Water use and crop coefficient of the wheat–maize strip intercropping system for an arid region in northwestern China

•Wheat–maize strip intercropping system showed the greatest land use efficiency while the sole-cropped maize showed the greatest economic profit.•Wheat–maize strip intercropping system used more water than sole crops.•Wheat–maize strip intercropping system used water as efficiently as sole crops.•Wheat–maize strip intercropping system consumed more water through soil evaporation.•Crop coefficient of the wheat–maize strip intercropping system was investigated. Relay strip intercropping of spring wheat and maize is practiced on a large scale in arid regions of northwestern China. In this study, a field experiment was carried out during 2012 and 2013 growing seasons to examine water use and crop coefficient of this system in an arid environment. The experiment comprised three treatments: sole-cropped wheat, sole-cropped maize, and wheat–maize intercropping. The grain yields of both intercropped wheat and maize were enhanced by intercropping. The gross economic profit for wheat–maize intercropping was 16.4% lower than that of sole maize and 95.4% higher than that of sole wheat. The overall land use efficiency was improved by intercropping. The time course of leaf area index in intercropping had the similar trends to those in sole crops with relatively low values, which never exceeded 3.0m2m−2 throughout both growing seasons. Compared to weighted means of the sole-cropping systems, wheat–maize intercropping used 26% and 24% more water in 2012 and 2013, respectively. The water-use efficiency of intercropping was nearly the same as the weighted means of the sole crops. Due to the incomplete groundcover in intercropping plots, more water was consumed as soil evaporation. Averaged over two seasons, the ratio of soil evaporation to actual evapotranspiration was 33.4, 20.7 and 24.1% for intercropping system, sole-cropped wheat and sole-cropped maize, respectively. Crop coefficient (Kc) of sole-cropped wheat was 0.19±0.02, 1.05±0.07, and 0.42±0.09 at the initial, mid and late season in two seasons, respectively. Kc value of the sole-cropped maize was 0.22±0.03, 1.10±0.06 and 0.60±0.02 at the initial, mid and late season, respectively. The Kc values of the wheat–maize intercropping system varied in 0.21±0.03, 0.89±0.05, and 0.78±0.06 at the initial, middle and late wheat growing season, and in 0.85±0.03 and 0.61±0.01 at the middle and late maize growing season, respectively. Therefore, longer growing season and incomplete ground cover are the main factors that resulted