Plant population density, row spacing and hybrid effects on maize canopy architecture and light attenuation

Light attenuation within a row crop such as maize is influenced by canopy architecture, which has to be defined in terms of the size, shape and orientation of shoot components. Cultural practices that improve the efficiency of Light interception affect canopy architecture by modifying such components. Our objectives were to: (i) determine the nature and timing of leaf growth responses to plant population and row spacing; (ii) analyze light attenuation within fully developed maize canopies. Field experiments were conducted at Pergamino (33 degrees 56 'S, 60 degrees 34 'W) and Salto (34 degrees 33 'S, 60 degrees 33 'W), Argentina, during 1996/1997 and 1997/1998 on silty clay loam soils (Typic Argiudoll) that were well watered and fertilized. Four maize hybrids of contrasting plant type were grown at three plant populations (3, 9 and 12 plants m(-2)) and two row spacings (0.35 and 0.70 m). Plant population promoted larger changes in shoot organs than did row spacing. As from early stages of crop growth, leaf growth (VB-VB) and azimuthal orientation (V-10-V-11) were markedly affected by treatments. Modifications in shoot size and leaf orientation suggest shade avoidance reactions, probably triggered by a reduction in the red:far-red ratio of light within the canopy. An interaction between hybrid and plant rectangularity on leaf azimuthal distribution was determined, with one hybrid displaying a random azimuthal leaf distribution under most conditions. This type of hybrid was defined as rigid. The other hybrids showed modified azimuthal distribution of leaves in response to plant rectangularity, even at very low plant populations. These hybrids were defined as plastic. Once maximum leaf area index (LAI) was attained light attenuation did not vary among hybrids and row spacing for plant populations greater than or equal to9 plants m(-2) (k coefficient: 0.55 and 0.65 for 9 and 12 plants m-2, respectively). A more uniform plant distribution increased light attenuation (k coefficient: 0.37-0.49) only when crop canopies did not reach the critical LAI. (C) 2001 Elsevier Science B.V. All rights reserved.