Nitrogen Use Efficiency and Related Plant N Mechanisms in Corn & Sorghum.

Improvement of nitrogen use efficiency (NUE) in crops can be understood from the investigation of plant nutrient uptake process and the related nutrient utilization efficiencies. Understanding NUE changes and physiological strategies for corn and sorghum will facilitate improvements in plant N uptake and their related efficiencies, which can consequently impact crop productivity. The study of the grain N sources, herein understood as the 1) reproductive-stage shoot N remobilization (Remobilized N), 2) reproductive-stage whole-plant N uptake (Reproductive N), and 3) vegetative-stage whole-plant N uptake (Vegetative N), is a novel approach for investigating NUE changes from a plant physiological viewpoint. A scientific summary was performed with the goal of comparing NUE and N related efficiencies in corn versus sorghum. The primary outcomes for the comparison were: 1) Remobilized N was primarily associated with Vegetative N in both crops (with similar R²s, >0.6 units); 2) for the association established between Remobilized N and Vegetative N, a similar slope (0.6-0.7X) was documented for both crops, suggesting comparable physiological response for these plant processes and depicting similar potential for NUE improvement; 3) a trade-off between Remobilized N and Reproductive N was documented, suggesting a complex plant regulation processes (source:sink); 4) at the plant-scale, information adjusted by the specific plot plant-density value depicted similar slopes for corn and sorghum under low per-plant yield and N uptake values, but N internal efficiency (yield to N uptake slope) increased more than proportional for corn as compared to sorghum as both per-plant yield and N uptake levels increased. For corn, improvements in N uptake and NUE were merely based on yield improvement with lower grain N concentration; while less information is known about sorghum NUE improvement. Thus, the approach of comparing corn and sorghum NUE can provide guidance for future improvements in N related efficiencies and yield.