria(Bodelier et al.,2000).

Table No. : - Values of soil parameters (sources –Purkait et al.,2007).

Parameters	Kharif	Rabi
pH	7.6	7.8
C/N ratio	21.25	10.25
Cation exchange capacity	9.7	5.5
Sand %	12.6	12.8
Clay %	42.6	45.6

Reduction of methane emission

Significant decrease of methane emission from wetland rice field could be achieved using:-

·        Zero tillage and mulching reduce methane emission from wetland rice cultivation.

·        Change of cultivation practices, such as a shift from transplanting to direct seeding and appropriate water management can also contribute water management can also contribute decreasing of methane emissions.

·        Reducing the time during which the fields are flooded, can reduce GHG emissions by about 50 %(Cole et al.,1997).

·        Intermittent drainage is the most effective methane emission mitigation practice for irrigated rice paddies(Majumadar,2003).

·        Improved rice cultivator's have been estimated to reduce GHG emissions by up to 20%(Sass et al. 1992).

·        Fertilization with iron (Conrad 2002),or increased ferric iron content in the rhizosphere seems to suppress methane formation (Watanabe 1999k),

·        Also sulphate inhibits methane production (Denier et al 2001).

·        Rabi cultivation is encouraged to reduce methane emission (Purkait et al., 2007).

Conclusion

Wetland rice cultivation contributes a significant proportion of methane emission, & it is predicated to increase as the global population depends on wetland rice particularly in India and other Asian country. By using different approaches which described above, can reduce the emission of methane and  check the climate change and  global warming due to wetland rice cultivation, also need the global research and policy support.

References:

Cicerone, R. J., and R. S. Oremland. 1988. Biogeochemical aspects of atmospheric methane. Global Biochem. Cycles 2: 299-327.

Denier van der Gon, H.A., van Bodegom, P.M., Wassmann, R., Lantin, R.S. and Metra-Corton, T.M., 2001. Sulfate-containing amendments to reduce methane emissions from rice fi elds: mechanisms, eff ectiveness and costs. Mitigation and Adaptation Strategies for Global Change 6 (1),71-89.

Sass, R.L., Fisher, F.M., Wang, Y.B., Turner, F.T. and Jud, M.F., 1992. Methane emission from rice fi elds: the eff ect of fl oodwater management. Global Biogeochemical Cycles 6, 249–262.

Epp, M. and Chanton, A.J.P., 1993. Rhizospheric methane oxidation determined via the methyl fl uoride inhibition technique. Journal of Geophysical Resources 98, 18422–18423.

IPCC, Special report on Emission Scenarios , Cambridge University Press, Cambridge, UK 2002.

Watanabe, A. and Kimura, M., 1999. Infl uence of chemical properties of soils on methane emission from rice paddies. Communications in Soil Science and Plant Analysis 30, 2449–2463.

Takai, Y. 1970. The mechanism of methane fermentation in flooded soils. Soil Sci. Plant Nutr. 16: 238

Cicerone, R. J., and J. D. Shetter.1981. Sources of atmospheric methane: measurements in rice paddies and a discussion. J. Geophys. Res. 86: 7203-7209.

Conrad, R., 2002. Control of microbial methane production in wetland rice fi elds. Nutrient Cycling in Agroecosystems 64, 59-69.

Cohen, J. E., Human population : The next half century, Science, 2003, 302, 1172-1175.

Y.Jagadeesh Babu, C. Li, S. Frolking, D.R.Nayak, A.Datta and T.K.Adhya, Current Science, Vol.,89. No. 11, 10 December 2005.

Li, C. et al., Reduced methane emissions from large-scale changes in water management in China’s rice paddies during 1980-2000, Geophys. Res. Lett., 2002,29.

Bouwman, A.F., Agronomic aspects of wetland rice cultivation & associated methane emission. Biogeochemistry, 1991, 15. 65-88.

N.N.Purkait, A.K. Saha & Sanghamitra De., Behavior of methane emission from a paddy field of high carbon content. Indian Journal of Radio & Space Physics,  Vol- 36, February 2007, pp- 52-58.

Parashar, D.C. et al., Methane budget from Indian paddy fields. In Methane and Nitrous oxide : Global Emission & Controls from Rice Fields and other Agricultural and Industrial Sources (eds Minami, K., Mosier, A. R. and Sass, R.) NIAES series 2, Tsukuba. Japan, 1994, pp- 27-39.

Mitra  A. P,  Gupta P K & Sharma C, Refinement in methodologies for methane budget estimation from rice paddies, Nut Cycl Agroeco (The Netherlands), 58 , 2002, 201.

Sass R. L., Fischer F.M, Harcombe P.A & Fund M.F., Methane emission from rice fields as influenced by solar radiation, temperature and straw, Global Biogeochem Cycles (Sweden). 5, 1991, 275.

Saha A.K., Rai J. Raman V, Sharma R.C, Parashar D.C, Sen S. P. & Sarkar B, Methane emission from inuandated fields in monsoon region . Indian J. Radio & Space Phys, 18,1989,215.

Matthews, R.B., Wassmann, R. & Arah,J., Using a crop /soil simulation model and GIS techniques to assess methane emissions from rice fields in Asia. I Model development, Nutr. Cycl. Agroecosyst., 2000, 58, 141- 159.

Cao, M., Dent, J.B. & Heal, W.O., Methane emission from China’s rice paddies. Agric. Ecosyst. Environ., 1995. 55, 129-137.

Li, C.S., Frolking, S. & Harriss.R.C., Modeling carbon biogeochemistry in agricultural soils. Global Biogeochem, Cycles, 1994, 8, 237-254.

Li, C., Narayanan, V. & Harriss, R.C., Model estimates of nitrous oxide emission from agricultural lands in the United States.Global Biogeochem Cycles, 1996. 10, 297-306.

Neue, H.U., 1997. Fluxes of methane from rice fi elds and potential for mitigation. Soil Use and Management 13, 258-267.

Bodelier, P.L.E., Hahn, A.P., Arth, I.R. and Frenzel, P., 2000. Eff ects of ammonium-based fertilization on microbial processes involved in methane emission from soils planted with rice. Biogeochemistry 51,225–257.

Cole, C.V., Duxbury, J., Freney, J., Heinemeyer, O., Minami, K., Mosier, A., Paustian, K., Rosenberg, N., Sampson, N., Sauerbeck, D. and Zhao, Q., 1997. Global estimates of potential mitigation of greenhouse gas emissions by agriculture. Nutrient Cycling in Agroecosystems 49, 221–228.

Majumdar, D., 2003. Methane and nitrous oxide emission from irrigated rice fi elds: Proposed mitigation strategies. Current Science 84 (10), 1317-1326

Li,C.S., Frolking,S. & Frolking T.A., A model of nitrus oxide evolution from soil driven by rainfall events. I. model structure and sensitivity, J. Geophys. Res., 1992, 97, 9759-9776.

Sanjeet Kumar

Regional Institute of Education (NCERT)

Bhubaneswar.