Differential Response of Maize Hybrids to Variability in Plant Emergence.

Plant emergence variability reduces grain yield of maize. The objective of this work was to investigate how maize hybrids respond to an increasing proportion of plants with delayed plant emergence. The experiments were carried out in Paraná Research Station of INTA during 2006-7 growing season. Two hybrids (DK682 and P300) were sown with hand-planters under four proportions of late emerged plants (0, 33, 50, and 67%) and two differences in plant development (2 and 4 leaves) between early plants (D-PLANTS) and late plants (d-plants). Plant grain yield (PY) and harvest index (HI) were measured for both group of plants. Crop grain yield (GY) was calculated by multiplying plant grain yield by plant density. Averaged across hybrids and proportions, the presence of d-plants reduced crop grain yield from 982 g m^-2 to 923 g m^-2 (2 leaves) and 836 g m^-2  (4 leaves). Both hybrids showed the greatest GY drop with one third of d-plants, however reduction was lower in DK682 than in P300 (10.3 vs. 20.1%). PY increased around 20% for both hybrids in D-PLANTS, and decreased between 38 (DK682) and 46% (P300) in d-plants. Greater tolerance to plant emergence variability of DK682 in respect to P300 was mainly attributed to a lower yield reduction and a greater harvest index in plants-d.