Context: Soil erosion and degradation severely threaten rain-fed maize production in China's semi-arid Loess Plateau. However, quantitative assessments of tillage optimization strategies and their threshold effects on yield and water use efficiency (WUE) remain limited. Objectives: Evaluate tillage impacts on maize yield and WUE, identify critical soil thresholds, and assess natural vs. management drivers. Meta-analysis included 374 observations from 39 studies on yield, and 237 observations from 25 studies on water-use efficiency. Results: Compared with no tillage (NT), the effects of tillage practices varied: deep ploughing (DP), ridge tillage (RI), no tillage with straw mulching (NTS), rotational tillage (RO), and subsoiling (SS) increased maize yield by 3.96 %-11.02 % and WUE by 4.65 %-14.64 %. Rotary tillage (RT) and plough tillage (PT) showed small, nonsignificant increases in yields (2.3 % and 0.65 %, respectively) and had no significant positive impact on WUE. Neutral pH (6.5-7.5), optimal bulk density (1.00-1.25 g cm(-3)), high soil organic carbon (>5.8 g kg(-1)) and total nitrogen (>1.5 g kg(-1)) boosted yield (4.56-16.93 %) and WUE (3.78-13.41 %). Management measures and natural factors also influenced yield and WUE. Highest yield gains (4.55-6.31 %) and WUE improvements (3-6.28 %) occurred in regions with >400 mm rainfall, <= 1000 m elevation, >2200 h sunshine, >150 frost-free days, >1500 mm evaporation. Specifically, lower temperatures (<= 10 C-degrees) favored yield, while higher temperatures (>10 C-degrees) resulted in slightly higher WUE. Optimal practices included >150 kg ha-1 nitrogen and >60,000 plants ha(-1) density. Therefore, tillage practices should be chosen based on local conditions. Additionally, random forest models identified nitrogen application as primary yield drivers, while pH and BD dominated WUE. Conclusion: DP, RI, and NTS are the most effective practices. Their efficacy is maximized under specific thresholds. Furthermore, nitrogen application serves as the primary driver for yield, whereas soil properties (pH and BD) regulate WUE. Implications: We recommend prioritizing DP to alleviate soil compaction and NTS to conserve moisture in arid areas. These practices should be coupled with high planting density and nitrogen management to achieve resource-efficient agriculture in the Loess Plateau.