A two-year field experiment conducted under dryland conditions in semi-humid and drought-prone regions of China aimed to assess the effect of ammonia-oxidizing bacterial on maize water use efficiency and yield. A heterotrophic ammonia-oxidizing bacteria (HAOB) strain S2_8_1 was used. Six treatments were applied: (1) no irrigation + HAOB strain (DI), (2) no irrigation + blank culture medium (DM), (3) no irrigation control (DCK), (4) irrigation + HAOB (WI), (5) irrigation + blank culture medium (WM), and (6) irrigation control (WCK). Results revealed that HAOB treatment increased maize growth, yield, and water use efficiency over controls, regardless of whether the year was wet or dry. This improvement was attributed to the accelerated nitrification in the rhizosphere soil due to HAOB inoculation, which subsequently led to increased levels of leaf cytokinins. Overall, these findings suggest that HAOB inoculation holds promise as a strategy to boost water use efficiency and maize productivity in dryland agriculture. (c) 2024 Crop Science Society of China and Institute of Crop Science, CAAS. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NCND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).