Physiological Dynamics of Maize Nitrogen Uptake and Partitioning in Response to Plant Density and N Stress Factors: I. Vegetative Phase

From a physiological perspective, field studies that quantify the influence of plant density (PD) and N rate on biomass (BM) and N uptake are needed to build more functional partitioning models for maize ( Zea mays L.). The overall goal was to quantify the effects of maize hybrid (two genotypes), PD (low = 54,000; medium = 79,000 and high = 104,000 pl ha ‐1 ), and N rate (low = 0, medium = 112 and high = 224 kg N ha ‐1 ) on the organ‐specific dry mass and N allocation, and on the resource capture (ratio of leaf area index [LAI] to BM), and resource use efficiency (ratio of N uptake to LAI) parameters, during the vegetative phase at four site‐years. Allometric analyses revealed that the resource capture was primarily affected by the PD, and the resource use efficiency by the N rate. The stoichiometry between leaf and stem dry mass was unaffected by the treatment factors, but no isometry was documented (greater BM to the stem than leaf). The N rate primarily modified the leaf and stem N concentrations (0N vs. 112–224N). With respect to resource use efficiency, modifications in the leaf N content per unit of LAI were joint outcomes of changes in leaf mass and %N (N concentration). In contrast, physiological changes in the stem N content per unit of LAI were more dependent on changes in the stem %N (greater N storage capacity) rather than in the stem mass. Intensifying competition with neighboring plants reduced per‐plant mass similarly in both leaf and stem structures, and improving N supply was proportionately more beneficial in maintaining plant mass and stem %N at high PD during vegetative growth.