Resource Availability and Intra-specific Competition in Maize: An Eco-physiological Perspective.

As with most plant species, maize (Zea mays L.) encounters both intra- and inter-specific competition for requisite resources throughout a growing season.  While multiple aspects of inter-specific competition have been previously examined in maize (e.g., maize-weed interactions), relatively few investigations have delved into the eco-physiological and agronomic aspects of maize-maize interactions.  Furthermore, no study to date has intensively investigated the season-long, eco-physiological dynamics of maize intra-specific competition with respect to varying resource availability.  In this 3-yr experiment (2005-2007), the growth and development of individual plants was measured from seedling emergence to physiological maturity using numerous morpho-physiological parameters.  These parameters included, but were not limited to, plant height, stalk diameter, vegetative and total biomass, leaf area index (LAI), anthesis-silking interval (ASI), leaf greenness (SPAD), grain yield, total kernel number, individual kernel weight, and harvest index (HI).  Using three plant densities (54,000, 79,000, and 104,000 plants ha^-1) and three nitrogen (N) application rates (0, 165, and 330 kg ha^-1), the impact of varying resource availability was examined each growing season for two modern hybrids.  To determine the form and magnitude of intra-specific competition, we used data analysis techniques commonly employed by ecologists and economists alike.  Such analyses revealed intense asymmetric competition when resources were severely limiting (i.e., 104,000 plants ha^-1, 0 kg ha^-1), with the proportion of “dominated” plants relatively large in such situations.  In this presentation, we will further discuss the results of these analyses as they relate to the formation and seasonal dynamics of maize plant hierarchies.