SPATIAL REORIENTATION OF MAIZE LEAVES AFFECTED BY INITIAL PLANT ORIENTATION AND DENSITY

Modelling crop architecture and light interception by maize usually as sumes a uniform distribution of leaf azimuth. A developmental study of the spatial display of the shoot structure was carried out during the vegetative growth through a field experiment with four treatments: tw o initial plant orientations (one treatment with the first leaves of a ll plants initially perpendicular to the row direction and another tre atment with the first leaves of all plants initially parallel to the r ow direction) and two densities (about 10 plants/m(2) and 20 plants/m( 2)). The position of each leaf was characterized over time using three parameters: leaf azimuth, leaf base inclination, and leaf insertion h eight. A circular data analysis was necessary to study leaf angle (azi muth, inclination). The first leaves grow in the same vertical plane u ntil leaf 8 or 9. For these leaves, there was a low dispersion of leaf azimuths around the initial plant azimuth. For upper leaves however, the dispersion of leaf azimuths increased, tending to a uniform distri bution for leaves 12 to 14. We observed no effect of initial plant ori entation on final leaf mean azimuths. The only important effect of ini tial plant azimuthal clumping was to increase the trend toward azimuth al dispersion. For an individual leaf, azimuthal movements occurred ma inly during the growing period, but some movements could occur between ligulation and silking too. These movements were caused at least in p art by a twisting of the internodes, and may also result from the twis ting of the sheaths and the nodes. These results, especially for the u pper leaves, are in contrast with those of previous workers with compa rable experimental design, but in growth chamber conditions, in which leaves tended to be orientated more and more perpendicular to the row, due to internode torsion. The effects of initial plant orientation on leaf inclination and height were less spectacular. Initial plant orie ntation and density had a small effect on leaf base inclinations. An e ffect of density was observed only on leaf insertion heights, but no i ntercalation of leaves between adjacent plants was noticed. (C) 1997 E lsevier Science B.V.