Potential use of karanjin (3-methoxy furano-2′,3′,7,8-flavone) as a nitrification inhibitor in different soil types

Karanjin, a furanoflavonoid (3-methoxy furano - 2 ′ , 3 ′ , 7, 8-flavone), is obtained from the seeds of karanja tree (Pongamia glabra Vent.), which is reported to have nitrification inhibitory properties but has been tested in few soil types. Efficiency of karanjin as a nitrification inhibitor in seven different soils of India was tested in a laboratory incubation study. The soils (800 g) were adjusted to field capacity moisture content, fertilized with urea and urea combined with karanjin at a rate of 20% of applied urea-N (100 mg kg ^− 1 soil) and incubated at 35°C for a period of 7 weeks, during which urea [CO(NH₂)₂], ammonium (NH₄  ⁺ ), nitrite (NO₂  ⁻ ) and nitrate (NO₃  ⁻ ) content in the soils was measured periodically and nitrification inhibition at different stages was calculated. Urea hydrolysis was almost complete within 72 h of application in all the soils and was not affected by karanjin. Karanjin had conserved ammonium in all the soils at all stages and nitrate formation was effectively minimized. Nitrite in soils was short-lived and low. Nitrification inhibition by karanjin remained high for a period of approximately 6 weeks, decreased with time and ranged from 9 - 76% for all the soils. The study shows that this plant product can be an effective nitrification inhibitor in several types of soil.