Soil water is a major limitation to high crop production on the Loess Plateau of China. Straw incorporation is often suggested to promote soil water retention and grain production. Despite the rising number of studies on straw application to soil, the demonstrated merits for straw with lower C: N ratios and varying lengths remain unknown. A five-year field experiment was conducted to explore the effect of ammoniated long or short straw incorporated into the soil on soil water storage (SWS), leaf area index (LAI), intercepted photosynthetically active radiation (PARi), aboveground biomass, evapotranspiration (ET), grain yield, and water use efficiency (WUE). The three treatments were: (i) control (CK: no straw), (ii) ammoniated long straw (50 mm) incorporated into the soil (ALSI), and (iii) ammoniated powdered straw (1 mm) incorporated into the soil (APSI). Compared to the CK plots, the APSI plots increased maize SWS and soil available water (SAW) by 0.2–5.1 % and 1.2–5.7 %, respectively, across the five cropping seasons, and had higher WUE and lower ET and evapotranspiration rate (ETR). The coefficients of variation (CV)—indicating the stability of aboveground biomass, grain yield, and harvest index (HI) in the three treatments across five growing seasons—were ranked as follows: APSI < ALSI < CK. The ammoniated powdered straw incorporated into the soil improved soil water utilization (i.e., conserved more water) and increased maize grain production better than the other two treatments in the rainfed region of the Loess Plateau of China.