Continuous regulated deficit irrigation enhances peanut water use efficiency and drought resistance

Regulated deficit irrigation (RDI) is an important means by which the water use efficiency (WUE) of peanut can be improved and facilitates the sustainable development of the peanut industry. However, most studies of RDI have only focused on single growth periods, which limits the water-saving potential. In this study, continuous regulated deficit irrigation (CRDI) was used to significantly improve the WUE of peanut through an experiment employing a split-plot design. Three levels of water deficit treatment, severe (H1/J1, 45% field capacity), moderate (H2/J2, 55% field capacity), and mild (H3/J3, 65% field capacity), were applied in the flower pegging stage (H) and the pod setting stage (J). Moderate CRDI (H2J2) stably improved the instantaneous water use efficiency of peanut leaves. Yield was not significantly decreased under the H2J2 treatment, and was only 4.47% lower than that of the H3J2 treatment, in which the yield was the highest. The highest WUE was observed in the H2J2 treatment (1.87 kg·m−3). The first time that the soil water content reached the lower limit in the pod setting stage, the proline content in the H1J1 treatment was 13.57 times higher than that in the H3J3, indicating that peanuts in the H1J1 treatment experienced substantial drought stress. The second time that the lower limit of soil water content was reached, the proline content in the H1J1 treatment was 7.14 times higher than that in the H3J3 treatment, indicating that the peanut drought resistance was improved by the drought-rehydration exercise at the flower pegging stage and drought stress was alleviated in the pod setting stage. We conclude that moderate CRDI is beneficial to peanut drought resistance for arid and semi-arid areas, and significantly promoted higher WUE.