Crop yield and soil nitrogen dynamics in an intermittently flooded rice field affected by nitrification inhibitors (Einfluss von Nitrifikationshemmern auf Getreideertrag und Stickstoffdynamik im Boden in einem zeitweilig u ¨ berfluteten Reisfeld) DEEPANJAN MAJUMDAR Department of Environmental Science, Institute of Science and Technology for Advanced Studies and Research, Gujarat, India (Received 29 November 2004; accepted 1 June 2005) Abstract A field experiment was conducted to study yield and soil N dynamics in an irrigated, intermittently submerged rice field at New Delhi, India, where chemically synthesized as well as neem derived urea coating nitrification inhibitors with prilled urea were applied. Rice (var. IR-32) was grown on a Typic Ustochrept alluvial soil. No nitrogen (control), prilled urea alone, prilled urea mixed with dicyandiamide (DCD), neem (powdered Azadirachta indica Juss. seeds) coated urea and Nimin (commercial derivative of neem) coated urea were tested for their efficacy in regulating yield and conservation of N. None of the inhibitors could increase biomass or grain yield over urea. But all the inhibitors were able to conserve soil ammonium and DCD was the most efficient nitrification inhibitor followed by Nimin coated urea. N- uptake, recovery, physiological and agronomic efficiencies were highest in urea treated plots. The performances of all the inhibitors were against the popular trend where crop yield and N-uptake were enhanced by their application. But, more studies are required on the performance of these inhibitors in rice fields to come to a stronger conclusion. Keywords: Dicyandiamide, neem coated urea, nimin coated urea; IR-32, India Introduction Fertilizer N-use efficiency in flooded rice is low due to various pathways of N-loss like leaching, volatilization, run-off and denitrification (DeDatta 1995). Extensive efforts have been made in the last few decades all over the world to increase fertilizer N-use efficiency in rice (Vlek & Craswell 1979; Vlek et al. 1980; Ghosh et al. 2003). One of the significant strategies to increase N-use efficiency is to use nitrification inhibitors to minimize nitrification Correspondence: Dr Deepanjan Majumdar, Department of Environmental Science, Institute of Science and Technology for Advanced Studies and Research, V.V. Nagar, Gujarat-388120, India. Tel: 02692 234955. Fax: 02692 238355. E-mail: joy_ensc@yahoo.com or joy_ensc@rediffmail.com Archives of Agronomy and Soil Science December 2005; 51(6): 645 – 653 ISSN 0365-0340 print/ISSN 1476-3567 online Ó 2005 Taylor & Francis DOI: 10.1080/03650340500201691