Maize Basal Stem Diameter: Correlations with Per-Plant and Canopy-Level Performance Under Multiple Plant Density and Nitrogen Regimes.

Thoroughly understanding the eco-physiological responses of maize (Zea mays L.) to environmental and agronomic-management factors is of considerable importance for improving the stress tolerance and nitrogen use efficiency (NUE) of the species.  Garnering this in-depth comprehension often requires intensive field phenotyping.  Despite evidence that individual plant responses and interactions can extensively characterize and uniquely explain canopy-level responses, maize field phenotyping efforts have primarily focused on canopy behavior and not individual plant performance and/or plant hierarchy dynamics.  This may have resulted from the general absence of a rapid, low-cost, multi-stage, per-plant morpho-physiological measure that identifies, characterizes, and/or predicts (i) per-plant vegetative and reproductive productivity, (ii) plant hierarchy dynamics, and (iii) canopy-level performance.  Thus the objective of this intensive 3-year field study was to find a measure that met each of these criteria.  This phenotyping experiment examined both per-plant and canopy-level responses to N application (0, 165, and 330 kg N ha^-1) at multiple plant densities (54,000, 79,000, and 104,000 plants ha^-1) for two commercial hybrids.  The growth and development of individual plants was measured from VE to R6.  Per-plant measurements included (but were not limited to) plant height, basal stem diameter, vegetative and total biomass, leaf area, anthesis-silking interval, leaf chlorophyll content, grain yield, total kernel number, individual kernel weight, and harvest index.  Canopy-level measurements included (but were not limited to) grain yield and NUE.  Results indicated that, whether taken at V14, R1, R3, or R6, (i) a plant’s basal stem diameter was a good predictor of that plant’s biomass and grain yield, (ii) mean basal stem diameter for a canopy’s population of plants correlated with that canopy’s overall productivity, and (iii) per-plant basal stem diameter helped characterize season-long plant hierarchy dynamics.  In this presentation, we will further highlight these results and detail how such findings impact maize improvement programs.