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.