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 a rchitecture, which has to be defined in terms of the size, shape and orient ation of shoot components. Cultural practices that improve the efficiency o f Light interception affect canopy architecture by modifying such component s. Our objectives were to: (i) determine the nature and timing of leaf grow th responses to plant population and row spacing; (ii) analyze light attenu ation within fully developed maize canopies. Field experiments were conduct ed 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 silt y clay loam soils (Typic Argiudoll) that were well watered and fertilized. Four maize hybrids of contrasting plant type were grown at three plant popu lations (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 spaci ng. 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, prob ably triggered by a reduction in the red:far-red ratio of light within the canopy. An interaction between hybrid and plant rectangularity on leaf azim uthal distribution was determined, with one hybrid displaying a random azim uthal leaf distribution under most conditions. This type of hybrid was defi ned as rigid. The other hybrids showed modified azimuthal distribution of l eaves in response to plant rectangularity, even at very low plant populatio ns. These hybrids were defined as plastic. Once maximum leaf area index (LA I) was attained light attenuation did not vary among hybrids and row spacin g for plant populations greater than or equal to9 plants m(-2) (k coefficie nt: 0.55 and 0.65 for 9 and 12 plants m-2, respectively). A more uniform pl ant distribution increased light attenuation (k coefficient: 0.37-0.49) onl y when crop canopies did not reach the critical LAI. (C) 2001 Elsevier Scie nce B.V. All rights reserved.