Effects of winter wheat row spacing on evapotranpsiration, grain yield and water use efﬁciency Suyin Chen a , Xiying Zhang a, *, Hongyong Sun a , Tusheng Ren b , Yanmei Wang a a Key Laboratory of Agricultural Water Resources, Center for Agricultural Resources Research, Institute of Genetic and Developmental Biology, The Chinese Academy of Sciences, 286 Huaizhong Road, Shijiazhuang 050021, Hebei, China b Department of Soil and Water Sciences, China Agricultural University, Beijing 100094, China 1. Introduction The winter wheat and summer corn double cropping system comprises 60% of farmland in the North China Plain (NCP), where 19% of China’s grain is produced. In winter wheat growing season (from October to next June), the precipitation is around 60– 150 mm (Zhang et al., 2003) and evapotranspiration (ET) is about 450 mm (Liu et al., 2002). As a result, irrigation is essential to maintain high winter wheat yields. Because groundwater is the major source of irrigation water, a rapid decline in the ground- water level has been recorded (Zhang et al., 2005). Over the past 20 years, the regional groundwater table has been declining at the rate of over 1 m year 1 . The key to sustainable agriculture in the NCP is to develop techniques that reduce irrigation water use by increasing crop water use efﬁciency (WUE). Evapoatrasiration (ET) consists of crop transpiration (T) and soil evaporation (E). While E may indirectly beneﬁt crop growth, numerous studies have reported that reducing E is an effective measure to conserve soil moisture and improve crop WUE (Melloulo et al., 2000; Kang et al., 2002; Zhang et al., 2005). Many techniques, such as mulching with different materials (e.g., straw, sand, gravel, and plastic ﬁlm), conservation tillage and crop management, have been applied to reduced E (Modaihsh et al., 1985; Urger et al., 1991; Hares and Noval, 1992; Chen et al., 2007). For wheat crops, French and Schultz (1984a,b) suggested an average E value of about 110 mm, in line with other ﬁndings in the literature (from 76 to 120 mm, or 20–77% of the total crop water use) (Eberbach and Pala, 2005). The ratio of E over ET was largely affected by leaf area index (LAI) or canopy coverage and surface soil moisture (Liu et al., 2002), and therefore varies throughout crop growing season. At earlier crop growth stages, LAI is usually small and E is the main component of ﬁeld water use. With increasing canopy size, E becomes less important and T increases signiﬁcantly (Eastham et al., 1999; Copper and Gregory, 1987; Liu et al., 2002). To reduce E, some have suggested increasing the canopy coverage at earlier growth stages by increasing crop density (Lascano et al., 1994), while others proposed to change row spacing and row direction (Lehrsch et al., 1994; Giayetto et al., 2005). Lehrsch et al. (1994) found canopies closed about 20 days earlier with narrow row spacing than with wide row spacing. The fully canopies protected and shaded the soil surface, and reduced water losses by evaporation, and increased water use efﬁciency. Eberbach and Pala (2005) found the architecture of winter wheat canopy affected solar radiation penetration such that under a large row spacing (30 cm), more incident radiation was intercepted at the soil surface. As a result, E of Agricultural Water Management 97 (2010) 1126–1132 ARTICLE INFO Article history: Available online 7 October 2009 Keywords: Winter wheat Soil evaporation Row spacing Grain yield Water use efﬁciency ABSTRACT A ﬁeld study was conducted from 2002 to 2007 to investigate the inﬂuence of row spacing of winter wheat (Triticum aestivum L.) on soil evaporation (E), evapotranspiration (ET), grain production and water use efﬁciency (WUE) in the North China Plain. The experiment had four row spacing treatments, 7.5 cm, 15 cm, 22.5 cm, and 30 cm, with plots randomly arranged in four replicates. Soil E was measured by micro-lysimeters in three seasons and ET was calculated from measurements of soil proﬁle water depletion, irrigation, and rainfall. The results showed that E increased with row spacing. Compared with the 30-cm row spacing (average E = 112 mm), the reduction in seasonal E averaged 9 mm, 25 mm, and 26 mm for 22.5 cm, 15 cm, and 7.5 cm row spacings, respectively. Crop transpiration (T) increased as row spacing decreased. The seasonal rainfall interception and seasonal ET were relatively unchanged among the treatments. In three out of ﬁve seasons, the four different treatments showed similar grain yield, yield components and WUE. We conclude that for winter wheat production in the North China Plain, narrow row spacing reduced soil evaporation, but had minor improvements on grain production and WUE under irrigated conditions with adequate nutrient levels. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +86 311 85871762; fax: +86 311 85815093. E-mail addresses: xyzhang@sjziam.ac.cn, xyzhang@ms.sjziam.ac.cn (X. Zhang). Contents lists available at ScienceDirect Agricultural Water Management journal homepage: www.elsevier.com/locate/agwat 0378-3774/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2009.09.005