Abstract: Crop yield and water use efficiency (WUE) in a wheat-maize double cropping system are influenced by short and uneven rainfalls in the North China Plain (NCP). A 2-year experiment was conducted to investigate the effects of irrigation on soil water balance, crop yield and WUE to improve irrigation use efficiency in the cropping system. Soil water depletion (ΔSWS) by crop generally decreased with the increase of irrigation and rainfall, while ΔSWS for the whole rotation was relatively stable among these irrigation treatments. High irrigations in wheat season increased initial soil moisture and ΔSWS for subsequent maize especially in the drought season. Initial soil water influenced mainly by the irrigation and rainfall in the previous crop season, is essential to high yield in such cropping systems. Grain yield decreased prior to evapotranspiration (ET) when ET reached about 300 mm for wheat, while maize showed various WUEs with similar seasonal ET. For whole rotation, WUE declined when ET exceeded about 650 mm. These results indicate great potential for improving irrigation use efficiency in such wheat-maize cropping system in the NCP. Based on the present results, reasonable irrigation schedules according to different annual rainfall conditions are presented for such a cropping system.

Key words: cropping system, crop yield, irrigation schedule, North China Plain, soil water balance, water use efficiency.