SI S In - Season Optical Sensing Improves Nitrogen - Use Effi ciency for Winter Wheat

SSSAJ: Volume 73: Number 5 • September–October 2009 Soil Sci. Soc. Am. J. 73:1566-1574 doi:10.2136/sssaj2008.0150 Received 30 Apr. 2008. *Corresponding author ([email protected]). © Soil Science Society of America 677 S. Segoe Rd. Madison WI 53711 USA 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. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. C is the world’s largest producer and consumer of commercial N fertilizers (Smil, 2002), accounting for about 30% of the world total (Zhu and Chen, 2002). Excessive N application to crops raises the potential risk for loading reactive N into the environment and incurs unnecessary additional expense for producers. Th is is particularly the case within intensive agricultural regions of the NCP, where unjustifi ed N-fertilization and irrigation have resulted in signifi cant N leaching or denitrifi cation during the winter wheat growing season (Chen et al., 2005; Li et al., 2007). Th e grain yield per unit applied N in the NCP decreased from 46 kg grain kg−1 N at an application rate of 174 kg N ha−1 yr−1 in 1978 to 21 kg grain kg−1 N at an application rate of 592 kg N ha−1 yr−1 in 1998 (Fang et al., 2006). Nitrogen contamination of water bodies has become an environmental and social issue threatening crop production and human health (Zhang et al., 1996; Liu et al., 2005). Technologies and methods for eff ective N fertilizer management are urgently needed in this area. To advance crop N management in this region, Chen et al. (2006) developed an improved soil test-based in-season N management strategy that credits soil residual mineral N (Nmin) to reduce N application rates without decreasing grain yield. Th is strategy has been evaluated for winter wheat in the NCP over 121 site-years using on-farm experiments. Using the Nmin strategy, an average of 196 kg N ha−1 was saved without any signifi cant wheat grain yield reduction as compared with the typical farmer’s fertilization practice (Cui et al., 2008). However, it is not practical to apply this soil test-based management strategy to large areas for in-season sitespecifi c N management due to labor, time, and expense limitations. F. Li College of Resources & Environ. Sciences, China Agricultural Univerisity 100094, Beijing, China and College of Ecology & Environmental Science Inner Mongolia Agricultural University 010019, Hohhot, Inner Mongolia, China