To date, little attention has been paid to the effects of lower position leaves on root function and N uptake in maize. This study was conducted to analysis the relationship between lower leaf senescence and root function in different plant population (67,500 plants ha-1 , 90,000 plants ha-1). We used the maize varieties DengHai661 (DH661) and ZhengDan958 (ZD958) in field and soil column experiments to unravel this physiological puzzle. The field experiment evaluated their effects on N accumulation and grain yield. Relative to the low plant population, the high plant population reduced leaf area (52.6-69.2%), and the root biomass (25.5-31.8%) per plant. Grain weight and the number of grains per ear were also negatively affected. Biomass and grain yield generally increased (P < 0.05) with increasing plant population. The grain yield of DH661 and ZD958 increased by 8.1% and 10.1% in 2015, and 7.5% and 13.0% in 2016, respectively. The N accumulation of two varieties postsilking decreased. In the soil column experiments, we found that lower leaf senescence suppressed root growth, N uptake, and altered N partition, thereby decreasing green leaf area and ultimately affecting grain yield. Grain yield in DH661 and ZD958 decreased by 5.8 and 8.6%, respectively. Our results suggest that delaying lower leaf senescence in high plant population would be conducive to maintaining the N-uptake ability of roots, higher canopy photosynthetic capacity, and the building of grain sink to obtain higher yields.

High grain yield and N use efficiency are key goals of crop production. Increasing planting density and supplying adequate N application are important agronomic practices to increase maize grain yield. However, little is known about the interaction between the planting density and N application rate of high-yield maize under mulch drip irrigation. The objectives of this study were to determine the impacts of planting density and N application rate on the grain yield, economic return, nitrogen partial factor productivity (PFP N), and nitrogen agronomic efficiency (AE N) of super high-yield maize under mulch drip irrigation in Northwest China. To achieve this, field experiments were conducted in 2017 and 2018 in Qitai farm, Xinjiang. The experiments included four N application levels−no nitrogen (N0), and 270 (N1), 360 (N2), and 450 kg N ha −1 (N3)−and five planting densities−7.5 (D1), 9.0 (D2), 10.5 (D3), 12.0 (D4), and 13.5 plants m −2 (D5). It was found that the N2D4 treatment obtained the highest grain yield (21.5−21.6 t ha −1) and economic return (US$3,399.7−$3,440.3 ha −1) and the relative higher PFP N (59.7−60.1 kg kg −1) and AE N (23.7−25.1 kg kg −1). The PFP N and AE N declined with increasing N application and varied according to a quadratic relationship with increasing planting density. Therefore, a reasonable increase of planting density and an appropriate reduction of N application combined with integrated irrigation−fertilization technology under mulch drip irrigation cannot only obtain high maize yield and economic return but can also improve the N utilization efficiency.

Under high‐density planting, mixed cropping planting pattern can potentially optimize maize (Zea mays L.) canopy architecture and ultimately improve grain yield. The objectives of this study were to evaluate the effects of three plant patterns combined with three plant population densities (67,500, 82,500, and 97,500 plants·ha−1) on canopy architecture and grain yield. Zhengdan 958 (ZD958) and Denghai 605 (DH605) were used as experimental materials. Three different planting patterns were: mixture (M), random sowing after mixing seeds of the two hybrids in the same proportion; 1:1, one row of ZD958 and one row of DH605; and two monoculture systems, SZD958 and SDH605, as controls. A 3‐yr study demonstrated that the mixed cropping treatments (M and 1:1) at low density (LD) showed no significant difference on light transmission, leaf area index (LAI), canopy apparent photosynthesis (CAP), and canopy respiration (CR), compared with the two monocultures. However, at a medium and high density (MD and HD), mixed cropping was characterized with higher light transmission to the ear and lower layers of the canopy during grain filling than that of monoculture treatments, while no significant differences between M and 1:1 treatments. Moreover, mixed cropping treatments maintained a higher LAI, CAP, lower CR, and increased the whole and post‐silking dry matter accumulation. Grain yields were higher under mixed cropping at MD and high density (HD), while no significant differences between M and 1:1 treatments. Relative to SZD958 and SDH605, the grain yields in the M treatment were 10% and 8% higher at MD, and 7% and 5% higher at HD, respectively. Mixed cropping optimized the canopy structure, maintained higher LAI and CAP during the grain filling period, reduced respiration, and increased aboveground dry matter at maturity. These improvements also result in higher grain yield. Core Ideas Mixed cropping facilitated the formation of a high‐efficiency canopy structure. Mixed cropping delayed the rate of leaf senescence, maintained higher LAI and CAP during the grain filling period. Mixed cropping increased aboveground dry matter weight at physiological maturity, and ultimately led to higher grain yield, especially medium density.