Madras Agric. J., 104 (10-12): 335-339, December 2017 *Corresponding author’s email: parameswariphd@gmail.com Infuence of Nitrifcation Inhibitor on Green House Gas (GHG) Emission under Intensive Paddy System E. Parameswari*, V. Davamani, S. Arulmani and V.Ravi Horticultural College and Research Institute Tamil Nadu Agricultural University Periyakulam - 625 604 The feld experiments were carried out to assess the infuence of Dicyandiamide (DCD) along with nine diferent nitrogen management practices on emission of methane (CH 4 ) and nitrous oxide (N 2 O) under intensive paddy system of Cauvery Delta Zone. The CH 4 and N 2 O efux clearly showed daily and seasonal fuctuations. Among the treatments, Leaf Colour Chart (LCC) based N (30 kg N ha -1 keeping the LCC value 4 as standard + DCD @ 10 % of applied N) recorded the lowest average emission of 0.50 mg.m 2 .day -1 and 2.93 mg.m 2 .day -1 of N 2 O and CH 4 , respectively. Irrespective of all treatments, among the critical stages of crop growth, fowering stage recorded highest emission of 23 % N 2 Oand 50 % of CH 4 when compared to tillering stage. Among the “N” applied treatments, Leaf Colour Chart (LCC) based N + DCD recorded the lowest seasonal green house gas emission (0.49 kg ha -1 & 0.44 kg ha -1 of N 2 O and 2.94 kg ha -1 & 3.20 kg ha -1 of CH 4 during Kharif and Rabi seasons, respectively) along with higher paddy yield (12 to 15%). Key words: Dicyandiamide, Nitrogen fertilizer, Nitrous oxide, Methane, Paddy Methane and nitrous oxide are the two major Green House Gases (GHG) emitted from paddy (Oryza sativa L.) agro-ecosystem. At global level, rice cultivation alone contributes 10 % of the total CH 4 emission while the global warming potential of N 2 O is 298 times higher (Rees et al. 2013) than carbon di-oxide, so mitigation of both CH 4 and N 2 O is needed to combat global warming. In fooded rice, methanogens bacteria consume soil organic carbon and emit CH 4 . In rice soil, N 2 O is produced by both biological (nitrifcation and denitrifcation) and chemical decomposition process. Nitrogen based fertilizer is main source of N 2 O production in rice soil. Methane and N 2 O production in rice soil is infuenced by several factors such as water, soil pH, redox potential, temperature, organic matter of soil, soil microbial diversity, transplanting methods, rice cultivar, crop duration and type & time of fertilizer application (Hussain et al., 2015). Application of “N” fertilizers increases N 2 O emissions (Bronson and Mosier, 1992). Emissions of N 2 O from N-fertilized croplands vary considerably, ranging between 0.001% and 6.8% of applied “N” (Bouwman, 1990; Eichner, 1990). From the agricultural soils, nitrifcation and denitrifcation are the two processes responsible for formation of N 2 O. In both these processes, nitrite (NO 2 - ) is formed as an intermediate compound. During the process of nitrifcation, NH 4 + , in aerobic condition, gets oxidized to NO 3 - via hydroxylamine and nitrite, releasing N 2 O as a byproduct, while in denitrifcation, the NO 3 - gets completely reduced to N 2 evolving N 2 O as an intermediate product. Therefore, the end product of nitrifcation works as substrate for denitrifcation. Hence, controlling the frst process will certainly help in regulation of second process to ome extent. Nitrifcation inhibitors are compounds that reduce the rate at which ammonium is converted to nitrate either by killing or interfering with the metabolism of nitrifying bacteria. Dicyandiamide (DCD) is one of the most widely used bacterio-static nitrifcation inhibitors in the agriculture (Zacherl and Amberger, 1990) and decomposes in soil to non-toxic products. Efect of DCD on N 2 O emissions has been reported by Mosier et al. (1996) in wheat and maize and McTaggart et al. (1997) in ryegrass, grassland and spring barley. The present study was undertaken to observe the efect of DCD on N 2 O & CH 4 efux from irrigated rice soils of Cauvery Delta Zone to assess its suitability for decreasing GHG emission to the atmosphere. Material and Methods The present investigation was carried out during the year 2013-2014 to assess the infuence of Dicyandiamide (DCD) along with nitrogen management practices on the emission of N 2 O & CH 4 from agricultural soils. A feld experiment was conducted at Tamil Nadu Rice Research Institute, Aduthurai (11 0 N latitude, 79 0 31’ E longitude, 19.4 MSL). During normal years, the annual rainfall is 1200 mm of which around 70 % is received during September to October (North East Monsoon). The climate of the experimental site (Cauvery Delta) is sub tropical monsoon type. The experiment with fxed plots has been laid out in a Randomized Block Design (RBD) with three replications. The details of the treatments are listed below.