The Proceedings of the International Plant Nutrition Colloquium XVI

Although maize (Zea mays L.) routinely experiences both intraand interspecific competition for limited resources, most plant-plant interaction studies have principally focused on maize-weed interactions. Thus very few investigations have considered the impacts of plant crowding and nitrogen (N) availability on maize intra-specific competition. The primary objective of this two-year field study near West Lafayette, IN was to investigate the per-plant eco-physiological responses of modern maize genotypes to varied N availability (0, 165, and 330 kg side-dress N ha-1) at low and high plant densities (54,000 and 104,000 plants ha1, respectively) by measuring responses among dominated [lowermost 25% perplant grain yield (GYP)], intermediate, and dominant (uppermost 25% GYP) individual plants in each treatment combination. Parameters measured at the per-plant level included R1 green leaf area (LAP), R1 SPAD, anthesis-silking interval (ASIP), GYP, R6 total aboveground biomass (TBP), and harvest index (HIP). In both years, severe intra-specific competition for soil N in the highly crowded, low-N environment resulted in low R1 LAP and SPAD values, high ASIP values, and reduced GYP, R6 TBP, and HIP values, particularly among dominated plants. Intense competition in this environment also led to (i) high dominant group/dominated group mean ratios for most parameters; (ii) high plant-to-plant variability for R1 SPAD, ASIP, GYP, and HIP; and (iii) high frequencies of barren and low-yielding plants. Insufficient N at high plant densities thus encouraged the formation of plant hierarchies composed of markedly dominated individuals with diminished source capability and severely impaired biomass partitioning to developing grain.