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a Dep. of Agric. and Biosyst. Eng., 124 Davidson Hall, Iowa State Univ., Ames, IA 50011
b Dep. of Agron., Univ. of Nebraska, Lincoln, NE 68588
c Dep. of Agric. and Biosyst. Eng., 219B Davidson Hall, Iowa State Univ., Ames, IA 50011
* Corresponding author (boedhram{at}iastate.edu)
Received for publication April 3, 2000. Amount and vertical distribution of leaf area are essential for estimating radiation interception for canopy photosynthesis modeling. The objective of this study was to quantify vertical distribution of leaf area in corn (Zea mays L.) during the entire growing season. Field experiments were conducted in 1994 and 1995 near Mead, NE. Treatments included irrigation vs. no irrigation and three N rates (0, 68, and 135 kg ha-1). A leaf-dissecting device was built for accurate clipping and collection of leaves at 0.10-m height intervals. A normal curve gave an excellent fit to measured vertical distributions of leaf area index (LAI) at 0.10-m height intervals (r2 > 0.94), regardless of applied N, soil moisture, crop developmental stage, or year. It was concluded that corn LAI was distributed symmetrically in the vertical from crop emergence to maturity. Plots of LAI vertical distributions indicated not only the onset and magnitude of differences among treatments, but also how stress was shared among all canopy layers. Of the three fitted curve parameters, height of symmetry and measure of green-canopy spread were good indicators of plant growth, but LAI in interval containing height of the symmetry axis was not. The existence of a symmetrical vertical distribution of LAI fulfilled the requirement for applying the three-point Gaussian method of integration in corn.
Abbreviations: GS1, Gaussian height above which 11% of total leaf area index is present • GS2, Gaussian height above which 50% of total leaf area index is present • GS3, Gaussian height above which 89% of leaf area index is present • LAI, leaf area index • LAItot, total leaf area index • LAI0.10m, leaf area index per 0.10-m height interval • RMSE, root mean square error • Xopt, midpoint of interval containing Ymax • Ymax, maximum leaf area index per 0.10-m height interval • 
2, measure of green-canopy spread
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