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Responses and Ramifications of Rice Canopy Leaf Stratification

Northeast Res. and Ext. Ctr., Univ. of Arkansas, P.O. Box 48, Keiser, AR 72351

^* Corresponding author.

Leaf area within the crop canopy is treated, in various models of canopy processes, as if it were uniform. Crop canopies may, however, be nonuniform in vertical leaf area distribution. Nonuniform vertical leaf area distribution would be expected to affect the responses of rice (Oryza sativa L.) grain yield to leaf area index (LAI). measure of vertical leaf area distribution is proposed: canopy stratification index (CSI) which is the ratio of leaf area in the upper vertical half of the canopy that lower halves. My objectives were to examine (i) the CSI resopnses to rice cultivar, seeding rate, N fertilization rate, and year, and (ii) the relationships of grain yield to LAI for three rice cultivars. A 3.yr field study with three N rates (0, 100, and 200 kg ha^–1), three seeding rates (100, 300, and 500 seeds m^–2), and three cultivars provided the data to examine the questions posed. ‘Lebonnet’ and ‘Le. mont’ rice had higher CSI then did ‘Newbonnet’. There was a parabolic response of grain yield to LAI, with the linear grain yield response phase to LAI being greater for Newbonnet than for Lebonnet, and intermediate between Newbonnet and Lebonnet for Lemont. Optimum LAI was less for Newbonnet than for Lemont and Lebonnet. Therefore, among these cuitivars the grain yield response to LAI was more positive in the linear phase and the optimum LAI for grain yield was lower for the cultivar with the lowest CSI. These data suggest CSI may have value as a selection criterion for yield rice lines by plant breeders.

Received for publication August 9, 1990.