Physiological Dynamics of Maize Nitrogen Uptake and Partitioning in Response to Plant Density and Nitrogen Stress Factors: II. Reproductive Phase

Improved plant N utilization and partitioning is critical for future improvements in maize ( Zea mays L.) grain yield (GY). The overall research objective was to gain understanding of the physiological mechanisms underpinning biomass (BM), N uptake partitioning, and GY processes during the reproductive period for two maize hybrids grown at varying plant density (PD) (low is 54,000 plant ha −1 , medium is 79,000 plants ha −1 , and high is 104,000 plants ha −1 ) and N inputs (low is 0 kg N ha −1 , medium is 112 kg N ha −1 , and high is 224 kg N ha −1 ) over four site–years. At the community level, maize GY was maximized in both genotypes at the medium PD and highest N rate. At maturity, grain harvest index improved as the whole‐plant N uptake increased following a linear‐plateau model and, for N allocation, both grain and shoot N concentrations increased similarly as BM increased. Around flowering (±15 d), dry mass and N partitioning rates were unmodified by treatment factors. Treatment factors only marginally influenced potential kernel number near flowering. Allometric analyses confirmed a lack of treatment impact on whole‐plant N uptake and N remobilization coefficients. Greater reproductive‐stage N uptake was associated with superior ear strength (kernel number and weight) and late shoot N remobilization, but GY was also positively related to vegetative‐stage N uptake. Future research should identify genotypic variation for overcoming the documented N uptake trade‐off mechanisms (vegetative‐stage N uptake vs. shoot N remobilization) as related to the maize GY improvement process.