Nitrous oxide (N2O) accounts for 5% of the total enhanced greenhouse effect and responsible for the destruction of the stratospheric ozone. The rice-wheat cropping system occupying 26 million ha of productive land in Asia could be a major source of N2O as most of the fertilizer N in this region is consumed by this system. Emission of N2O as influenced by application of urea, urea plus farm yard manure (FYM), and urea plus dicyandiamide (DCD), a nitrification inhibitor, was studied in rice-wheat systems of Indo-Gangetic plains of India. Total emission of N2O-N from the rice-wheat systems varied between 654 g ha(-1) in unfertilized plots and 1,570 g ha(-1) in urea fertilized plots. Application of FYM and DCD reduced emission of N2O-N in rice. The magnitude of reduction was higher with DCD. In wheat also N2O-N emission was reduced by DCD. FYM applied in rice had no residual effect on N2O-N emission in wheat. In rice intermittent wetting and drying condition of soil resulted in higher N2O-N emission than that of saturated soil condition. Treatments with 5 irrigations gave higher emissions in wheat than those with 3 irrigations. In rice-wheat system, typical of a farmer's field in Indo-Gangetic plains, where 240 kg N is generally applied through urea, N2O-N emission is 1,570 g ha(-1) (0.38% of applied N) and application of FYM and DCD reduced it to 1,415 and 1,096 g ha(-1), respectively.