Abstract: 【Objective】Drought and water shortage are the main limiting factors for dryland agricultural production on Loess Plateau of China, and studies of the effects of film mulching and close planting and hybrids on dryland corn yield and water use efficiency (WUE) are of benefit to understand the relationship of future grain yield increase and water environment safety.【Method】A 4-year field experiment with three replications was conducted in Pengyang county, Ningxia, a hilly and gully region on China’s Loess Plateau, in continuous spring corn seasons from the year 2012 to 2015, and a randomized design was used with full film ridge-furrow cover (FPRF) and half film-flat cover (HPFC) , three corn hybrids of XY335 and JX1 with close planting and mid-late mature, and JD4 with spaced planting and early mature, and three plant densities of 4.5×10⁴ (Low), 6.75×10⁴ (Middle) and 9.0×10⁴ (High) plants/hm². The area of each plot was 6.5 m ´ 3.3 m. Soil water contents were determined at main crop stages in soil depths of a 200 cm with 20 cm depth as a soil layer. Seasonal ET amounts were calculated with growing season precipitation (precipitation received from planting to harvesting) and soil water changes. Grain yields in all plots were determined by hand-harvesting 12 m². Soil moisture contour maps of 2012-2015 were drawn using SURFER V11 software. 【Result】Experimental factors highly affected dryland film mulched corn yield and water use, but the order of influence on grain yield and WUE was corn density ＞ film mulching pattern ＞ corn variety. With year’s type from dry years to normal and rainy years, grain yield increased from 7.72 and 8.79 t·hm^-2 to 11.86 to 11.15 t·hm^-2, but the highest WUE value was obtained in normal year not in rainy year. When corn density increased from 4.5 ×10⁴ to 6.75 ×10⁴ plants/hm², ETs, grain yield and WUE increased by 10.6 mm, 20.0% and 3.45 kg×mm^-1×hm^-2, and the density improved from 6.75×10⁴ to 9.0×10⁴ plants/hm², ETs did not increase again and grain yield and WUE increased by 12.0% and 2.97 kg×mm^-1×hm^-2, respectively. Average grain yield of corn and WUE in FPRF increased by 15.72% and 21.09% compared with that in HPFC. Grain yield and WUE of JX1 and XY335 hybrids, with close planting and middle-late mature, increased by 15.46% -24.45% and 13.35% -15.55% compared with that of JD4 hybrid with low density and early mature. Whatever rainfall in the four years, profile soil water content at 0-200 cm layers during crop growing season was always higher in the FPRF than in the HPFC treatment, particularly the FPRF stored more than 50-90 mm soil water at the 0-200 layers in grain filling period, which played an important role in drought-resistance and WUE increase during serious summer drought. More importantly, the FPRF with significant corn yield increase by close planting did not deplete much soil water, yet not resulted in deep dry soil layers formation whether normal and rainy or dry year, and negative effects on soil water cycle were not observed in the FPRF. However, a dry soil layer with less than 8% of soil water was formed significantly in the HPFC treatment at deep layers in dry years, and dry soil thickness increased and it’s scope extended as corn growth. 【Conclusion】On the basis of film mulching with density of 5.3×10⁴ plants/hm² currently, the package of full ridge-furrow film mulching and close planting hybrids and density improvement of 1.5×10⁴ plants/hm² will be a key technique for sustainable grain yield increase of dryland corn and high efficient use of water in dryland area of annual rainfall over 450 mm, and the yield-increasing techniques with close planting did not cause deep dry soil layers formation.

Key words: dryland corn, film mulching, close planting and grain yield increasing, water use efficiency, soil water