Greenhouse Gases from Crop Fields

Zhengqin Xiong and M.A.K. Khalil

6.1 Introduction

A rapid increase in atmospheric concentrations of the three main anthropogenic greenhouse gases (GHGs), like carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), is evident from measurements taken over the past few decades as well as ice-core records spanning many thousands of years (IPCC 2007). The global increases in CO2 concentration are due to fossil fuel and land-use change, while those of CH4 and N2O are primarily from agriculture (Cole et al. 1997; IPCC 2007). Despite large annual exchanges of CO2 between the atmosphere and agricultural lands, the net flux is approximately balanced (IPCC 2007). Arable and permanent crops occupy 1,540 Mha in 2003 which is about 12% of the Earth's land surface (FAOSTAT 2006). In 2005, agriculture contributes about 47 and 58% of total anthropogenic emissions of CH4 and N2O, respectively, with a wide range of uncertainty in the estimates of both the agricultural contribution and the anthropogenic total.

If demands for food increase and diets shift as projected, then annual emissions of GHGs from agriculture may increase proportionately. But improved management practices and emerging technologies may permit a reduction in emissions per unit of food produced, and a reduction in emissions per capita food consumption. We will focus on the processes as sources of CH4 and N2O in crop fields, and on agricultural practices that can influence their emissions.

CH4 is an important greenhouse gas with a global warming potential of about 20 over a 100 year period and it accounts for 20% of the total radiative forcing from all of the long-lived and globally mixed greenhouse gases over the last 100 years. The

College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing, 210095, China e-mail: [email protected]; [email protected]

S.N. Singh (ed.), Climate Change and Crops, Environmental Science and Engineering, DOI 10.1007/978-3-540-88246-6.6, © Springer-Verlag Berlin Heidelberg 2009

Table 6.1 Sources, sinks and atmospheric budgets of CH4 (Tg CH4 year ')

References

Indicative 13C, permil3

Khalil and Shearer (1993)

Mikaloff Fletcher et al. (2004)b

Chen and Prinn (2006)b

IPCC (2007)

Natural sources

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