Increasing industrialisation and developmental activities across the globe have led to stress on the Earth’s resources. One of the major damaging impacts of this increasing developmental activity (especially industrial and agricultural) is increasing concentration of the greenhouse gases (GHGs), namely, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), chlorofluorocarbon (CFCs), etcetera, which are potential causes of global warming due to the enhanced greenhouse effect. CO2, CH4 and N2O are key GHGs that contribute toward global warming at 60%, 15% and 5% respectively [1, 2]. Concentrations of these gases in the atmosphere are increasing at 0.4%, 0.3% and 0.22% per year respectively [1, 3]. On average, the agricultural sector emits about 47% and 58% of total global anthropogenic emissions of CH4 and N2O respectively. Although CH4 and N2O emission constitutes only about 20% of the total GHG emissions, they play a significant role in global warming due to their higher values of global warming potential (GWP) of 21 and 310 respectively. It has been estimated that about 74% of the agricultural GHG emissions are from non-annex1 countries . The amount of CH4 emission from paddy fields (about 50 to100 Tg yr-1) accounts for about 10% to 20% of total CH4 emission around the world. Huang et al.  projected that the CH4 emission from rice fields may increase to 145 Tg yr-1 by 2025. Industrial nitrogen fixation for use in agriculture had increased from less than 10 Tg yr-1 in the 1950s to over 80 Tg yr-1 by the year 2000. Nitrogen applied in agricultural systems is emitted in different forms like dinitrogen, ammonium, dissolved organic nitrogen or NOx. Of all these N2O, which is increasing in the atmosphere at the rate 0.2% to 0.3% per year, is of particular concern .
The anthropogenic emission of CO2, CH4 and N2O in India was about 1,398,700 Gg, 20,560 Gg and 240 Gg respectively in the year 2007 . In 2007, the agriculture sector was the largest source of CH4 emission, accounting for about 65% of the total. Of this, livestock, paddy cultivation and onsite burning of crop residues represented shares of 48%, 16% and 1% respectively. In view of this, Indian scientists have placed special emphasis in recent times on the exploration of CH4 emission from paddy fields [8–12]. In 2007, the agricultural sector accounted for about 65% of total N2O emission in India. The main source of direct and indirect N2O emission in agriculture was the application of nitrogen fertilizer2. In 2008, the Government of India (GoI) came up with the National Action Plan on Climate Change. Of the eight national missions mentioned in this plan, one deals with a national mission for sustainable agriculture . After the energy sector, being a dominant and dynamic source of GHG emission, the agricultural sector got special attention for studies and management to abate GHG emissions . It has been easy to change the technology to reduce GHG emission from the energy sector either by using regulatory norms or good backstop technology. However, this is not the case with the agricultural sector, as agriculture directly deals with the cultural, socio-economic matrix of society and farmers, and local setup. So, it is not easy to assess the emissions, due to the random distribution of variables on which emissions depend, or to develop a proper mitigation plan at field level. Few studies have been taken at experimental level to estimate GHG emissions at the local level [15, 16].
National level data provides lots of information and inputs for national and international level planning and negotiation. However, data and information at district level would be imperative and very important in the near future for local level decision-making, and for upcoming district and regional planning activities initiated at local and regional level in the age of the decentralised planning approach. It is unanimously accepted across the scientific and policy-making bodies that while climate change and global warming is a global phenomenon, its solution lies at the level of local planning and adaptation. Considering this background, a local level study was carried out by estimating district-wise emission of CH4 and N2O from rice paddy and agricultural fields respectively for the state of Assam, India, as per the Intergovernmental Panel on Climate Change (IPCC) guidelines and using other available emission factors3. Assam is the gateway to the north-eastern part of India, situated between 90° to 96° longitude east and 24° to 28° latitude north. Assam is bordered in the north and east by the Kingdom of Bhutan and Arunachal Pradesh state. The states, namely, Nagaland, Manipur and Mizoram are situated in the South of Assam, and West Bengal state and Bangladesh to the west. Meghalaya state lies to the south-west of Assam.