Leaf Area Development in Field‐Grown Maize 1

Leaf area is important for crop light interception and therefore has a large influence on crop yield. In this study, a method was devised to characterize and predict the development process of maize ( Zea mays L.) leaf area by separating the process into time of appearance of each mature leaf (leaf stage) and leaf area of each mature leaf (leaf expansion). Leaf area was measured for several years on each of two soil types [a sandy loam of the Uplands association (Typic Haplorthod) and a clay of the Dalhousie association (Typic Haplaquoll)] at Ottawa, Canada. Analysis of field data indicated that leaf stage was highly correlated with growing degree days (base temp of 10°C) accumulated from planting ( r = 0.98). However, air temperature alone did not account for the annual variability in leaf area of mature leaves. To separate leaf expansion from leaf stage, mature area per leaf was plotted as a function of leaf number. The resultant curve had a slightly skewed bell shape whose amplitude represented the leaf area of the largest leaf. When these curves were normalized with respect to their amplitudes they varied little from year to year. The amplitudes compared well ( r =0.87) to plant‐available water averaged from planting to development of the largest leaf and the sum of minimum daily temperature for the same period. Total mature plant leaf area for each year was then calculated by multiplying the integration of the normalized bell shaped curve times the amplitude calculated by the regression equation. These calculated total mature plant leaf areas were used to normalize total plant leaf areas (expanding plus mature leaf area in the absence of senescence). The normalized plant leaf areas were expressed as an S‐shaped logistic function of growing degree days and total plant leaf areas were calculated over each growing season. An additional relationship related water deficit during growth to senescence and the amount of leaf area senesced was subtracted from total plant leaf areas to obtain actual plant leaf area. Estimates of actual plant leaf area for the six growing seasons used to develop the method compared well with measured values ( r between 0.94 and 0.99). Estimates of actual plant leaf area for two independent years at the same location were also good ( r =0.91 and 0.97). This approach reduces prediction of maize leaf area to relatively simple functions of temperature and available water.