Plant-to-Plant Variability of Maize Crops Under Contrasting Nitrogen Availability and Plant Population Densities.

In maize crops, under fertilized and irrigated conditions (i.e. without edaphic resource limitations), increased plant population density, reduces the mean plant biomass and increases the variability (CV) of this trait. This plant-to-plant variability is early established and may be reduced if radiation availability per plant is increased during the pre-silking period. The objective of this work was to evaluate the effect of N x plant population density on (i) the mean values of plant biomass at different ontogenic stages, plant growth rates during the vegetative period, pre-silking period and around silking, and kernel set, (ii) the CV of mentioned traits and (iii) the relationships among variables. Field experiments were conducted during two growing seasons using a factorial combination of (i) two N levels (N₀: no N added; N₂₀₀: 200 kg N ha^-1 applied at V₆), (ii) two maize hybrids of contrasting tolerance to increased stand density (tolerant: AX820CL-MG; intolerant: AX877CL-MG), and (iii) two (9 and 12 pl m^-2) or three (6, 9, and 12 pl m^-2) stand densities. At any plant population density, N fertilization reduced the initial plant-to-plant variability and increased individual plant biomass. Positive correlations among plant growth rates of the different periods were found, but these correlations resulted higher for the non-fertilized crops. Under the most stressful conditions AX877CL-MG exhibited more barrenness plants, mainly by a higher plant-to-plant variability and the lower biomass partitioning to the ear around silking.