Mitigation of N2O emission from an alluvial soil by application of karanjin

An incubation experiment was conducted to study N2O emissions from a Typic Ustochrept, alluvial soil, fertilized with urea and urea combined with diff erent levels of two nitrification inhibitors, viz karanjin and dicyandiamid e (DCD). Karanjin [a furano-flavonoid, obtained from karanja (Pongamia glab ra Vent.) seeds] and DCD were incorporated at rates of 5, 10, 15, 20 and 25 % of applied urea-N (100 mg kg(-1) soil), to the soil adjusted to field cap acity moisture content. The highest N2O flux (366 mug N2O-N kg(-1) soil day (-1)) was obtained on day 1 after incubation from soil fertilized with urea without any inhibitor. The presence of the inhibitors appreciably reduced the mean N2O flux from the urea-treated soils. The application of karanjin resulted in a higher mitigation of total N2O-N emission (92-96%) compared t o DCD (60-71%). Rates of N2O flux ranged from 0.9 to 140 mug N2O-N kg(-1) s oil day(-1) from urea combined with different levels of the two inhibitors (coefficient of variation=24-272%). Karanjin (62-75%) was also more effecti ve than DCD (9-42%) in inhibiting nitrification during the 30-day incubatio n period.