Morphological Variation of Maize Cultivars in Response to Elevated Plant Densities

Increasing plant density is a common method for increasing maize (Zea mays L.) yield. However, the yield increases are limited by light competition and mutual shading that occur within close canopies. The objectives of this 2-yr field experiments were to determine the effect of plant density on maize plant morphology, canopy structure, and canopy light distribution. The leaf length, leaf width, leaf area and leaf area index (LAI) increased from both the top and the bottom of the canopy. The leaf angle generally decreased from the bottom to top of the canopy; however, the leaf orientation value (LOV) displayed the opposite trend. The leaf length and width decreased as plant density increased. The decrease in width was greater than in length. Changes in leaf dimensions caused leaf area to decline. Increasing plant density resulted in a decrease in leaf angle; however, an increase in LOV. Changes in the leaf canopy were more affected above the ear compared to below the ear as plant density increased. This made the leaves above the ear more upright as plant density increased. The leaf spacing below the ear increased as the plant increased, causing the ear height, plant height coefficient to increase. Light intensity within maize canopy decreased with increasing density. The results indicate that maize adapts to increasing density by (i) increasing leaf spacing below the ear and LOV above the ear and by (ii) reducing leaf width and leaf angle. These changes allow more light transmission into the mid-and lower canopy.