Intraspecific Competition in Corn: Nitrogen Rate and Plant Density Effects on Growth and Developmental Uniformity.
Christopher Boomsma, Purdue University, 915 W. State Street, Lafayette, IN 47909 and Tony Vyn, Purdue Univ, Dept of Agronomy, 1150 Lilly Hall, 915 W State St., West Lafayette, IN 47907-1150.
The optimum plant population for maximum grain yield in corn (Zea mays L.) has increased steadily over the past 70 years as a result of the improved high plant density tolerance of modern hybrids. Higher plant densities result in greater intraspecific competition between individual plants potentially leading to increased plant-to-plant variability for grain yield and other morpho-physiological traits. Past studies have often emphasized that stand uniformity is essential for high productivity as it results in reduced intraspecific competition. This study seeks to determine the effects of nitrogen rate (0, 170, and 340 kg ha-1), plant population (54,000, 79,000, and 104,000 plants ha-1), and genotype (hybrids Pioneer 31G68 and 33N09) on the growth and developmental uniformity and associated hierarchical distribution (i.e., dominated vs. dominating plants) of individual corn plants within the canopy. In 2005, the growth and development of individual plants was assessed via the measurement of numerous parameters from seedling emergence to physiological maturity. Per-plant variability in leaf SPAD was greater at higher populations, presumably because of greater intraspecific competition for available soil nitrogen. Variability in per-plant grain yield rose with increasing plant density for each nitrogen rate, but decreased with increasing nitrogen availability within each population level. Per-plant variability was consistently greater for hybrid Pioneer 33N09 than for hybrid Pioneer 31G68. Averaged across nitrogen rates and hybrids, barrenness increased with increasing plant density. Additionally, barrenness was greater for the 0 kg ha-1 than the 340 kg ha-1 nitrogen rate at 79,000 and 104,000 plants ha-1, but less for the 0 kg ha-1 than the 340 kg ha-1 nitrogen rate at 54,000 plants ha-1. These results suggest that adequate nitrogen availability is critical for reducing plant-to-plant variability and the number of dominated plants resulting from intraspecific competition at high plant densities.