Simulating water use and N response of winter wheat in the irrigated floodplains of Northwest Uzbekistan Yulduz Djumaniyazova a, *, Rolf Sommer b,1 , Nazar Ibragimov a , Jumanazar Ruzimov a , John Lamers c,2 , Paul Vlek c,2 a ZEF – UNESCO Project, Urgench State University, 14 Alimjan St, Urgench 220100, Khorezm, Uzbekistan b International Center for Agricultural Research in the Dry Areas (ICARDA), PO Box 5466, Aleppo, Syrian Arab Republic c ZEF, Center for Development Research, Department of Ecology and Resource Management, University of Bonn, Walter-Flex-Str. 3, 53113 Bonn, Germany 1. Introduction Winter wheat (Triticum aestivum L.) has made a significant contribution to the increase in global food production during the past four decades. Total wheat production rose steadily during this period owing to higher yielding, more water and fertilizer responsive, and more disease resistant cultivars whilst the production was supported by adequate input delivery systems, up-to-date management practices and a strong improvement of the marketing chains (Braun et al., 1998; Dixon et al., 2006). Of the 607 million ton of wheat produced in 2007 worldwide, 308 mil- lion ton originated from developing countries covering 116 mil- lion ha (FAOSTAT, 2007). Since wheat has become one of the most important staples in the world, a wealth of research findings are available on fertilization (e.g., Bole and Dubetz, 1986; Stafford, 1996; Strong et al., 1992; Fowler, 2002), irrigation (e.g., Wright, 1981), crop management (e.g., Engel et al., 1999; Sayre, 2000), breeding (e.g., Stapper and Fischer, 1990; Rawson and Gomez- Macpherson, 2000; Reynolds et al., 2001), grain quality (e.g. Goos et al., 1982; Engel et al., 1997; Carr et al., 2008), and environmental effects (e.g., Wolf et al., 1996; Olesen et al., 2000; Snape et al., 2006). Despite this ample knowledge, little has been documented about irrigated winter wheat in the central Asian country of Uzbekistan, where it was introduced after independence in 1991. By promoting winter wheat, Uzbekistan aimed at self- sufficiency in grain production and a decrease in the prior long- lasting dependency on foreign wheat imports (Eshmirzaev and Yusupov, 1994). Agricultural production in Uzbekistan, including Field Crops Research 116 (2010) 239–251 ARTICLE INFO Article history: Received 31 October 2009 Received in revised form 5 January 2010 Accepted 8 January 2010 Keywords: CropSyst Crop water demand Deficit irrigation Khorezm Aral Sea Basin ABSTRACT The crop-soil simulation model CropSyst was used to simulate growth, water- and N-uptakes of irrigated winter wheat (Triticum aestivum L. cv. Kupava) in Khorezm, in the dry lands of northwest Uzbekistan, Central Asia. CropSyst was calibrated using the findings of field experiments of 2005/06 and 2006/07 and validated for the 2007/08 season. A relative root mean squared error of 11% proved the accuracy between simulated and observed aboveground biomass and grain yield in 2007/08. Scenario analyses showed that N-leaching was high and ranged from 63 to 106 kg ha 1 when irrigated between 749 and 869 mm during the first two cropping seasons. The simulated N-leaching was lowest and ranged from 7 to 15 kg ha 1 when irrigation was only 148–395 mm during 2007/08. The considerable N losses during leaching and high N-uptakes by wheat together resulted in a negative N-balance even during applications of 180 and 240 kg ha 1 of N-fertilizer. N scarcity in the N-balance was reduced with increasing N-fertilizer amounts and ranged from 29 to 153 kg N ha 1 in 2005/06 and 2006/07. Despite a common shallow groundwater table in the region during some time of the year, scenario analysis revealed that only full irrigation water (580 mm) and N supply according to crop demand (180 kg ha 1 ) guaranteed high grain yields, unless the water table is permanently shallow to overcome irrigation deficits. Limited irrigation and N application (40% and 55% of ‘optimal’, respectively) in combination with a groundwater table below 3 m resulted in a 55% yield decline. The CropSyst wheat model proved a robust tool for assessing the influence of water and N dynamics under conditions of varying irrigation and shallow groundwater tables. It thus has potential as a decision support not only in northwest Uzbekistan, but also in comparable regions of Central Asia. ß 2010 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +998 62 2243347; fax: +998 62 2243347. E-mail addresses: yulduz@zef.uzpak.uz, yulduz.d@gmail.com (Y. Djumaniyazova), r.sommer@cgiar.org (R. Sommer), nazar@zef.uzpak.uz (N. Ibragimov), jumanazar@zef.uzpak.uz (J. Ruzimov), j.lamers@zef.uzpak.uz (J. Lamers), p.vlek@uni-bonn.de (P. Vlek). 1 Tel.: +963 21 2691 2590. 2 Tel.: +49 228 731726; fax: +49 228 731726. Contents lists available at ScienceDirect Field Crops Research journal homepage: www.elsevier.com/locate/fcr 0378-4290/$ – see front matter ß 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2010.01.001