Moderate winter irrigation reduction improves maize water productivity under green manure incorporation by optimizing root distribution and water consumption

In arid and semi-arid regions, winter irrigation is a crucial practice for ensuring crop growth, yet it exacerbates water resource consumption. Green manure mulching has been demonstrated to conserve soil moisture while enhancing soil fertility. However, the reduction threshold for winter irrigation and its coordinated effects on soil water distribution, evapotranspiration partitioning, root traits, and yield formation under green manure incorporation remain insufficiently quantified. The study was conducted as a field experiment between 2024 and 2025 at the Wuwei Oasis Agricultural Experimental Station, China. Six winter irrigation levels were established under green manure incorporation ((i) Conventional winter irrigation (I 100 ), (ii) 20% reduced (I 80 ), (iii) 40% reduced (I 60 ), (iv) 60% reduced (I 40 ), (v) 80% reduced (I 20 ), and (vi) no winter irrigation (I 0 )) to evaluate maize yield, water use characteristics, and the underlying mechanisms. The results showed that compared with the I 100 , I 60 treatment decreased pre-sowing soil water storage (SWS) but effectively induced pronounced root expansion into the 20–60 cm layer. This root distribution pattern was accompanied by improved canopy coverage, reduced soil evaporation (E), and a higher transpiration-to-evapotranspiration ratio (Tr/ETa). Concurrently, I 60 was associated with higher soil water storage in the 50–110 cm layer from the milk stage (R3) to maturity stage (R6), indicating a more favorable vertical soil water distribution within the monitored profile. Moreover, the coordinated optimization of root architecture and activity (RA) under I 60 supported efficient dry matter accumulation (DMA), providing a physiological basis for yield stability and enhanced water productivity (WP). In conclusion, reducing winter irrigation by 40% under green manure incorporation enhances water productivity and stabilizes yield by optimizing water consumption characteristics and root spatial distribution. These findings are based on a system with green manure incorporation; the response to winter irrigation reduction in systems without green manure remains to be evaluated.