Stable isotope evidences for identifying crop water uptake in a typical winter wheat-summer maize rotation field in the North China Plain.

Better managing agricultural water resources, which are increasingly stressed by climate change and anthropogenic activities, is difficult, particularly because of variations in water uptake patterns associated with crop type and growth stage. Thus, the stable isotopes δ18O and δ2H were employed to investigate the water uptake patterns of a summer maize (Zea mays L.) and winter wheat (Triticum aestivum L.) rotation system in the North China Plain. Based on the soil water content, soil layers were divided into four groups (0-20cm, 20-40cm, 40-120cm, and 120-200cm) using a hierarchical cluster analysis. The main soil layer of water uptake for summer maize was from 0-20cm at the trefoil (77.8%) and jointing (48.6%) stages to 20-40cm at the booting (33.6%) and heading (32.6%) stages, became 40-120cm at the silking (32.0%) and milking (36.7%) stages, and then returned to 0-20cm at the mature (35.0%) and harvest (52.4%) stages. Winter wheat most absorbed water from the 0-20cm soil water at the wintering (86.6%), seedling (83.7%), jointing (45.2%), booting (51.4%), heading (28.8%), and mature (67.8%) stages, but it was 20-40cm at the flowering (34.8%) and milking (25.2%) stages. The dry root weight density was positively correlated with the contributions of the water uptake for winter wheat. However, no similar correlation was found in summer maize. Regression analysis indicated that the soil volumetric water content (SVWC) was negatively correlated with the contribution of the water uptake (CWU) for summer maize (CWU=-0.91×SVWC+57.75) and winter wheat (CWU=-2.03×SVWC+92.73). These different responses to water uptake contributions suggested that a traditional irrigation event should be postponed from the booting to flowering stage of winter wheat. This study provides insights into crop water uptake and agricultural water management.