Why Do Maize Hybrids Respond Differently to Variations in Plant Density?

Received for publication July 7, 2006. Maize (Zea mays L.) grain yield responds greatly to plant density (D). However, the hybrid–plant density interaction usually found is not well understood. The objective of this work was to analyze responses of different maize hybrids to D considering their biomass plasticity and reproductive partitioning. Responses to D were analyzed during 2 yr in three hybrids with contrasting maturity and plasticity. The relationships between aboveground biomass per plant at maturity (Bp) and D and between grain yield per plant (Yp) and Bp were used to explain hybrid responses to D. Optimum D ranged from 10.3 to 13.7 plants m^–2. The hybrid with the lowest optimum D presented the greatest biomass plasticity and reproductive partitioning. Increasing D produced an increase in biomass production per unit area in all hybrids. Contrarily, a greater harvest index (HI) with increasing D was only observed in the hybrids with the least plasticity. Increments in grain yield with increasing D were, in all cases, more associated with increases in biomass production than with increments in HI. Parameters of the equations Bp – D and Yp – Bp were related to optimum D. To validate these relationships, an independent data set was used. Some of these parameters were associated with biomass plasticity and reproductive partitioning and could be used to explain and estimate the responses to D.