Saturday, 15 July 2006

Effect of Microbial Inhibitors on Nitrous Oxide Flux from Paddy Field.

Aditi Srivastava, G.B.Pant Univ of Agriculture and Technology, Dept of Agrometeorology, College of Agriculture, Pantnagar, 263 145, India and Venkatesh Bharadwaj, Dept of Agrometeorology, College of Agriculture, G.B. Pant Univ of Agriculture and Technology, Pantnagar, 263 145, India.

The problems of increasing concentration of green house gases in the atmosphere are being experienced. Global warming of the earth is taking place at an unprecedented rate and climates all over the world are changing rapidly. This unusually high rate of change has been attributed to human intervention into the processes of nature. Nitrous Oxide (N2O) concentration in the atmosphere at present stands at 311 ppbv and is increasing at the rate of 0.25% per year. The effect of Nitrous Oxide on global warming has been reported to be almost 5 % of the total green house gases. Both unfertilized and fertilized soils have been found to be emitting N2O, which is produced during denitrification and nitrification reactions taking place by the soil microbes. The present study was carried out at Crop Research Center of G.B. Pant University of Agriculture and Technology, Pantnagar during the rainy season of 2004 on a silty clay loam soil the objectives of this study were the estimation of N2O flux from paddy fields under the treatment of microbial inhibitors and to find out effective microbial inhibitor in mitigating N2O emission as well as to obtain a profitable yield of the paddy. The rice crop was grown with recommended package of practices with the continuous submergence from transplanting to ripening stage. The nitrous oxide gas was collected by closed chamber technique and its amounts were measured by a gas chromatograph with electron capture detector (ECD) and Porapak N stainless steel column. The temperature for column, injector and detector were 45, 120 and 3000C, respectively. Effects of these treatments were observed upon N2O emission as well as upon the plant growth parameters, yield attributes and yield of paddy. The nine treatments were T1, Control, T2, 100% NPK + Nitrapyrine, T3, 100 % NPK + Nitrapyrine + Green Manure (GM), T4, 100 % NPK + Encapsulated Calcium Carbide (ECC), T5, 100 % NPK + ECC + GM, T6, 100 % NPK + Thiourea (TU), T7, 100 % NPK+ TU+ GM, T8, 100 % NPK + Dicynadiamide (DCD) and T9, 100 % NPK + DCD + GM which emitted an average N2O flux rate of 0.21, 0.44, 0.39, 0.01, 0.43, 0.57, 0.38, 0.28 and 0.25 mg m-2 hr-1. The effect of these treatments on N2O flux was also studied at different growth stage of rice and it was found that at tillering stage the fluxes were in the order of T3 > T6> T9 > T7> T5 > T1 > T8 > T2 > T4 emitting 0.74, 0.70, 0.49, 0.44, 0.27, 0.05, -0.15, -0.27 and -0.51 mg m-2 hr1. At panicle initiation stage average N2O fluxes from different treatments were found to be taking place in the order of T2 > T7> T5 > T8> T9 > T3 > T6 > T1 emitting 2.24, 0.72, 0.70, 0.66, 0.62, 0.51, 0.49, and 0.33 mg m-2 hr1. No particular trend of N2O was observed at reproduction stage corresponding to average fluxes generated at panicle initiation stage. At ripening stage, N2O emission from different treatments took place in the order of T7 > T4> T5 > T6> T8 > T1 > T2 > T3 > T9 emitting 1.03, 0.38, 0.35, 0.11, 0.06, 0.01, -0.003, -0.22 and -0.36 mg m-2 hr1. At maturity stage, N2O fluxes were found in the order of T6 > T8> T3 > T9> T5 > T4 > T1 > T2 > T7 emitting 0.85, 0.57, 0.47, 0.27, 0.23, 0.10, 0.08, -0.08 and 0.21 mg m-2 hr1. Maximum inhibition of N2O emission was observed by 100% NPK + ECC treatment, but this treatment had adverse effect on plant growth as well as yield. The treatment, 100 % NPK + Thiourea + GM had an extremely positive effect on plant growth as well as yield but its inhibitory effect on N2O emission was not found to be substantial in comparison to other treatments. However, the treatment 100 % NPK + Dicynadiamide (DCD) + Green Manure (GM) was found to fit both the roles perfectly. It was able to effectively control N2O emission rate from the soil while also maintaining the yield at a considerably higher level than other treatments.

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