Optimized planting density and nitrogen improve grain yield and water productivity in drip-fertigated maize through improved canopy function and source-sink balance.

Introduction: Balanced source-sink relations are essential for achieving high maize yield and water productivity, and maintaining post-silking green leaf area is critical for dry matter accumulation and yield formation in maize ( Methods: A two-year field experiment was conducted in northwest China with three planting densities (LD: 80,000; MD: 100,000; HD: 120,000 plants ha Results: Nitrogen application alleviated stress-induced premature leaf functional decline after silking, whereas increasing planting density accelerated the loss of effective leaf function. Both higher planting density and higher N rate significantly increased LAD. Compared with LD, MD and HD increased source growth by 23.0% and 19.4%, sink capacity by 23.9% and 15.2%, sink growth rate by 23.7% and 15.8%, and source-sink difference by 16.2% and 18.2%, respectively, indicating that sink limitation constrained further yield increases at higher densities. PLS-SEM showed that N mitigated premature leaf functional decline, while planting density negatively affected leaf functional maintenance. Planting density indirectly affected LAD via leaf functional decline (63.7% of the effect), whereas N rate and planting density directly influenced LAD (75.6% of the effect). LAD strongly affected source growth parameters (90.7%), which increased grain yield (89.0%) and source-sink parameters (73.4%), ultimately contributing to direct increases in grain yield (81.8%) and water productivity (74.3%). D2N3 achieved the highest grain yield, followed by D2N2, which significantly improved water productivity and irrigation water productivity. Discussion: Considering source-sink balance, water saving, and stable yield, D2N2 is recommended. These results improve understanding of how to achieve effective dense planting and high-yield maize cultivation under water-scarce conditions.