Ear demand in Argentinean maize hybrids as affected by plant density and year of release.

Prior studies, conducted in Argentina until 1993, determined that maize grain yields have dramatically increased as a result of increased ear demand. The product of kernel number per square meter and kernel growth rate during effective grain filling period is an indicator of ear demand. The effects of plant density on ear demand and its components remain still not clear. The objective of this study was to assess ear demand and its components, and their interaction with plant density in maize hybrids released in the last 20 years. An experiment was conducted at Balcarce, during the 2010-2011 growing season, in order to compare ear demand of an older versus a recently released maize hybrid. An older hybrid released in 1993 and a newer hybrid released in 2010 both with the similar grain filling duration, were grown at three plant densities (5; 9.5; and 14 pl m-2). Kernel growth rate during effective grain filling period, kernel number per plant, kernel weight and grain yield were measured and ear demand calculated as the product of kernel number per square meter and kernel growth rate during effective grain filling period. Grain yield and ear demand were significantly greater in the 2010 hybrid across plant densities, and both parameters were strongly associated with number of grains per square meter. Kernel growth rate, duration of effective grain filling period, and kernel weight remained fairly constant across hybrids and plant densities. Also, grain yield, number of grains per square meter and ear demand were greater in 9.5 pl m-2 and 14 pl m-2 compared to the lowest density, in both hybrids. Our data show that ear demand increased in the last two decades, that kernel number is the most important mechanism involved in this response and that ear demand depends on plant density.