Mathematical Characterization of Leaf Shape and Area of Maize Hybrids

Abstract

Measurement or estimation of leaf area is essential for simulation of light interception and photosynthate production. Leaf shape is an important factor in describing how leaf area is distributed in the canopy. When defined mathematically, leaf shape can be used to calculate leaf area of individual leaves as well as how leaf area varies along the length of the leaf. The objective of this study was to evaluate several methods used to describe leaf shape (the variation in leaf width with distance from the ligule or stem) and to analyze variations in shape coefficients. Measurements of leaf width every 10 cm along fully expanded leaves were made over a number of years, sites, plant densities, and nitrogen treatments with normal, leafy, and reducedstature hybrids. These measurements were fitted to a number of polynomial equations which related leaf width to distance from the ligule. Leaf area was calculated by integrating these equations. In all, 10 methods were used to calculate areas of individual leaves, but one method, based on a second order polynomial equation which could easily be integrated for total leaf area or area along the leaf, was chosen as a standard. All other methods were compared with this standard and leaf area estimates were found to be similar (R2 > 0.98). Planimeter measurements of individual leaf area also compared well with estimates using the standard method (R2 = 0.96) hut planimeter measurements had more scatter than estimated values. The most useful equation was the second order polynomial with two dimensionless shape coefficients using maximum leaf width and total length. Integrating this equation produced the well known length × maximum width × alpha equation for calculating leaf area where alpha was 0.743 for all hybrids and 0.734 for normal hybrids. A method was developed to use this equation for calculating leaf area as a function of leaf length.