Water stress poses a significant constraint on crop productivity in arid regions. A 2-year field experiment was conducted using a split-factorial layout within a randomized complete block (RCB) design to determine whether the combination of Azospirillum brasilense and Pseudomonas fluorescens (plant growth-promoting rhizobacteria [PGPRs]) with organic matter (OM) can mitigate the negative impacts of water stress on the grain yield of triticale (xTriticosecale Wittmack), as well as on water use efficiency for grain (WUEg) and biomass (WUEb). Irrigation treatments, including full irrigation (IRN) and post-milking deficit irrigation (IRD), were assigned to the main plots. Subplots were allocated to different OM sources (no OM, wheat residue, and its biochar) and nitrogen-phosphorus (N-P) sources, viz: chemical N-P fertilizer and integrated N-P fertilizer (50% chemical N-P fertilizer combined with PGPRs). Results indicated that IRD led to a significant decrease in grain yield (60.1%) and, ultimately, WUEg (43.4%) without OM application. However, using biochar resulted in the lowest reductions in these traits (41.1% and 14.6%, respectively) compared to the other OM treatments. The application of integrated N-P fertilizer resulted in an increase in grain yield, WUEg, and WUEb, across all types of OM compared to chemical N-P fertilizer. Notably, the most substantial improvements were observed with the application of biochar, which enhanced grain yield, WUEg, and WUEb by 24.5%, 27.7%, and 18.6%, respectively. Additionally, the application of integrated N-P fertilizer mitigated the decline in average grain weight, a crucial factor influencing the grain yield of triticale, under post-milking water stress conditions. Finally, integrated N-P fertilizer in conjunction with biochar is recommended for arid regions facing irrigation water restrictions during the grain-filling stage of triticale.