Increasing seeding density under limited irrigation improves crop yield and water productivity of winter wheat by constructing a reasonable population architecture

Favorable crop population architecture is the foundation for obtaining high crop yields and water productivity (WP) under limited irrigation. A field experiment was conducted at Wuqiao Experimental Station from 2015 to 2018 using the ‘Nongda399′ wheat variety under the four seeding density and three irrigation schemes to explore the population architecture, canopy apparent photosynthesis (CAP), organ contribution, yield, and WP of winter wheat (Triticum aestivum L.). Compared with conventional high-yield cultivation (SD1W3), the water-saving cultivation (SD3W1) obtained a comparable yield meanwhile improved the WP in the range of 14.2–39.2%. The non-significant change in the yield under SD3W1 was primarily due to the increasing seeding density under W1 irrigation treatment, which improved the spike number and grains per unit area, especially the main stem spike, and had no significant effect on the thousand kernel weight (TKW). Increases in grain yield was generally caused by increases in CAP by constructing a reasonable canopy architecture with higher leaf area index (LAI) and non-leaf area index (NLAI) of the total canopy and upper strata, especially the spike area index (SAI) of the upper strata. Therefore, more light was intercepted by spikes, which improved the contribution of spike photosynthesis to yield. Increasing the seeding density also improved the assimilate remobilization contribution (RC) of pre-anthesis and decreased the post-anthesis leaf photosynthesis contribution to yield. Increasing the seeding density under limited irrigation improved the root length density (RLD), especially in 120–200 cm soil layer, which increased the absorption and use of deep soil moisture and improved WP. Overall, when sowing time from October 10–20, the appropriate seeding density of approximately 525–600 plants m⁻² with 75 mm of irrigation at the jointing stage was the best cultivation practice for saving water and obtaining a comparable yield and a high water productivity of winter wheat in the North China Plain (NCP).