Morpho-Pheno-Physiological and Agronomic Traits Associated with Maize Response to Plant Density and Nitrogen.

The use of genotypes with improved performance for maize productivity and nitrogen use efficiency (NUE) at different management levels regarding plant crowding and N availability would be a great benefit to the whole cropping system framework. The identification of morpho-pheno-physiological traits responsible for maize yield gains is essential for physiology knowledge and maize breeding improvements. Two field experiments involving paired hybrids (i.e. with/without transgenic insect resistance) were conducted to investigate possible individual and interacting effects of plant density (PD) (low-54,000, medium-76,000 and high-104,000 plants ha^-1) and fertilizer N rate (low-0, medium-165 and high-330 kg N ha^-1) on maize yields and NUE. The objectives of this work were to: (i) identify morpho-pheno-physiological traits that were associated with high yielding maize plants in each experimental site under different hybrids, plant populations and N rates and (ii) assess physiological correlation between those traits. For these goals, morpho-pheno-physiological and agronomics traits were included in a genotype-by-trait biplot, which was constructed via principal components analysis (PCA) of a genotype-by-trait matrix containing standardized trait data by plotting the symmetrically scaled PC1 scores against the PC2 scores (explaining 58% of total variation). From these analyses, we observed - as expected - a high correlation between total N uptake and accumulation of aboveground biomass rather independent of the phenological stages. Surprisingly, stalk diameter at silking stage strongly correlated with kernel number at physiological maturity. Moreover, high correlations were observed between grain maize yield at physiological maturity and both SPAD values at silking stage and green leaf number during the post-anthesis period. Three “environmental” groups were identified by PCA according to plant crowding (one group comprised of low density population treatments; and the other two groups were mixed between medium and high stand density).