Soil Fertility & Crop Nutrition 1676 Agronomy Journal  Volume 103, Issue 6  2011 Optimal Nitrogen Fertilization Timing and Rate in Dry-Seeded Rice in Northwest India G. Mahajan, B. S. Chauhan,* and M. S. Gill Published in Agron. J. 103:1676–1682 (2011) Posted online 15 Sep 2011 doi:10.2134/agronj2011.0184 Copyright © 2011 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. R ice production in the northwest part of the IGP is critical for India’s food security as this region contributes more than 50% of the rice procured by the Indian government for bufer and distribution to the public (Dhillon et al., 2010). Te state of Punjab alone contributes 35 to 45% of rice to the national pool despite its small size; it occupies only 1.5% of the geographical area of the country (Hira, 2009). As the epicenter of the Green Revolution of the 1960s and 1970s, Punjab’s agri- cultural fecundity earned the state the recognition as the food bowl of India. Rice in this region is grown using the traditional system of puddling and transplanting, which has led to overuse of water for the last three to four decades. Te underground water level in Punjab has declined by an average of 54 cm yr –1 between 1996 and 2006, with the rate of decline increasing to 1 m yr –1 in many regions in recent years (Hira, 2009; Rodell et al., 2009; Humphreys et al., 2010). In addition to being water- intensive, the puddled-transplanted rice is highly labor-intensive as well. To sustain rice production and productivity over a longer period, alternate rice production systems are required. Due to rapid depletion of underground water and shortage of labor, farmers and scientists in Punjab have initiated experiments with DSR production, though with assured irrigation. Dry-seeded rice is an alternative production system that could help in saving water and labor costs (Pandey and Velasco, 2005; Prasad, 2011). Preliminary extrapolation domain analysis sug- gests that DSR could be adopted on a large area in IGP where the rice–wheat cropping system predominates (Humphreys et al., 2010). Nitrogen is the most important yield-limiting nutri- ent for rice (Fageria et al., 1997). In Punjab, 120 kg N ha –1 , applied at key growth stages, is recommended for transplanted rice (Varinderpal-Singh et al., 2010). Te study of Mahajan and Timsina (2011) in DSR revealed that the crop responds up to 150 kg N ha –1 under weed-free environments; however, under weedy environment, the crop responds only up to 120 kg N ha –1 . In that study, N was applied in four splits and no comparisons were made among diferent split applications. Furthermore, the study pointed to the need to study crop dry matter and N translocation in response to nutrient supply so that optimum N management strategies for enhancing crop production and nutrient-use efciency in DSR can be developed. Since the concept of DSR in northwestern IGP is new, rela- tively few insights into N dynamics and fertilizer N use exist. In puddled soils, ammonium is the dominant form of available N and is lost through ammonia volatilization (Vlek and Craswell, 1981). Some of the ammonia is nitrifed in oxidized soil zones and in foodwater (De Datta, 1981). Tis nitrate moves into reduced layers, where it denitrifes and is subsequently lost to the atmo- sphere as N 2 and N 2 O (De Datta, 1981). Since nitrate is barely present in fooded rice soils, very little nitrate N is leached to the groundwater (Bouman et al., 2002). In aerobic systems, on the ABSTRACT Dry-seeded aerobic rice ( Oryza sativa L.) (DSR) is an emerging production system in the northwest Indo-Gangetic Plains (IGP) due to increasing constraints of labor and water availability. Very limited research has been done in this region on optimizing nutrient management to produce high yield in DSR. In this study, we investigated yield and dry matter of rice, and N transloca- tion in response to timing and rate of N application. Nitrogen was applied in three splits (as per regional recommendation of transplanted rice) and four splits with or without N application at sowing time (basal dose) at rates of 120, 150, and 180 kg ha –1 . Te crop did not respond to increasing N levels from 120 to 180 kg ha –1 when applied in three splits. However, increasing N application to 150 kg ha –1 when applied in four splits with no N at sowing time resulted in 7.55 and 7.76 Mg ha –1 yields in 2009 and 2010, respectively; highest among all the treatments. Application of 150 kg N ha –1 in four splits with no-N at sowing resulted in 9 to 12, 19 to 24, and 5% increase in panicle number m –2 , flled grains panicle –1 , and 1000-grain weight, respectively, over the application of 120 kg N ha –1 in three split doses. Te relative contribution of mean preanthesis assimilates to grain increased from 23% at 120 kg N ha –1 applied in three splits to 40% at 150 kg N ha –1 applied in four splits with no N at sowing, indicating that fertilizer application schedules for transplanted rice are not suitable for DSR. Tis study revealed that application of N at anthesis may further boost the productivity of DSR. From these results, it could also be inferred that, for DSR, application of N at sowing time can be skipped because it may not be immediately used by the emerging seedlings. G. Mahajan and M.S. Gill, Punjab Agricultural Univ., Ludhiana, Punjab, India; B.S. Chauhan, Crop and Environmental Sciences Division, International Rice Research Institute, Los Baños, Laguna, Philippines. Received 12 June 2011. *Corresponding author (b.chauhan@cgiar.org). Abbreviations: DAS, days afer sowing; DSR, dry-seeded aerobic rice; IGP, Indo-Gangetic Plains; LAI, leaf area index; NHI, nitrogen harvest index; RWC, relative water content; 3S+B, three equal nitrogen splits (at sowing, 21 DAS, and 42 DAS); 4S+B, four equal nitrogen splits (at sowing, 21 DAS, 42 DAS, and 63 DAS); 4S-B, four equal nitrogen splits with no nitrogen at sowing (15 DAS, 30 DAS, 45 DAS, and 60 DAS). Published November, 2011